1900 MITSUBISHI DIAMANTE change time

3-60 ENGINE/
-w
remove any covers remaining on the engine such as
on today’s automobiles: the Overhead Valve (OHV)
and the Overhead Camshaft (OHC). The latter can
also be broken down into two subgroups: the Single the rocker arm, front or timing cover and oil pan.
Overhead Camshaft (SOHC) and the Dual Overhead
Camshaft (DOHC). Generally, if there is only a single
camshaft on a head. it is iust referred to as an OHC Some front covers may require the vibration damper
and/or crank pulley to be removed beforehand. The
idea is to reduce the engine to the bare necessities
(cylinder head(s), valve train, engine block, crank-
shaft, pistons and connecting rods), plus any other
‘in block’ components such as oil pumps, balance
shafts and auxiliary shafts.
Finally, remove the cylinder head(s) from the en-
gine block and carefully place on a bench. Disassem-
bly instructions for each component follow later in
this section.
There are two basic types of cylinder heads used
Most cylinder heads these days are made of an
aluminum alloy due to its light weight, durability and
L--L I _--- 1^- _..^ I:,:^^ I I ^...^. .^_ ^^^I :_-_ ..^^ ,L- same environment. The same goes for any other unchanged. One aspect to pay attention to is careful
component on the cylinder head. Think of it as an in- labeling of the parts on the dual camshaft cylinder
“’ surance policy against future problems related to that head. There will be an intake camshaft and followers
component. as well as an exhaust camshaft and followers and
Unfortunately, the only way to find out which com- they must be labeled as such. In some cases, the
ponents need replacing, is to disassemble and care- components are identical and could easily be in-
fully check each piece. After the cylinder head(s) are stalled incorrectly. DO NOT MIX THEM UP! Deter-
disassembled, thoroughly clean all of the compo- mining which is which is very simple; the intake
nents. camshaft and components are on the same side of
DISASSEMBLY the head as was the intake manifold. Conversely, the
exhaust camshaft and components are on the same
side of the head as was the exhaust manifold.
ti See Figures 237 and 238
Whether it is a single or dual overhead camshaft Cup Type Camshaft Followers
cylinder head, the disassembly procedure is relatively 6 See Figures 239, 240, and 241
t “” ““’ 1 Most cylinder heads with cup type camshaft fol-
1 1 head. Also, an engine with an OHV cylinder head is j:, ’
I also known as a pushrod engine. : .; :-,
_I lowers will have the valve spring, retainer and locks
recessed within the followers bore. You will need a
C-clamp style valve spring compressor tool, an OHC
spring removal tool (or equivalent) and a small mag-
net to disassemble the head.
1. If not already removed, remove the camshaft(s)
and/or followers, Mark their positions for assembly.
2. Position the cylinder head to allow use of a C-
clamp style valve spring compressor tool.
IIRN il~llSlt?l ~Lldll~l~S. IlUWttVtJ, MS1 11011 W8S lilt: material of choice in the past, and is still used on
many vehicles today. Whether made from aluminum
or iron, all cylinder heads have valves and seats.
Some use fwo valves per cylinder, while the more hi-
tech engines will utilize a multi-valve configuration
using 3‘4 and even 5 valves per cylinder. When the
valve contacts the seat, it does so on precision ma-
chined surfaces, which seals the combustion cham-
ber, All cylinder heads have a valve guide for each
valve. The auide centers the valve to the seat and al-
lows it to move up and down within it. The clearance
between the valve and guide can be critical. Too
much clearance and the engine may consume oil,
lose vacuum and/or damaae the seat. Too little. and
the valve can stick in the guide causing the engine to
run poorly if at all, and possibly causing severe dam-
age. The last component all cylinder heads have are
valve springs. The spring holds the valve against its
seat. It also returns the valve to this position when
the valve has been opened by the valve train or
camshaft. The spring is fastened to the valve by a re-
tainer and valve locks (sometimes called keepers).
Aluminum heads will also have a valve spring shim
to keep the spring from wearing away the aluminum. Fig, 237 Exploded view of a valve, seal,
1 cylinder head ----r- 1 spring, retamer and locks from an OHC
An ideal method of rebuilding the cylinder head
would involve replacing all of the valves, guides,
seats, springs, etc. with new ones. However, depend-
ing on how the engine was maintained, often this is
not necessary. A major cause of valve, guide and seat
wear is an improperly tuned engine. An engine that is
~~f~t~~ rich, will often wash the lubricating oil
out ofthe guide with gasoline, causing it to wear
~~fdfy. lonely, an engine which is running too
lean wifl pface higher combustion temperatures on
Me valves and seats allowing them to wear or even
bum. Springs fall victim to the driving habits of the
f~~iduaf. A driver who often runs the engine rpm to
tfre redfine will wear out or break the springs faster
then one tfrat stays well below it. Unfortunately,
mileage takes it tot1 on all of the parts. Generally, the
valves, guides, springs and seats in a cylinder head
can be machined and re-used, saving you money.
.However, if a valve is burnt, it may be wise to replace
all of the valves, since they were all operating in the oi a multi-valve cylinder
t has 2 intake
and 2 ex-
At is preferred to position the cylinder head lasket’surtace facing you with tee valve
springs facing the opposite direction and the
lead laying horizontal.
3. With the OHC spring removal adapter tool po-
,itioned inside of the follower bore, compress the
alve spring using the C-clamp style valve spring
:ompressor.
tcca3p51 fig. 239 C-clamp type spring compressor
and an OHC spring removal tool (center) for
cup type followers
Fig. 240 Most cup type follower cylinder
/ heads retain the camshaft using bolt-on
bearing caps

ENGINEANDENGINEOVERHAUL 3-63
Place a straightedge across the gasket surface. Valves
Using feeler gauges, determine the clearance at the
center of the straightedge and across the cylinder Any valves that were not replaced should be
head at several points. Check along the centerline refaced and the tips ground flat. Unless you have ac-
and diagonally on the head surface. If the warpage cess to a valve grinding machine, this should be
exceeds 0.003 in. (0.076mm) within a 6.0 in. done by a machine shop. If the valves are in ex-
(152cm) span, or 0.006 in. (0.152mm) over the total tremely good condition, as well as the valve seats
length of the head, the cylinder head must be resur- and guides, they may be lapped in without petform-
,
I mg macnme worK.
4
It is a recnmmended practice to lap the valves faced. After resurfacing the heads of a V-type engine
the intake manifold flange surface should be checker,
and if necessary, milled proportionally to allow for
the change in its mounting position. _ - _ _ _ .- - - _
even after machine work has been p&formed and/or
new valves have been purchased. This insures a pos-
itive seal between the valve and seat.
-guide clearance; the 1
read
. .
into the cylinder head. Position the dial indicator
against the valve stem near the tie and zero the
gauge. Grasp the valve stem and’wiggle towards and
away from the dial indicator and observe the read-
ings. Mount the dial indicator 90 degrees from the
initial point and zero the gauge and again take a read-
ing. Compare the two readings for a out of round
condition. Check the readings against the specifica-
tions given. An Inside Diameter (I.D.) gauge designed
for valve guides will give you an accurate valve guide
bore measurement. If the I.D. gauge is used, compare
the readings with the specifications given. Any CRACKS AND PHYSICAL DAMAGE
Generally, cracks are limited to the combustion
chamber, hbwever, it is not uncommon for the head
to crack in a spark plug hole, port, outside of the
head or in the valve spring/rocker arm area. The first
area to inspect is always the hottest: the exhaust
.I *
seawpon area.
8 I .,“““I llly”Lv”l~ .ml”“l” - plr”llll”“, ““I ,“a’
because you don’t see a crack does not mean it is not
there. Some more reliable methods for inspecting for
cracks include Magnaflux? a magn$i,c process or
Zyglo? a dye penetrant. Ma{ -’
InatluxW IS used only on
ferrous metal (cast iron) heat Is. Zyglo@ uses a spray
on fluorescent mixture along with a black light to re-
veal the cracks. It is strongly recommended to have
your cylinder head checked professionally for cracks,
especially if the engine was known to have over-
I .* I,. ..^.. LAPPING THE VALVES
*Before iaoaino the valves to the seats,
read the rest of the cylinder head section to
insure that any related parts are in accept-
able enough condition to continue.
*Before anv valve seat machining and/or
lapping can be performed, the guides must
be within factory recommended specifica-
tions.
1. Invert the cylinder head.
2. Linhtlv Iuhrir;rB the valve stems and insert
-. _ ~ . . . . . .--.._-._
them into the cylinder head in their numbered order.
3. Raise the valve from the seat and apply a small
amount of fine lanninn compound to the seat.
4.
i guides that fail these inspections should be replaced nearea analor ieaKea or consumea coolant. Contact a Moisten the suction head of a hand-lapping
tool and attach it to the head of the valve.
i or machined. local shop for availability and pricing of these ser-
5. Rotate the tool between the palms of both
I vices.
I
VALVE SEATS Physical damage is usually very evident. For ex- hands, changing the position of the valve on the
valve seat and lifting the tool often to prevent groov-
A visual inspection of the valve seats should show
amnb P hrnbn mntlntinn ear from dropping the I and/or bolt. All of these ing.
.a,... . 6. Lap the valve until a smooth, polished circle is
a slightly worn and pitted surface where the valve
face contacts the seat. Inspect the seat carefully for
severe pitting or cracks. Also, a seat that is badly
worn will be recessed into the cylinder head. A se-
verely worn or recessed seat may need to be re- uetecIs SIIOUIO oe nxea or, IT unrepairaole, me neaa
should be replaced.
Camshaft and Followers evid
7
traces of the grinding corn
to maintain its lapped loca lent on the valve and seat.
‘. Remove the tool and the valve. Wipe away all
pound and store the valve
placed: All cracked seats must be replaced. A seat
concentricity gauge, if available, should be used to
check the seat run-out. If run-out exceeds specifica-
tions the seat must be machined (if no soecification
is given use 0.002 in. or O.O51mt$. Inspect the camshaft(s) and followers as described
earlier in this section.
REFINISHING & REPAIRING Do not get the valves out of order after they
have been lapped. They must be put back
: ..^^ I... --I:^:-L!-- --A
Many of the procedures gIveI
WI WIIIIISIIIIIIJ ~IIU repairing the cylinder head components must be per-
formed by a machine shop. Certain steps, if the in-
spected part is not worn, can be performed yourself
inexpensively. However, you spent a lot of time and
effort so far, why risk trying to save a couple bucks if
you might have to do it all over again?
I- with the same valve seat with which they
were lapped.
Springs, Retainers and Valve locks
There is no repair or refinishing possible with the
springs, retainers and valve locks. If they are found to
be worn or defective, they must be replaced with new
lor known nnod narts CYLtNDEt? HEAD SURFACE FLATNESS
) See Figures 256 and 257
After you have cleaned the gasket surface of the
cylinder head of any old gasket material, check the
head for flatness.
\- - a---r r- .-.
Cylinder Head
Most refinishing procedures dealing with the
VALVE GWDE
elf any machining or replacements are
e valve guides, the seats must be
Fig. 257 Checks should also be made along Unless the valve guides need machining or re-
placing, the only service to perform is to thoroughly‘
clean them of any dirt or oil residue.

4-2 DRIVEABILITYAND EMISSIONS CONTROLS
OPERATION
p See Figures 1, 2, and 3
All engines are equipped with the Positive
Crankcase Venhlation (PCV) system. The PCV sys-
tem vents crankcase gases into the engine air intake
where they are burned with the fuel and air mrxture.
The PCV system keeps pollutants from being re-
leased into the atmosphere It also helps to keep the
engine 011 clean, by ridding the crankcase of moisture
and corrosive fumes. The PCV system consists of the
PCV valve, the nipple in the air intake and the con-
necting hoses.
Incorrect operation of the PCV system can cause
multiple driveability symptoms.
A plugged valve or hose may cause’
l Rough Idle l Stalling or slow idle speed l Oil leaks
tT9574goi Fig. 1 Typical PCV system airflow
89574g0r5 Fig. 3 . . .
or mounted in a grommet on the
valve cover
l Sludge in en ine
A leakrng valve or ose would cause: i?
l Rough idle l Stalling l High idle speed
p See Figures 4 and 5
1. Disconnect the ventilation hose from the PCV
valve. Remove the PCV valve from the engine Once
removed, reconnect the ventilation hose to the valve.
2. Start the engine and allow to idle. Place a fin-
ger over open end of the PCV valve. Make sure intake
manifold vacuum is felt on finger.
3. If vacuum is not felt, the PCV valve may be re-
stricted.
4. Turn the engine
OFF and remove the PCV
valve from the hose.
5. Insert a thin stick into the threaded end of the
PCV valve. Push on the inner plunger and inspect for
movement.
6. If plunger inside the PCV valve is not free to
move back and forth, the valve is clogged and WIII re-
quire replacement.
*It is possible to clean the valve using the
appropriate solvent, but replacement is rec-
ommended.
REMOVAL&INSTALLATION
For PCV valve removal and installation, please re-
fer to Section 1 of this manual.
89574QO’ Fig. 4 With the engine idling, check the end
of the PCV valve to see if vacuum is present
Positive crankcase
ventilation
89574go6 Fig. 5 Inspect the PCV valve for inner
plunger movement. If the plunger is bound
or sticking, replace the valve OPERATION
p See Figures 6 and 7
Changes in atmospheric temperature cause fuel
tanks to breathe, that is, the air within the tank ex-
pands and contracts with outside temperature
changes. If an unsealed system was used, when the
temperature rises, air would escape through the tank
vent tube or the vent in the tank cap. The air which
escapes contains gasoline vapors.
The Evaporative Emission Control System pro-
vides a sealed fuel system with the capability to store
and condense fuel vapors. When the fuel evaporates
in the fuel tank, the vapor passes through the EVAP
emission valve, through vent hoses or tubes to a car-
bon filled evaporative canister. When the engine is
operahng the vapors are drawn into the intake mani-
fold and burned during combustion.
A sealed, maintenance free evaporative canister is
used The canister is filled wrth granules of an acti-
vated carbon mixture. Fuel vapors entering the canis-
ter are absorbed by the charcoal granules. A vent cap
is located on the top of the canister to provide fresh
air to the canister when it is being purged. The vent
cap opens to provide fresh air into the canister, which
circulates through the charcoal, releasing trapped va-
pors and carrying them to the engine to be burned.
Fuel tank pressure vents fuel vapors into the can-
ister. They are held in the canister until they can be
drawn into the intake manifold. The canister purge
valve allows the canister to be purged at a pre-deter-
mined time and engine operating conditions.
Vacuum to the canister is controlled by the canis-
ter purge valve. The valve IS operated by the PCM.
The PCM regulates the valve by switching the ground
circuit on and off based on engine operating condi-
tions When energized, the valve prevents vacuum
from reaching the canister. When not energized the
valve allows vacuum to purge the vapors from the
canister.
During warm up and for a specified time after hot
starts, the PCM energizes (grounds) the valve pre-
venting vacuum from reaching the canrster. When the
engine temperature reaches the operating level of
about 120°F (49°C) the PCM removes the ground
from the valve allowing vacuum to flow through the
canister and purges vapors through the throttle body.
During certain Idle conditions, the purge valve may
be grounded to control fuel mixture calibrations.
The fuel tank is sealed with a pressure-vacuum re-
lief filler cap. The relief valve in the cap is a safety
feature, preventing excessive pressure or vacuum in
the fuel tank. If the cap is malfunctioning, and needs
to be replaced, ensure that the replacement is the
identical cap to ensure correct system operation,
OBD-II EVAP System Monitor
Some models have added system components
due to the EVAP system monitor incorporated in the
OBD-II engrne control system. A pressure sensor is
mounted on the fuel tank which measures pressure
inside the tank, and a purge flow sensor measures
the flow of the gases from the canister into the en-
gine.
The PCM can store trouble codes for EVAP sys-
tem performance, a list of the codes is provided later

DRIVEABILITYAND EMISSIONS CONTROLi 4-11
fold. Resistance changes in response to the ambient
air temperature. The sensor has a negative tempera-
ture coefficient. As the temperature of the sensor
rises the resistance across the sensor decreases. Thil
provides a signal to the PCM indicating the tempera-
ture of the incoming air charge. This sensor helps the
PCM to determine spark timing and air/fuel ratio. In-
formation from this sensor is added to the pressure
sensor information to calculate the air mass being
sent to the cylinders. The IAT receives a 5-volt refer-
ence signal and the signal return is based upon the
change in the measured resistance due to tempera-
ture.
TESTING
b See Figures 54, 55, 56, 57, and 58
Fig. 54 Testing the resistance of the IAT
sensor across the two sensor pins
Fig. 55 The IAT sensor can be monitored
with an appropriate and Data-stream capa-
ble scan tool
~1 b. Sensor temperature of 68°F (2O”C)--‘ 2.>3.0 kilo-ohms c. Sensor temperature of 176°F (SO*C)-
0.30-0.42 kilo-ohms
5. Measure the sensor resistance while heating
the sensor area with a hair dryer. As the temperature
of the sensor increases, sensor resistance should be-
come smaller.
6. If the measured resistance deviates from the
standard value or the resistance remains unchanged,
replace the air flow sensor assembly.
1 REMOVAL&INSTALLATION
The IAT sensor is part of the Mass Air Flow (MAF)
sensor. The IAT sensor cannot be replaced sepa-
rately. Refer to MAF sensor removal and installation
in this section.
- OPERATION a9574g72 Fig. 56 IAT sensor terminal identification;-
1990-93 Galant The Mass Air Flow (MAF) sensor directly mea-
lres the mass of air being drawn into the engine.
I ?he sensor output is used to calculate injector pulse
width. The MAF sensor is what is referred to as a
“hot-wire sensor”. The sensor uses a thin platinum
wire filament, wound on a ceramic bobbin and coated
with glass, that is heated to 417°F (200°C) above the
amh+en+ nir +PmnPrfijre and subiected to the intake
..I._ ~ ..-.. .“..‘r-,u.. ai mow stream. A “cold-wire” is used inside the MAF
sensor resuirance wnoe nearmg ir wnn a 1
hair drier ‘hat melt: IS al I~“< ,“.., lvllQ UtiLnbtill ,,,=
tnd GND terminals of the MAF sensor connec-
tor. If voltaae is not within specification, check power
1. Detach the air flow sensor electrical connector.
2. Measure the resistance between terminals No.
4 and No. 6 of the electrical connector, except on the
2.OL DOHC turbo engine.
3. ff equipped with the 2.OL DOHC turbo engine,
measure the resistance between terminals No. 6 and
No. 8 of the sensor electric connector.
4. Compare test readings to the following specifi-
cations:
a. Sensor temperature of 32°F (O“C)--
5.3-6.7 kilo-ohms and groundcircuits and repair as necessary.
verify that there is at least 4.5 volts between the SIG 3. With the ignition key ON, and,the engine ON,
and GND terminals of the MAF sensor connector. If
voltage is not within specification, check power and
ground circuits and repair as necessary.
4. With the ignition key ON, and the engine ON,
check voltage between GND and SIG RTN terminals.
Voltage should be approximately 0.34-l .96 volts. If
voltage is not within specification, the sensor may be
faulty.
/ sensor to determine the ambient air temperature.
Battery voltage, a reference signal, and a ground
signal from the PCM are supplied to the MAF sensor.
rho ~pn**r rp+++rns a signal proportionate to the cur-
re. The increased airflow across the
s a cooling fan, lowering the resis-
mo more current to maintain the tem- tance and requir
e^-‘.._^ ^I LL^
I
Intake air temper- pe~a+ure UI me wire. The increased current is mea- aturf sensor sured by the voltage in the circuit, as current
increases, voltage increases. As the airflow increases
the signal return voltage of a normally operating MAF
sensor will increase.
, ~~1 TESTING - II ire” at the re-
89574g74 Fig. 58 Measure the intake air temperature
-----_ ---1-a---- L..- L--1. . . .*a 1. Using a multimeter, check for voltage by back-
nrr\hinn +hn MAF sensor connector.
the ignition key ON, and the engine OFF, .^-^ :- -’ ‘.txt In E; \mltr hahrman tha veriry t
BAT-T i

5-8 FUELSYSTEM
9 ,npimr w1m.m
1: i”“L,
1: 82”w
93155gx Fig. 31 Exploded view of the fuel injectors and related components-
s.OL engines
Observe all applicable safety precautions
when working around fuel. Whenever servic-
ing the fuel system, always work in a well
ventilated area. Do not allow fuel spray or
vapors to come in contact with a spark or
open flame. Keep a dry chemical fire extin-
guisher near the work area. Always keep fuel
in a container specifically designed for fuel
storage; also, always properly seal fuel con-
tainers to avoid the possibility of fire or ex-
plosion.
6. Disconnect the fuel return hose and remove
the O-ring.
7. Disconnect the vacuum hose from the fuel
pressure regulator.
8. Detach the electrical connectors from each
injector.
9. Remove the fuel pipe connectmg the fuel
rails. Remove the injector rail retaining bolts. Make
sure the rubber mounting bushings do not get lost.
10. Lift the rail assemblies up and away from the
engine.
11. Remove the injectors from the rail by pulling
gently. Discard the lower insulator.
To install:
*Some of the vehicles may have a clip that
secures the injector to the fuel rail. Be sure
to remove or install the injector clip where
necessary.
12. Install a new grommet and O-ring to the in-
jector. Coat the O-ring with light oil.
13. Install the injector to the fuel rail.
14. Replace the seats in the intake manifold. In-
stall the fuel rails and injectors to the manifold. Make
sure the rubber bushings are in place before tighten-
ing the mounting bolts.
15. Tighten the retaining bolts to 7-9 ft. Ibs.
(W-13 Nm) Install the fuel pipe with new gasket.
16. Attach the electrical connectors to the injec-
tors
Fig. 32 Exploded view of the fuel injectors and related components-
3.5L engine
17. Connect the fuel return hose.
18. Replace the O-ring, lightly lubricate it and
connect the high pressure fuel line.
19. Usmg new gaskets, install the intake plenum
and all related items. Refer to Section 3.
20. Fill the cooling system.
21. Connect the negative battery cable and check
the entire system for proper operation and leaks.
The easiest way to test the operation of the fuel in-
jectors is to listen for a clicking sound coming from
the injectors while the engine IS running. This is ac-
complished using a mechanic’s stethoscope, or a
long screwdriver. Place the end of the stethoscope or
the screwdriver (tip end, not handle) onto the body of
the injector. Place the ear pieces of the stethoscope
in your ears, or if using a screwdriver, place your ear
on top of the handle. An audible chcking noise
should be heard; this is the solenoid operating. If the
injector makes this noise, the injector driver circuit
and computer are operating as designed. Continue
testing all the injectors this way.
Be extremely careful while working on an op-
erating engine, make sure you have no dan-
gling jewelry, extremely loose clothes,
power tool cords or other items that might
get caught in a moving part of the ermine.
All Injectors Clicking
If all the injectors are clicking, but you have de-
termined that the fuel system is the cause of your
driveability problem, continue diagnostics. Make
sure that you have checked fuel pump pressure as
outlined earlier in this section. An easy way to de-
termine a weak or unproductive cylinder is a cylin-
der drop test. This is accomplished by removing
one spark plug wire at a time, and seeing which cylinder causes the least difference in the idle.
The one that causes the least change is the weak
cylinder.
If the injectors were all clicking and the ignition
system is functioning properly, remove the injector of
the suspect cylinder and bench test it. This is accom-
plished by checking for a spray pattern from the in-
jector itself Install a fuel supply line to the injector
(or rail if the injector is left attached to the rail) and
momentarily apply 12 volts DC and a ground to the
injector itself; a visible fuel spray should appear. If no
spray is achieved, replace the injector and check the
running condition of the engine.
One or More Injectors Are Not Clicking
6 See Figures 33, 34, 35, and 36
If one or more injectors are found to be not operat-
ing, testing the injector driver circuit and computer
can be accomplished using a “noid” light. First, with
the engine not running and the ignition key in the
OFF position, remove the connector from the injector
you plan to test, then plug the “noid” light tool into
the injector connector. Start the engine and the
“noid” light should flash, signaling that the injector
driver circuit is working. If the “noid” light flashes,
but the injector does not click when plugged in, test
the injectors resistance. Resistance should be be-
tween:
l All non-turbo engines: 13-16 ohms at 68°F
(20°C)
l Turbocharged engines: 2-3 ohms at 68 “F
(20°C)
If the “noid” light does not flash, the injector dri-
ver circuit is faulty. Disconnect the negative battery
cable. Unplug the “noid” light from the injector con-
nector and also unplug the PCM. Check the harness
between the appropriate pins on the harness side of
the PCM connector and the injector connector. Re-
sistance should be less than 5.0 ohms; if not, repair
the circuit. If resistance
IS within specifications, the
injector driver inside the PCM is faulty and replace-
ment of the PCM will be necessary.

.
5-16 FUELSYSTEM
6. Disconnect the return hose and the high
pressure fuel hose.
7. Using special tool MB991480 or equivalent,
remove the fuel pump retaining cap and remove the
pump assembly.
Observe all applicable safety precautions
when working around fuel. Whenever servic-
ing the fuel system, always work in a well
ventilated area. Do not allow fuel spray or
vapors to come in contact with a spark or
open flame. Keep a dry chemical fire extin-
guisher near the work area. Always keep fuel
in a container specifically designed for fuel
storage; also, always properly seal fuel con-
tainers to avoid the possibility of fire or ex-
plosion.
To install:
*If the packing material is damaged or de-
formed, replace it with new packing.
8. Install the packing to the fuel tank.
9. Install the fuel pump assembly to the tank
and align the mating marks on the pump and the
floorpan.
10. Tighten the fuel pump retaining cap using
tool MB991480 or equrvalent.
11. Connect the high pressure hose, return hose
and the fuel tank wirmg.
12. Connect the negative battery cable.
13. Check the fuel pump for proper pressure and
inspect the entire system for leaks.
14. Apply sealant to the access cover and install
the cover.
15. Install the rear seat cushion.
TESTING
1. Relieve fuel system pressure.
2. Disconnect the battery negative cable.
3. Disconnect the fuel hrgh pressure hose at the
delivery pipe side.
Observe all applicable safety precautions
when working around fuel. Whenever servic-
ing the fuel system, always work in a well
ventilated area. Do not allow fuel spray or
vapors to come in contact with a spark or
open flame. Keep a dry chemical fire extin-
guisher near the work area. Always keep fuel
in a container specifically designed for fuel
storage; also, always properly seal fuel con-
tainers to avoid the possibility of fire or ex-
alosion.
4. Connect a fuel pressure gauge to tools
MD998709 and MD998742 or exact equivalent, with
appropriate adapters, seals and/or gaskets to prevent
leaks during the test. Install the gauge and adapter
between the delivery pipe and high pressure hose. In-
stall carefully to prevent leaks.
5. Connect the negative battery cable.
6. Apply battery voltage to the terminal for fuel
pump activation (located in the engine compartment)
to run the fuel pump, and check for leaks.
7. Start the engine and run at curb idle speed.
8. Measure the fuel pressure and compare to
the specifications listed in the chart in Section 1.
9. Locate and disconnect the vacuum hose run-
ning to the fuel pressure regulator. Plug the end of
the hose and record the fuel pressure again. The fuel
pressure should have increased approximately IO
psi. 10. Reconnect the vacuum hose the fuel pressure
regulator. After the fuel pressure stabilizes, race the
engine 2-3 times and check that the fuel pressure
does not fall when the engine is running at idle.
il. Check to be sure there is fuel pressure in the
return hose by gently pressing the fuel return hose
with fingers while racing the engine. There will be no
fuel pressure in the return hose when the volume of
fuel flow is low.
12. If fuel pressure is too low, check for a
clogged fuel filter, a defective fuel pressure regulator
or a defective fuel pump, any of which will require re-
placement.
13. If fuel pressure is too high, the fuel pressure
regulator is defective and will have to be replaced or
the fuel return is bent or clogged. If the fuel pressure
readmg does not change when the vacuum hose is
disconnected, the hose is clogged or the valve is
stuck in the fuel pressure regulator and it will have to
be replaced.
14. Stop the engine and check for changes in the
fuel pressure gauge. It should not drop. If the gauge
reading does drop, watch the rate of drop. If fuel
pressure drops slowly, the likely cause is a leaking
injector which will require replacement. If the fuel
pressure drops immediately after the engine is
stopped, the check valve in the fuel pump isn’t clos-
ing and the fuel pump will have to be replaced.
15. Relieve fuel system pressure.
16. Disconnect the high pressure hose and re-
move the fuel pressure gauge from the delivery pipe.
17. Install a new O-ring in the groove of the high
pressure hose. Connect the hose to the delivery pipe
and tighten the screws. After Installation, apply bat-
tery voltage to the terminal for fuel pump activation to
run the fuel pump. Check for leaks.

6-2 CHASSIS ELECTRICAL
) See Figure 1
For any 12 volt, negative ground, electrical system
to operate, the electricity must travel in a complete
circurt. This simply means that current (power) from
the posibve (t) terminal of the battery must eventu-
ally return to the negative (-) terminal of the battery.
Along the way, this current will travel through wires,
fuses, switches and components. If, for any reason,
the flow of current through the circuit is interrupted,
the component fed by that circuit will cease to func-
tion properly.
Perhaps the easiest way to visualize a circuit is to
think of connecting a light bulb (with two wires at-
tached to it) to the battery-one wire attached to the
negative (-) terminal of the battery and the other wire
to the positive (t) terminal. With the two wires touch-
ing the battery terminals, the circuit would be com-
plete and the light bulb would illummate. Electricity
would follow a path from the battery to the bulb and
back to the battery. It’s easy to see that wrth longer
wires on our light bulb, it could be mounted any-
where. Further, one wire could be fitted with a switch
so that the light could be turned on and off.
The normal automotive circuit differs from this
simple example in two ways, Frrst, instead of having
a return wire from the bulb to the battery, the current
travels through the frame of the vehicle. Since the
negative (-) battery cable is attached to the frame
(made of electrically conductive metal), the frame of
the vehicle can serve as a ground wire to complete
the circuit. Secondly, most automotive circuits con-
tain multiple components which receive power from a
single circuit. This lessens the amount of wire
needed to power components on the vehicle.
HOW DOES ELECTRlClTYWORK:THE
WATER ANALOGY
Electricity is the flow of electrons-the subatomic
particles that constitute the outer shell of an atom.
Electrons spin in an orbit around the center core of
RETURN
RETURN
CONDUCTOR
CONDUCTOR
GROUND
GROUND
lccs2w
Fig. 1 This example illustrates a simple cir-
cuit. When the switch is closed, power from
the positive (t) battery terminal flows
through the fuse and the switch, and then
to the light bulb. The light illuminates and
the circuit is completed through the ground
wire back to the negative (-) battery termi-
nal. In reality, the two ground points shown
in the illustration are attached to the metal
frame of the vehicle, which completes the
circuit back to the battery
an atom The center core is comprised of protons
(positive charge) and neutrons (neutral charge). Elec-
trons have a negative charge and balance
out the
positive charge of the protons. When an outside force
causes the number of electrons to unbalance the
charge of the protons, the electrons will split off the
atom and look for another atom to balance out. If this
imbalance is kept up, electrons will continue to move
and an electrical flow will exist.
Many people have been taught electrical theory
using an analogy with water. In a comparison wrth
water flowing through a pipe, the electrons would be
the water and the wire is the pipe.
The flow of electricity can be measured much like
the flow of water through a pipe. The unit of measure-
ment used is amperes, frequently abbreviated as
amps (a). You can compare amperage to the volume
of water flowing through a pipe. When connected to a
circuit, an ammeter WIII measure the actual amount of
current flowing through the circuit. When relatively
few electrons flow through a circuit, the amperage is
low. When many electrons flow, the amperage is
high.
Water pressure is measured in units such as
pounds per square inch (psi); The electrical pressure
is measured in unrts called volts (v). When a volt-
meter is connected to a circuit, it is measuring the
electrical pressure.
The actual flow of electricity depends not only on
voltage and amperage, but also on the resistance of
the circuit The higher the resistance, the higher the
force necessary to push the current through the cir-
cuit. The standard unit for measuring resistance is an
ohm. Resistance in a crrcuit varies dependmg on the
amount and type of components used in the circuit.
The main factors which determine resistance are:
l Material-some materials have more resis-
tance than others Those with high resistance are said
to be insulators Rubber materials (or rubber-like
plashcs) are some of the most common insulators
used in vehicles as they have a very high resistance
to electricity Very low resistance materials are said to
be conductors. Copper wire is among the best con-
ductors. Silver is actually a superior conductor to
copper and is used in some relay contacts, but its
high cost prohibits its use as common wiring Most
automotive wiring is made of copper.
l Size-the larger the wire size being used, the
less resistance the wire will have. This IS why com-
ponents which use large amounts of electricity usu-
ally have large wires supplying current to them.
l Length-for a given thickness of wire, the
longer the wire, the greater the resistance. The
shorter the wire, the less the resistance. When deter-
mining the proper wire for a circuit, both size and
length must be considered to design a circuit that can
handle the current needs of the component.
l Temperature-with many materials, the higher
the temperature, the greater the resistance (positive
temperature coefficient). Some materials exhibit the
opposite trait of lower resistance with higher temper-
atures (negative temperature coefficient). These prin-
ciples are used in many of the sensors on the engine
OHM'S LAW
There is a direct relationship between current,
voltage and resistance. The relationship between cur- rent, voltage and resistance can be summed up by a
statement known as Ohm’s law.
Voltage (E) is equal to amperage (I) times resis-
tance (R): E=l x R
Other forms of the formula are R=E/I and I=E/R
In each of these formulas, E is the voltage in volts,
I is the current in amps and R IS the resistance in
ohms. The basic point to remember is that as the re-
sistance of a circuit goes up, the amount of current
that flows in the circuit will go down, if voltage re-
mains the same.
The amount of work that the electricity can perform
is expressed as power. The unit of power is the watt
(w). The relationship between power, voltage and
current
IS expressed as:
Power(w) is equal to amperage (I) times voltage
(E): W=l x E
This is only true for direct current (DC) circuits:
The alternating current formula is a tad different, but
since the electrical circuits in most vehicles are DC
type, we need not get into AC circuit theory.
POWERSOURCE
Power is supplied to the vehicle by two devices:
The battery and the alternator. The battery supplies
electrical power during starting or during periods
when the current demand of the vehicle’s electrical
system exceeds the output capacity of the alternator.
The alternator supplies electrical current when the
engine is running
Just not does the alternator supply
the current needs of the vehicle, but it recharges the
battery.
The Battery
In most modern vehicles, the battery is a lead/acid
electrochemical device consisting of six 2 volt sub-
sections (cells) connected in series, so that the unit
is capable of producing approximately 12 volts of
electrical pressure. Each subsection consists of a se-
ries of positive and negative plates held a short dis-
tance apart in a solutron of sulfuric acid and water.
The two types of plates are of dissimilar metals,
This sets up a chemrcal reaction, and it is this reac-
tion which produces current flow from the battery
when Its positive and negattve terminals are con-
nected to an electrical load. The power removed from
the battery is replaced by the alternator, restoring the
battery to its original chemical state.
The Alternator
On some vehicles there isn’t an alternator, but a
generator. The difference IS that an alternator sup-
plies alternating current which is then changed to di-
rect current for
use on the vehicle, while a generator
produces direct current. Alternators tend to be more
efficient and that is why they are used.
Alternators and generators are devices that consist
of coils of wires wound together making big electro-
magnets. One group of coils spins within another set
and the interaction of the magnetic fields causes a
current to flow. This current is then drawn off the
coils and fed into the vehicles electrical system.

I
6-4 CHASSIS ELECTRICAL
I
printed circuit is sandwiched between two sheets of
plastic for more protection and flexibility. A complete l Weatherproof-these connectors are most the jumper wire is of too small a gauge, it
printed circuit, consisting of conductors, insulating commonly used where the connector is exposed to
may overheat and possibly melt. Never use
material and connectors for lamps or other compo- the elements. Terminals are protected against mois-
nents is called a printed circuit board. Printed cir- ture and dirt by sealing rings which provide a weath- jumpers to bypass high resistance loads in a
et-tight seal. All repairs require the use of a special circuit. Bypassing resistances, in effect, cre-
cuitry is used in place of individual wires or har- ates a short circuit. This may, in turn, cause
nesses in places where space is limited, such as terminal and the tool required to service it. Unlike
behind instrument panels. standard blade type terminals, these weatherproof damage and fire. Jumper wires should only
be used to bypass lengths of wire or to simu-
Since automotive electrical systems are very sen- terminals cannot be straightened once they are bent. late switches.
sitive to changes in resistance, the selection of prop- ‘Make certain that the connectors are properly seated
erly sized wires is critical when systems are repaired, and all of the sealing rings are in place when con-
netting leads. Jumper wires are simple, yet extremely valuable,
A loose or corroded connection or a replacement wire pieces of test equipment. They are basically test wires
that is too small for the circuit will add extra resis-
l Molded-these connectors require complete which are used to bypass sections of a circuit. Al-
replacement of the connector if found to be defective.
tance and an additional voltage drop to the circuit. though jumper wires can be purchased, they are usu-
The wire gauge number is an expression of the This means splicing a new connector assembly into ally fabricated from lengths of standard automotive
cross-section area of the conductor. Vehicles from the harness. All splices should be soldered to insure
proper contact. Use care when probing the connec- wire and whatever type of connector (alligator clip,
countries that use the metric system will typically de- spade connector or pin connector) that is required for
scribe the wire size as its cross-sectional area in tions or replacing terminals in them, as it is possible
square millimeters. In this method, the larger the to create a short circuit between opposite terminals. If the particular application being tested. In cramped,
hard-to-reach areas, it is advisable to have insulated
wire, the greater the number. Another common sys- this happens to the wrong terminal pair, it is possible
to damage certain components. Always use jumper boots over the jumper wire terminals in order to pre-
tern for expressing wire size is the American Wire vent accidental grounding. It is also advisable to in-
Gauge (AWG) system. As gauge number increases, wires between connectors for circuit checking and
NEVER probe through weatherproof seals. elude a standard automotive fuse in any jumper wire.
area decreases and the wire becomes smaller. An 18
gauge wire is smaller than a 4 gauge wire. A wire
l Hard Shell-unlike molded connectors, the This is commonly referred to as a “fused jumper”. By
inserting an in-line fuse holder between a set of test
terminal contacts in hard-shell connectors can be re-
with a higher gauge number will carry less current
placed. Replacement usually involves the use of a leads, a fused jumper wire can be used for bypassing :
than a wire with a lower gauge number. Gauge wire open circuits. Use a 5 amp fuse to provide protection
size refers to the size of the strands of the conductor, special terminal removal tool that depresses the lock- against voltage spikes.
not the size of the complete wire with insulator. It is ing tangs (barbs) on the connector terminal and al-
lows the connector to be removed from the rear of the Jumper wires are used primarily to locate open
possible, therefore, to have two wires of the same
shell. The connector shell should be replaced if it electrical circuits, on either the ground (-) side of the
gauge with different diameters because one may have
thicker insulation than the other. shows any evidence of burning, melting, cracks, or circuit or on the power (+) side. If an electrical corn-
breaks. Replace individual terminals that are burnt, ponent fails to operate, connect the jumper wire be-
It is essential to understand how a circuit works
corroded, distorted or loose. tween the component and a good ground. If the corn-
before trying to figure out why it doesn’t. An electrical ponent operates only with the jumper installed, the
schematic shows the electrical current paths when a ground circuit is open. If the ground circuit is good,
circuit is operating properly. Schematics break the but the component does not operate, the circuit be-
entire electrical system down into individual circuits. tween the power feed and component may be open. ’
In a schematic, usually no attempt is made to repre- Pinpointing the exact cause of trouble in an elec- By moving the jumper wire successively back from
trical circuit is most times accomplished by the use the component toward the power source, you can
; : sent wiring and components as they physically ap-
pear on the vehicle; switches and other components of special test equipment. The following describes isolate the area of the circuit where the open is lo-
are shown as simply as possible. Face views of har- different types of commonly used test equipment and cated. When the component stops functioning, or the f
j
ness connectors show the cavity or terminal locations briefly explains how to use them in diagnosis. In ad- power is cut off, the open is in the segment of wire j
in all multi-pin connectors to help locate test points. dition to the information covered below, the tool between the jumper and the point previously tested.
! manufacturer’s instructions booklet (provided with You can sometimes connect the jumper wire di-
the tester) should be read and clearly under.$ood be- rectly from the battery to the “hot” terminal of the I
CONNECTORS 1 fore attempting any test procedures. component, but first make sure the component uses 1
# See Figures 5 and 6 JUMPER WIRES 12 volts in operation. Some electrical components, i
such as fuel injectors or sensors, are designed to op-
Three types of connectors are commonly used in erate on about 4 to 5 volts, and running 12 volts di- j
)
automotive applications-weatherproof, molded and rectly to these components will cause damage.
hard shell.
Never use jumper wires made from a thinner TEST LIGHTS I
gauge wire than the circuit being tested. If
# See Figure 7
The test light is used to check circuits and compo-
I nents while electrical current is flowing through
Fig. 5 Hard shell (left) and weatherproof
(right) connectors have replaceable termi- Fig. 7 A 12 volt test light is used to di%
nals
ements 1 the presence of voltage in a circuit