
Fig. 16: Cutaway View Of Typical Integrated Electronic EGR Valve
Courtesy of GENERAL MOTORS CORP.
SPARK CONTROLS (SPK)
Spark control systems are designed to ensure the air/fuel mixture is ignited at the best possible moment to provide optimum efficiency and
power and cleaner emissions.
Ensure vacuum hoses to the distributor, carburetor, spark delay valves, thermal vacuum switches, etc., are in place and routed properly. On
Computerized Engine Controls (CEC), check for presence of required sensors (O2, MAP, CTS, TPS, etc.). Ensure they have not been
tampered with or modified.
Check for visible modification or replacement of the feedback carburetor, fuel injection unit or injector(s) with a non-feedback carburetor or
fuel injection system. Check for modified emission-related components unacceptable for use on pollution-controlled vehicles.
AIR INJECTION SYSTEM (AIS)
Air Pump Injection System (AP)
The air pump is a belt-driven vane type pump, mounted to engine in combination with other accessories. The air pump itself consists of the
pump housing, an inner air cavity, a rotor and a vane assembly. As the vanes turn in the housing, filtered air is drawn in through the intake port
and pushed out through the exhaust port. See Fig. 17
.
Check for missing or disconnected belt, check valve(s), diverter valve(s), air distribution manifolds, etc. Check air injection system for proper
hose routing.
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Fig. 17: Typical Air Pump Injection System
Courtesy of GENERAL MOTORS CORP.
Pulsed Secondary Air Injection (PAIR) System
PAIR eliminates the need for an air pump and most of the associated hardware. Most systems consists of air delivery pipe(s), pulse valve(s) and
check valve(s). The check valve prevents exhaust gases from entering the air injection system. See Fig. 18
.
Ensure required check valve(s), diverter valve(s), air distribution manifolds, etc., are present. Check air injection system for proper hose
routing.
Fig. 18: Typical Pulsed Secondary Air Injection System
Courtesy of GENERAL MOTORS CORP.
OXYGEN SENSOR (O2)
The O2 sensor is mounted in the exhaust system where it monitors oxygen content of exhaust gases. Some vehicles may use 2 O2 sensors. The
O2 sensor produces a voltage signal which is proportional to exhaust gas oxygen concentration (0-3%) compared to outside oxygen (20-21%).
This voltage signal is low (about .1 volt) when a lean mixture is present and high (1.0 volt) when a rich mixture is present.
As ECM compensates for a lean or rich condition, this voltage signal constantly fluctuates between high and low, crossing a reference voltage
supplied by the ECM on the O2 signal line. This is referred to as cross counts. A problem in the O2 sensor circuit should set a related trouble
code.
COMPUTERIZED ENGINE CONTROLS (CEC)
The CEC system monitors and controls a variety of engine/vehicle functions. The CEC system is primarily an emission control system designed
to maintain a 14.7:1 air/fuel ratio under most operating conditions. When the ideal air/fuel ratio is maintained, the catalytic converter can
control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.
The CEC system consists of the following sub-systems: Electronic Control Module (ECM), input devices (sensors and switches) and output
signals.
EARLY FUEL EVAPORATION (EFE)
The EFE valve is actuated by either a vacuum actuator or a bimetal spring (heat-riser type). The EFE valve is closed when engine is cold. The
closed valve restricts exhaust gas flow from the exhaust manifold. This forces part of the exhaust gas to flow up through a passage below the
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carburetor. As the exhaust gas quickly warms the intake mixture, distribution is improved. This results in better cold engine driveability,
shorter choke periods and lower emissions.
Ensure EFE valve in exhaust manifold is not frozen or rusted in a fixed position. On vacuum-actuated EFE system, check EFE thermal vacuu
m
valve and check valve(s). Also check for proper vacuum hose routing. See Fig. 19
.
Fig. 19: Typical Vacuum
-Actuated EFE System
Courtesy of GENERAL MOTORS CORP.
EMISSION MAINTENANCE REMINDER LIGHT (EMR)
If equipped, the EMR light (some models may use a reminder flag) reminds vehicle operator that an emission system maintenance is required.
This indicator is activated after a predetermined time/mileage.
When performing a smog check inspection, ensure EMR indicator is not activated. On models using an EMR light, light should glow when
ignition switch is turned to ON position and should turn off when engine is running.
If an EMR flag is present or an EMR light stays on with engine running, fail vehicle and service or replace applicable emission-related
components. To reset an EMR indicator, refer to appropriate MAINTENANCE REMINDER LIGHTS article in GENERAL INFORMATION.
MALFUNCTION INDICATOR LIGHT (MIL)
The Malfunction Indicator Light (MIL) is used to alert vehicle operator that the computerized engine control system has detected a
malfunction (when it stays on all the time with engine running). On some models, the MIL may also be used to display trouble codes.
As a bulb and system check, malfunction indicator light will glow when ignition switch is turned to ON position and engine is not running.
When engine is started, light should go out.
Copyr ight 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.
Article GUID: A00130226
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Back To Article
GENERAL INFORMATION
Engine Perform ance Diagnostic Routine Outline
* PLEASE READ THIS FIRST *
WHERE DOES DRIVEABILITY DIAGNOSIS START?
PERFORM BASIC INSPECTION
1. Verify Customer Complaint
2. Perform Visual Inspection (See Basic Diagnostic Procedures)
3. Test Engine Sub-Systems (See Basic Diagnostic Procedures)
Mechanical Condition (Compression)
Ignition Output
Fuel Delivery
4. Check Air Induction System For Leaks
5. Check & Adjust Basic Engine Settings(See On-Vehicle Adjustments)
Ignition Timing
Idle Speed
CHECK FOR TROUBLE CODES
1. Check for Diagnostic Trouble Codes (DTCs).(See Self-Diagnostics)
2. Repair cause of DTCs.
3. Clear PCM memory and repeat self-test.
DIAGNOSE SYMPTOM
1. If no self-diagnostics available, or no trouble codes present, identify symptom.
2. See trouble shooting procedure to identify problem. (See Trouble Shooting - No Codes)
TEST SYSTEM
1. Perform required tests. (See Systems & Component Testing)
2. Verify complaint is repaired. NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
Copyr ight 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.
Article GUID: A00002341
Page 1 of 1 MITCHELL 1 ARTICLE - GENERAL INFORMATION Engine Performance Diagnostic Routine Outline
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SERVICE & ADJUSTMENT SPECIFICATIONS
If you want a specification quickly, this is the place to look. Instead of hunting through a long article, we've separated out the important
specifications and arranged them into easy-to-use tables in a centralized location. You can find valuable information like spark plug wire
resistance, valve clearance, timing, firing orders, etc.
ADJUSTMENT
ON-VEHICLE ADJUSTMENTS
The ON-VEHICLE ADJUSTMENTS article contains the type of information that was previously thought of as TUNE-UP information.
Procedures for checking and adjusting valves, base ignition timing and idle speed are found in this section. Use this section in conjunction with
SERVICE & ADJUSTMENT SPECIFICATIONS for performing routine maintenance. Also, if you have a driveability problem, ensure all on-
vehicle adjustments are within specification before attempting further diagnosis.
THEORY & OPERATION
This article covers basic THEORY & OPERATION of engine performance-related systems and components. Before diagnosing vehicles or new
systems with which you are not completely familiar, read this article.
TESTING & DIAGNOSTICS
BASIC DIAGNOSTIC PROCEDURES/BASIC TESTING
The procedures listed in this article can help you avoid skipping a simple step early, like checking base timing, which could be costly in both
time and money later. This is also a potential starting point for diagnosis of a "no-start" condition. If all systems check out okay here, proceed
to SELF-DIAGNOSTICS/TESTS W/CODES or TROUBLE SHOOTING - NO CODES/TESTS W/O CODES article.
SELF-DIAGNOSTICS/TESTS W/CODES
Use this information to retrieve and interpret Diagnostic Trouble Codes (DTCs) accessed from the vehicle's self-diagnostic system. Once
information is retrieved, manufacturer diagnostic procedures are given to help pinpoint and repair computer system/component faults. Also
included are steps for clearing trouble codes once these faults are repaired. If there is a driveability symptom with no trouble codes set,
proceed to TROUBLE SHOOTING - NO CODES/TESTS W/O CODES article.
TROUBLE SHOOTING - NO CODES/TESTS W/O CODES
This is where to go when you have a problem that does not set a trouble code. It can help determine cause of problem using driveability
symptoms and intermittent testing procedures. Procedures in this information should lead you to a specific component or system test.
SYSTEM & COMPONENT TESTING
Here you will find various tests for engine performance systems and their components, such as air induction (turbochargers and superchargers),
fuel control, ignition control and emission systems.
PIN VOLTAGE CHARTS
These are supplied (when available from manufacturer) to quicken the diagnostic process. By checking pin voltages at the Powertrain Control
Module (PCM), you can determine if the PCM is receiving and/or transmitting proper voltage signals. Pin charts may also be referred to as PID
charts by some manufacturers.
SENSOR RANGE CHARTS
SENSOR OPERATING RANGE CHARTS
These are supplied (when available from manufacturer) to determine if a sensor is out of calibration. An out-of-calibration sensor may not set a
trouble code, but it may cause driveability problems.
VACUUM DIAGRAMS
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
Page 2 of 3 MITCHELL 1 ARTICLE - GENERAL INFORMATION How To Use The Engine Performance Section - 1989 & Newer Models
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Back To Article
GENERAL INFORMATION
Parasitic Load Explanation & T est Procedures
* PLEASE READ THIS FIRST *
GENERAL INFORMATION
The term Parasitic Load refers to electrical devices that continue to use or draw current after the ignition switch is turned to OFF position. This
small amount of continuous battery draw is expressed in milliamps (mA). On Chrysler vehicles, a typical Parasitic Load should be no more
than 30 milliamps (0.030 amps). On Ford Motor Co. and General Motors vehicles produced after 1980, a typical Parasitic Load should be no
more than 50 milliamps (0.050 amps).
Vehicles produced since 1980 have memory devices that draw current with ignition off for as long as 20 minutes before shutting down the
Parasitic Drain. When Parasitic Load exceeds normal specifications, the vehicle may exhibit dead battery and no-start condition.
Follow test procedure for checking Parasitic Loads to completion. A brief overview of a suggested test procedure is included along with some
typical Parasitic Load specifications. Refer to GENERAL MOTORS PARASITIC LOAD TABLE chart.
TESTING FOR PARASITIC LOAD
The battery circuit must be opened to connect test switch (shunt) and ammeter into the circuit. When a battery cable is removed, timer circuits
within the vehicle computer are interrupted and immediately begin to discharge. If in doubt about the condition of the ammeter fuse, test it
with an ohmmeter prior to beginning test. An open fuse will show the same reading (00.00) as no parasitic drain. Begin test sequence with the
meter installed and on the 10-amp scale. Select lower scale to read parasitic draw.
CHRYSLER IGNITION OFF DRAW (IOD) TEST
To test for excessive IOD, verify that all electrical accessories are OFF. Turn off all lights, remove ignition key, and close all doors and decklid.
If the vehicle is equipped with electronic accessories (illuminated entry, automatic load leveler, body computer, or high line radio), allow the
system to automatically shut off (time out), up to 3 minutes.
1. Raise the hood and disconnect both battery cables, negative first.
2. Reconnect the negative cable and connect a typical 12-volt test light (low wattage bulb) between the positive cable clamp and the
positive battery post. Remove the engine compartment lamp bulb. If the test light does not light, proceed to step 3
. If the test light does
light, proceed to step, 4
. The test light will indicate IOD greater than 3 amps. After higher amperage IOD has been corrected, proceed to
step 3
.
3. ith 12-volt test light still connected (not lit), connect an ammeter (milliampere scale) between the positive cable clamp and the positive
battery post, disconnect test light, refer to instructions provided with ammeter being used. A reading of 30 milliamperes or less indicates
normal electrical draw. If ammeter reads more than 30 milliamperes, excessive IOD must be corrected.
4. Locate the fuse panel and remove fuses or circuit breakers one at a time, and observe ammeter after each fuse or circuit breaker is
removed. If test light goes out and the reading drops below 30 milliamperes when a certain fuse or circuit breaker is removed, that circuit
may have a defect.
5. If IOD is detected after all fuses and circuit breakers have been removed, disconnect the 60-way connector at the Single Module Engine
Control (SMEC), located outboard of the battery.
6. If excessive IOD is detected after all fused circuits and SMEC have been verified, disconnect the B+ terminal from the alternat o r. If
reading drops below 30 milliamperes, reinstall all fuses and circuit breakers, reconnect B+ terminal at alternator, reconnect battery, and
perform alternator diagnostics.
7. Install engine compartment lamp bulb.
TEST PROCEDURE USING TEST SWITCH
1. Turn ignition off. Remove negative battery terminal cable. Install Disconnect Tool (J-38758) test switch male end to negative battery
cable. Turn test switch knob to OFF position (current through meter). Install negative battery cable to the female end of test switch. NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. For m odel-specific inform ation see appropriate articles where
available.
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. For m odel-specific inform ation see appropriate articles where
available.
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. For m odel-specific inform ation see appropriate articles where
available.
CAUT ION: Always turn ignition off when connecting or disconnecting battery cables, battery chargers or jum per
cables. DO NOT turn test switch to OFF position (which causes current to run through am m eter or
vehicle electrical system ).
NOTE:Mem ory functions of various accessories m ust be reset after the battery is reconnected.
CAUT ION: IOD greater than 3 am ps m ay dam age m illam pm eter.
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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 ge t s "a ve r a ge d o u t ", c a u sin g yo u t o 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 but it cannot figure out
the throttling action. In other words, it cannot distinguish the throttling from an open circuit (de-energized) condition.
Yet current controlled injectors will still yield a millisecond on-time reading on these DVOMs. You will find it is also always the same,
regardless of the operating conditions. This is because it is only measuring the initial completely-closed circuit on-time, which always takes the
same amount of time (to lift the injector pintle off its seat). So even though you get a reading, it is useless.
The second limitation is that a few erratic conditions can cause inaccurate readings. This is because of a DVOM's slow display rate; roughly
two to five times a second. As we covered earlier, measurements in between display updates get averaged. So conditions like skipped injector
pulses or intermittent long/short injector pulses tend to get "averaged out", which will cause you to miss important details.
The last limitation is that varying engine speeds can result in inaccurate readings. This is caused by the quickly shifting injector on-time as the
engine load varies, or the RPM moves from a state of acceleration to stabilization, or similar situations. It too is caused by the averaging of all
measurements in between DVOM display periods. You can avoid this by checking on-time when there are no RPM or load changes.
A lab scope allows you to overcome each one of these limitations.
Checking Injector On-Time With Dwell Or Duty
If no tool is available to directly measure injector millisecond on-time measurement, some techs use a simple DVOM dwell or duty cycle
functions as a replacement.
While this is an approach of last resort, it does provide benefits. We will discuss the strengths and weaknesses in a moment, but first we will
look at how a duty cycle meter and dwell meter work.
How A Duty Cycle Meter and Dwell Meter Work
All readings are obtained by comparing how long something has been OFF to how long it has been ON in a fixed time period. A dwell meter
and duty cycle meter actually come up with the same answers using different scales. You can convert freely between them. See
RELATIONSHIP BETWEEN DWELL & DUTY CYCLE READINGS TABLE
.
The DVOM display updates roughly one time a second, although some DVOMs can be a little faster or slower. All measurements during this
update period are tallied inside the DVOM as ON time or OFF time, and then the total ratio is displayed as either a percentage (duty cycle) or
degrees (dwell meter).
For example, let's say a DVOM had an update rate of exactly 1 second (1000 milliseconds). Let's also say that it has been measuring/tallying
an injector circuit that had been ON a total of 250 mS out of the 1000 mS. That is a ratio of one-quarter, which would be displayed as 25%
duty cycle or 15° dwell (six-cylinder scale). Note that most duty cycle meters can reverse the readings by selecting the positive o r n e ga t ive
slope to trigger on. If this reading were reversed, a duty cycle meter would display 75%.
Strengths of Dwell/Duty Meter
The obvious strength of a dwell/duty meter is that you can compare injector on-time against a known-good reading. This is the only practical
way to use a dwell/duty meter, but requires you to have known-good values to compare against.
Another strength is that you can roughly convert injector mS on-time into dwell reading with some computations.
A final strength is that because the meter averages everything together it does not miss anything (though this is also a severe weakness that we
will look at later). If an injector has a fault where it occasionally skips a pulse, the meter registers it and the reading changes accordingly.
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![FORD FESTIVA 1991 Service Manual
Fig. 7: Single Injector w/Excessive Current Flow
- Current Pattern
EXAMPLE #2 - VOLTAGE CONTROLLED DRIVER
This time we will look at a GM 3.1L V6 VIN [T]. Fig. Fig. 8
shows the 1, 3, 5 (odd) inje FORD FESTIVA 1991 Service Manual
Fig. 7: Single Injector w/Excessive Current Flow
- Current Pattern
EXAMPLE #2 - VOLTAGE CONTROLLED DRIVER
This time we will look at a GM 3.1L V6 VIN [T]. Fig. Fig. 8
shows the 1, 3, 5 (odd) inje](/manual-img/11/56935/w960_56935-290.png)
Fig. 7: Single Injector w/Excessive Current Flow
- Current Pattern
EXAMPLE #2 - VOLTAGE CONTROLLED DRIVER
This time we will look at a GM 3.1L V6 VIN [T]. Fig. Fig. 8
shows the 1, 3, 5 (odd) injector bank with the current waveform indicating about
a 2.6 amp draw at idle. This pattern, taken from a known good vehicle, correctly stays at or below the maximum 2.6 amps current range.
Ideally, the current for each bank should be very close in comparison.
Notice the small dimple on the current flow's rising edge. This is the actual injector opening or what engineers refer to as the "set p o in t . " Fo r
good idle quality, the set point should be uniform between the banks.
When discussing Ohm's Law as it pertains to this parallel circuit, consider that each injector has specified resistance of 12.2 ohms. Since all
three injectors are in parallel the total resistance of this parallel circuit drops to 4.1 ohms. Fourteen volts divided by four ohms would pull a
maximum of 3.4 amps on this bank of injectors. However, as we discussed in EXAMPLE #1
above, other factors knock this value down to
roughly the 2.6 amp neighborhood.
Now we are going to take a look at the even bank of injectors; injectors 2, 4, and 6. See Fig. 9. Notice this bank peaked at 1.7 amps at idle as
compared to the 2.6 amps peak of the odd bank (Fig. Fig. 8
). Current flow between even and odd injectors banks is not uniform, yet it is not
causing a driveability problem. That is because it is still under the maximum amperage we figured out earlier. But be aware this vehicle could
develop a problem if the amperage flow increases any more.
Checking the resistance of this even injector group with a DVOM yielded 6.2 ohms, while the odd injector group in the previous example read
4.1 ohms.
Fig. 8: Injector Odd Bank w/Normal Current Flow
- Current Pattern
Fig. 9: Injector Even Bank w/Normal Current Flow
- Current Pattern
EXAMPLE #3 - VOLTAGE CONTROLLED DRIVER
Example #3 is of a Ford 5.0L V8 SEFI. Fig. Fig. 10
shows a waveform of an individual injector at idle with the Lab Scope set on 200
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