Question about 1998 Chevrolet S-10 Pickup

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Re: diagram for location of ECM (Engine Control Module) not specifically identified

I checked your solution at the AutoZone site. Closest I come to the ECM is
the ICM (Ignition Control Module) at following link:

I'm not sure that the ICM is actually the ECM. The ECM (Engine Control Module), I believe, controls much more than the ignition timing but also fuel mixture at various RPMs and loads. I just can't seem to locate any schematics or specific information on the AutoZone site that describes the ECM. I need a diagram specific for the ECM since I am researching a reprogramming of the ECM by a company out of MT (PowerUpDiesel) that will set up my vehicle's ECM computer to provide the most efficient metering of fuel for increased power and fuel efficiency, specific to my vehicle (i.e., I provide my ECM with VIN # and tire size and they reprogram the module more accurately than the manufacturer's stock program).

I may need to just go down to my local Chevrolet dealer and get the information but thought that I could save myself a trip by getting advice from others here
RB in Anchorage

Posted by reburnside on


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Anand Kumar

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Well i searched this link all got was this information hope it helps you :

Good luck..

Posted on Aug 18, 2008


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    Idle fluxuates up and down consistantly

    Check the Idle Control System

    Idle speed is controlled by the Idle Air Control Valve (IACV). The IACV changes the amount of air being bypassed to the intake manifold, in response to electric current controlled by the ECM. When the IACV is activated, the valve opens to maintain proper idle speed.

    Symptom and Subsystems to Check:

    1. Difficult to start engine, when cold--check Fast Idle Thermo Valve.

    2. Fast idle out of spec, when cold:
    a. Check Fast Idle Thermo Valve.
    b. Check IACV.
    c. Check idle adjusting screw (see Section C).

    3. Rough idle:
    a. Check hoses and connections.
    b. Check IACV.

    4. RPM too high, when warm:
    a. Check IACV.
    b. Check Fast Idle Thermo Valve.
    c. Check hoses and connections, check Power Steering Pressure Switch Signal, and check idle adjusting screw.

    5. RPM too low, when warm:
    a. Idle speed is below specified rpm, with no load--check IACV and idle adjusting screw.
    b. Idle speed doesn't increase after initial start up--check IACV.
    c. Idle speed drops in gear (automatic transmission)--check automatic transaxle gear position switch signal.
    d. Idle speed drops when AC is on--check air conditioning signal and IACV.
    e. Idle speed drops when steering wheel is turned--check power steering pressure switch signal and IACV.
    f. Idle speed fluctuates with electrical load--check hoses and connections, IACV, and Alternator FR Signal.

    6. Frequent stalling, while warming up--check IACV and idle adjusting screw.

    7. Frequent stalling, after warming up--check idle adjusting screw and IACV.

    Additional Steps:

    . Check Alternator FR Signal. Have alternator inspected, if idle speed fluctuates with electrical load. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD. This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy.

    . Clean main ECM ground on thermostat housing.

    . Reset ECM, by removing the 7.5 amp Back Up Fuse, in the under-hood fuse box, for 10 seconds.

    . Replace PCV Valve, cleaning hose with brake cleaner spray.

    . Substitute a known-good ECM. If symptom goes away, replace original ECM.

    Check the ICM (Erratic RPM and PGM-FI System)

    When the engine is cold, the air conditioner compressor is on, the transmission is in gear (automatic transmission only) or the alternator is charging, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. Here's an overview of how the PGM-FI System works.


    Various inputs to the ECM are TDC/CKP/CYP Sensor, MAP Sensor, ECT Sensor, IAT Sensor, TP Sensor, HO2S, VSS, BARO Sensor, EGR Valve Lift Sensor, Starter Signal, Alternator FR Signal, Air Conditioning Signal, Automatic Transmission Shift Position Signal, Battery Voltage (Ignition 1) Brake Switch Signal, PSP Switch Signal, ELD, and VTEC Pressure Switch.

    Inputs are received and processed by the ECM's Fuel Injector Timing and Duration, Electronic Idle Control, Other Control Functions, Ignition Timing Control, and ECM Back-up Functions. These are the primary functional areas within the ECM.

    Outputs from the ECM control Fuel Injectors, PGM-FI Main Relay (Fuel Pump), MIL (Check Engine Light), Idle Air Control (IAC) Valve, A/C Compressor Clutch Relay, Ignition Control Module (ICM), EVAP Purge Control Solenoid Valve, HO2S Heater, EGR Control Solenoid Valve, Alternator, Lock-up Solenoid Valve A/B (A/T), VTEC Solenoid Valve, and Interlock Control Unit.

    Idle RPM:

    Once you understand how the PGM-FI system is configured, it's easy to see how the ECM, Idle Air Control Valve, and the Ignition Control Module affect idle rpm. If the ECM's Electronic Idle Control function is not working properly, then it cannot properly control the IAC Valve. Likewise, if the ECM's Ignition Timing Control function is not operating properly, it cannot properly control the ICM (igniter). Obviously, idle rpm will also be affected if there's a problem with the IAC Valve or the ICM. As stated above, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. This cannot happen if the IAC Valve is failing. The same situation exists if the ICM is failing. The ECM will tell the ICM to open and close the primary voltage circuit going to the coil and it won't respond properly. The result will be erratic spark plug firing and erratic rpm.


    If you are experiencing erratic idle rpm, try and isolate whether the problem is caused by the ICM (ignitor), IAC Valve, or the ECM. My experience has been that a failing ICM is usually responsible for the problem. Keep in mind that tachometers are connected directly to the ICM. Therefore, a fluctuating tachometer needle is often a dead giveaway. Heat and poor preventive maintenance (causing high secondary voltage to be discharge on internal distributor components) frequently causes the ICM (and coil) to fail. Besides performance, this is another reason why it's important to regularly replace spark plugs, spark plug wires, rotors, and distributor caps. Electricity will always follow the path of least resistance, even if it isn't the intended one. Our job is to ensure the intended path is the path of least resistance.

    Ignitor (ICM) and Coil Replacement:

    1. Disconnect negative battery cable.
    2. Remove hex head machine screws, securing distributor cap to housing, using an 8 mm nut driver.
    3. Move distributor cap and wires off to the side.
    4. Remove machine screw securing rotor to shaft, using a #2 Phillips head screwdriver. It may be necessary to "hit" the starter once or twice, in order to rotate rotor for access to mounting screw.
    5. Remove rotor and leak cover.
    6. Unfasten ignitor wires, remove coil mounting screws, and set coil aside. Note: Removing coil first improves access to igniter.
    7. Unfasten screws securing igniter to housing.
    8. Remove ignitor from distributor and unfasten screws mounting ignitor to heat sink.
    9. Coat back of new ignitor (or old igniter, if reusing) and male connectors with silicone grease. Silicone grease increases heat transfer to heat sink. Failure to apply silicone grease will cause the ignitor to quickly fail.
    10. Mount ignitor to heat sink and reinstall ignitor, igniter terminal wires, coil, coil wires, leak cover, rotor, and distributor cap. Ensure female ignitor terminals fit snugly--crimp with pliers, if necessary.

    AutoZone can test ICMs and coils for free. If you plan to keep the car, I would replace the ICM due the age of your Civic.

    Sep 15, 2010 | 1991 Honda Civic

    1 Answer


    Have you tried the following:

    Ignition Control Module (ICM) REMOVAL & INSTALLATION NOTE: Only the EEC-IV ignition systems use an external ICM. EEC-V systems have incorperated the ICM into the Power Control Module (PCM).
    1. Disconnect the negative battery cable.
    2. Detach the wiring harness connector(s) from the ICM.
    3. Remove the mounting bolts, then remove the ICM. To install:
    4. Position the ICM onto the inner fender apron and install the mounting bolts. Tighten the bolts to 22–31 inch lbs (2.5–3.5 Nm).
    5. Attach the wiring harness connector(s) to the ICM.
    6. Connect the negative battery cable. Fig. 1: Ignition control module and mounting location on the 2.3L, 2.5L engine 89682g32.gif
      Fig. 2: Ignition control module used on all EEC-IV systems except the 2.3L engine 89682g33.gif
      Fig. 3: Ignition control module mounting on all EEC-IV systems except the 2.3L engine 89682g34.gif
    prev.gif next.gif

    Jul 11, 2010 | 1996 Ford Explorer

    1 Answer

    How do you remove the ignition coil

    Each ignition control module (ICM) has the following circuits:
    An ignition 1 voltage circuit A chassis ground An ignition control circuit for each cylinder A low reference circuit
    The PCM controls spark by pulsing the ignition control circuits to the ICM to trigger the coils and fire the spark plugs. The PCM and ICM are internally protected against shorts to power and ground on the ignition control circuits.

    The spark plugs are connected to each coil by a short boot. The boot contains a spring that conducts the spark energy from the coil to the spark plug. The spark plugs are tipped with platinum for long wear and higher efficiency.

    Ignition Control Module (ICM) Connectors


    Fig. Ignition coil locations 2001-2004 4.8L, 5.3L, 6.0L Engines

    Removal & Installation
    2.2L (L61) Engine
    1. Turn OFF the ignition.
    2. Remove the accelerator cable from the bracket.
    3. Remove the accelerator cable bracket bolt.
    4. Remove the accelerator cable bracket.
    5. Disconnect the ignition control module (ICM) harness connector.
    6. Remove the ICM retaining screws.
    7. Remove the ICM from the ignition coil housing.

    To install:
    1. Install the ignition control module in the ignition coil housing.
    2. Install the ICM retaining screws. Tighten the retaining screws.
    3. Connect the ICM harness connector.
    4. Install the accelerator cable bracket.
    5. Install the accelerator cable bracket bolt. Tighten the retaining screws.
    6. Install the accelerator cable to the bracket.

    2.2L (Ln2) Engine
    1. Remove the air cleaner outlet from the air cleaner.
    2. Remove the ICM electrical connectors (1) and spark plug wires (2).
    3. Remove the ignition coils bolts (3).
    4. Remove the ignition coils and ICM assembly.
    5. Installation is the reverse of the removal procedure.

    2.4L Engine
    1. Disconnect the negative battery cable.
    2. Remove the accelerator cable from the hold down clip.
    3. Remove the cruise control cable, if applicable.
    4. Remove the bolt from the fuel line retaining clip.
    5. Disconnect the 11-pin harness connector for the ignition control module (ICM).
    6. Remove the bolts from the ignition coil and the ICM assembly-to-camshaft housing.
    7. Remove the ignition coil and ICM assembly from the engine.
    8. Remove the screws that retain the housing to the cover.
    9. Disconnect the coil harness connector from the ICM.
      CAUTION When removing the housing from the cover, make sure the ground strap stays in place.
    10. Remove the housing from the cover.
    11. Remove the screws that retain the ICM to the cover.
    12. Remove the ICM from the cover.

      Fig. Removing the ICM from the camshaft cover

    To install:

    CAUTION DO NOT wipe grease from the module or coil if the same module is to be replaced. If a new module is to be installed, a package of silicone grease will be included with the module. Spread the grease on the metal face of the module and on the cover where the module seats. This grease is necessary for module cooling.
    1. Install the ICM to the cover.
    2. Install the screws that retain the ICM to the cover.
    3. Install the ground strap, if necessary.
    4. Connect the ignition coils connector to the ICM.
      CAUTION When installing the housing to the cover, make sure the ground strap stays in place.
    5. Install the housing to the cover.
    6. Install the screws that retain the housing to the cover.
    7. Install the spark plug boots and the retainers to the housing, if necessary.
    8. Install the ICM assembly to the engine while carefully aligning the spark boots to the spark plug terminals.
      CAUTION The ICM cover bolts must be installed using isolator washers with the rubber side facing down.
    9. Install the bolts that retain the ICM assembly to the camshaft housing after coating the bolt threads with LOCTITE, or equivalent. Tighten the bolts to 16 ft. lbs. (22 Nm).
    10. Connect the ICM 11 pin harness connector.
    11. Install the bolt to the fuel line retainer clip.
    12. Install the accelerator cable into the hold down clip.
    13. Install the cruise control cable, if applicable. Connect the negative battery cable.

    Hope this help (remember comment and rated this).

    Apr 05, 2010 | 2000 Chevrolet Blazer

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