full load. The Kent-Moore J-39021 is such a tool, though there are
others. The Kent-Moore costs around $240 at the time of this writing
and works on many different manufacturer's systems.
The second method is to use a lab scope. Remember, a lab
scope allows you to see the regular operation of a circuit in real
time. If an injector is having an short or intermittent short, the lab
scope will show it.
Checking Available Voltage At the Injector
Verifying a fuel injector has the proper voltage to operate
correctly is good diagnostic technique. Finding an open circuit on the
feed circuit like a broken wire or connector is an accurate check with
a DVOM. Unfortunately, finding an intermittent or excessive resistance
problem with a DVOM is unreliable.
Let's explore this drawback. Remember that a voltage drop due
to excessive resistance will only occur when a circuit is operating?
Since the injector circuit is only operating for a few milliseconds at
a time, a DVOM will only see a potential fault for a few milliseconds.
The remaining 90+% of the time the unloaded injector circuit will show
normal battery voltage.
Since DVOMs update their display roughly two to five times a
second, all measurements in between are averaged. Because a potential
voltage drop is visible for such a small amount of time, it gets
"averaged out", causing you to miss it.
Only a DVOM that has a "min-max" function that checks EVERY
MILLISECOND will catch this fault consistently (if used in that mode).\
The Fluke 87 among others has this capability.
A "min-max" DVOM with a lower frequency of checking (100
millisecond) can miss the fault because it will probably check when
the injector is not on. This is especially true with current
controlled driver circuits. The Fluke 88, among others fall into this
category.
Outside of using a Fluke 87 (or equivalent) in the 1 mS "min-\
max" mode, the only way to catch a voltage drop fault is with a lab
scope. You will be able to see a voltage drop as it happens.
One final note. It is important to be aware that an injector
circuit with a solenoid resistor will always show a voltage drop when
the circuit is energized. This is somewhat obvious and normal; it is a
designed-in voltage drop. What can be unexpected is what we already
covered--a voltage drop disappears when the circuit is unloaded. The
unloaded injector circuit will show normal battery voltage at the
injector. Remember this and do not get confused.
Checking Injector On-Time With Built-In Function
Several DVOMs have a feature that allows them to measure
injector on-time (mS pulse width). While they are accurate and fast to\
hookup, they have three limitations you should be aware of:
* They only work on voltage controlled injector drivers (e.g
"Saturated Switch"), NOT on current controlled injector
drivers (e.g. "Peak & Hold").
* A few unusual conditions can cause inaccurate readings.
* Varying engine speeds can result in inaccurate readings.
Regarding the first limitation, DVOMs need a well-defined
injector pulse in order to determine when the injector turns ON and
OFF. Voltage controlled drivers provide this because of their simple
switch-like operation. They completely close the circuit for the
entire duration of the pulse. This is easy for the DVOM to interpret.
The other type of driver, the current controlled type, start
off well by completely closing the circuit (until the injector pintle
opens), but then they throttle back the voltage/current for the
duration of the pulse. The DVOM understands the beginning of the pulse
CURRENT WAVEFORM SAMPLES
EXAMPLE #1 - VOLTAGE CONTROLLED DRIVER
The waveform pattern shown in Fig. 4 indicate a normal
current waveform from a Ford 3.0L V6 VIN [U] engine. This voltage
controlled type circuit pulses the injectors in groups of three
injectors. Injectors No. 1, 3, and 5 are pulsed together and cylinders
2, 4, and 6 are pulsed together. The specification for an acceptable
bank resistance is 4.4 ohms. Using Ohm's Law and assuming a hot run
voltage of 14 volts, we determine that the bank would draw a current
of 3.2 amps.
However this is not the case because as the injector windings
become saturated, counter voltage is created which impedes the current
flow. This, coupled with the inherent resistance of the driver's
transistor, impedes the current flow even more. So, what is a known
good value for a dynamic current draw on a voltage controlled bank of
injectors? The waveform pattern shown below indicates a good parallel
injector current flow of 2 amps. See Fig. 4.
Note that if just one injector has a resistance problem and
partially shorts, the entire parallel bank that it belongs to will
draw more current. This can damage the injector driver.
The waveform pattern in Fig. 5 indicates this type of problem
with too much current flow. This is on other bank of injectors of the
same vehicle; the even side. Notice the Lab Scope is set on a one amp
per division scale. As you can see, the current is at an unacceptable
2.5 amps.
It is easy to find out which individual injector is at fault.
All you need to do is inductively clamp onto each individual injector
and compare them. To obtain a known-good value to compare against, we
used the good bank to capture the waveform in Fig. 6. Notice that it
limits current flow to 750 milliamps.
The waveform shown in Fig. 7 illustrates the problem injector
we found. This waveform indicates an unacceptable current draw of just
over one amp as compared to the 750 milliamp draw of the known-good
injector. A subsequent check with a DVOM found 8.2 ohms, which is
under the 12 ohm specification.
Fig. 4: Injector Bank w/Normal Current Flow - Current Pattern
Application Front - In. (mm) Rear - In. (mm\
)
Gas Engine With
14" & 15" Wheels (1) ....... 29.04-29.82
(737.5-757.5) .......... 29.76-30.54\
(756.0-776.0)\
Gas Engine With 15",
16" & 17" Wheels ( 2) ....... 29.27-30.05
(743.5-765.5) ........... 30.0-30.78\
(762.0-782.0)\
CNG & Electric Vehicles ..... 30.46-31.24
(783.5-803.5) ........... 31.2-31.98\
(792.5-812.5)\
( 1) - With tire sizes P205/75R 15 and P215/65R 15.
( 2) - With tire sizes P215/70R 15, P215/65R 16 and 215/65R 17.
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HOIST
CAUTION: On Ram Van/Wagon, ensure there is adequate drive shaft
clearance while raising vehicle. DO NOT raise vehicle by
hoisting or jacking against front lower control arms. If rear
axle, fuel tank, spare tire and liftgate will be removed for
service, place additional weight on rear end of vehicle. This
will prevent tipping as center of gravity changes.
Caravan, Ram Van/Wagon, Town & Country, & Voyager
To raise vehicle on single and twin post type hoists, ensure
hoist pads contact vehicle frame behind front control arm pivots and
inside rear wheels on rear axle housing. Always use hoist adapters.
See Fig. 2 or 5.
Dakota & Ram Pickup
Vehicle may be raised on single or twin post swiveling arm,
or ramp-type drive hoists. If using swiveling arm hoist, ensure
lifting arms, pads or ramps are positioned evenly on frame rails, and
adequate clearance is maintained for transfer case (4WD models) or
skid plate. All hoists must be equipped with adapters to properly
support vehicle. See Fig. 3.
WHEEL ALIGNMENT PROCEDURES
FRONT WHEEL CAMBER & CASTER ADJUSTMENT
CAUTION: DO NOT adjust caster by heating or bending suspension
components. If caster angle is incorrect, replace
component(s) causing incorrect angle.
Caravan, Town & Country, & Voyager
1) Caster is factory preset and cannot be adjusted. Camber is
factory preset, but can be adjusted with a camber service kit. Raise
and support vehicle. While holding lower strut attaching bolts
stationary, loosen attaching nuts. See Fig. 6. Remove upper attaching
nut and bolt. Install camber service kit attaching/adjusting bolt and
nut. While holding bolt stationary, lightly tighten nut. Repeat
procedure for lower attaching nut and bolt.
2) Lower vehicle until vehicle weight is supported by
suspension. Bounce vehicle several times and allow suspension to
settle. Rotate new cam bolt to move top of wheel in or out to
specified camber. See WHEEL ALIGNMENT SPECIFICATIONS table. Tighten
through-bolt nuts to specification. See TORQUE SPECIFICATIONS table.