Question about 1998 GMC Jimmy

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Fuel injectors shut off when idling for no reason

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  • highway_sign Oct 02, 2009

    fuel injectors shut off for no reason, condition is worse when cold starting. engine light does not come on even when car stalls until you turn the key 2 or 3 times. changed both sensors

  • highway_sign Oct 06, 2009

    new ecm no result

  • highway_sign Oct 14, 2009

    replaced the pessure regulator, the wiring harness looks good

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  • Master
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HI. I would advise to run a diagnostic scan to insure that there are no stored trouble codes present in the memory of the on-board CPU. IF the scan shows no codes present for extraction, this will confirm that th actual CPU is the culprit. There are only two reasons for this type of shutdown. The first will be ECU/ECM circut damage, and the last issue will be ECM/PCM/ECU wiring harness fault. I would check the entire wiring harness under the hood for worn connections that lead to each vital injector and sensors as well. The sensors to inspect will be the Cam shaft sensor, and the Crankshaft sensor. These two sensors are directly wired to the CPU. If these sensors are malfunctioning, the CPU will shutdown the injectors and fuel pump as well, causing the engine to shutdown. Check each injector housing for worn connectors as well. If the entire CPU harness is in good condition, and all connections and contacts are connected properly, this will confirm that the actual CPU is faulty. Replace the CPU(ECM/PCM/ECU) in this case.

Posted on Oct 02, 2009

  • Michael Masters
    Michael Masters Oct 02, 2009

    Ok, if the engine light is non-functional, this will almost guarantee that the CPU is the issue. The CPU(ECM/PCM/ECU), initiates the illumination of the engine light during diagnostic runs upon engine start up. The CPU, also, controls the sequential ignition timing as well in your vehicle. The CPU is the culprit here.

  • Michael Masters
    Michael Masters Oct 06, 2009

    Ok. the next inspection point will be the actual fuel injector wiring harness. inspect the harness for corroded or loose injector housing contacts. replace the harness if found to be faulty. Insure that the pressure regulator is operating properly as well. If the pressure falls below the threshold, the ecm will shut off the pulse.

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Check your injectors by pulling each injector connector (press clip in the middle and pull connector at the same time).
Then, with a digital voltmeter put the leads on each leg on the injector (they are small so don´t short cut them, plus-minus or minus-plus doesn´t matter).
Engine off and cold they should each measure about 15 to 17 ohms, with a max difference off aprox. 0.5 ohms.
If any are below 10 ohms, they are shot and might be the cause of your cars symptoms.
Another cause might be the EGR system.
Try and read out the computer by jumping the ALDL connector under the IP drivers side bolster over your right knee when sitting in the car.
There are two rows of 6 pins, bend a small paperclip to a U shape and connect the upper right two pins with each other.
Don´t start the car but turn the ignition on only.
If done right, a fan under the hood starts working and the SES light in the center info panel starts blinking.
First time it blinks one short, two long, wich means 12, it does that three times with every code.
If you get the following code: three long, two short, and that three times, you have a problem with your EGR system.
Either the valve is stuck open or shut, or there is a vacuum leak somewhere.
Easy check is to see if there is a vacuum line hanging loose somewhere.

Posted on Oct 02, 2009

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