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Thread: Pcm ground

  1. #21
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    DARREN BRANDON
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    I am at work scanning shoeboxes site, and have yet another question... the dark blue wire that is labeled fuel enable thatbis supposed to be hooked to tdm... I am missing that wire altogether... is that ok? Or do I need to add it and connect it to something?
    Sorry about so many questions, I'm just tired of my car being an garage ornament...

  2. #22
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    If you have a STOCK setup, when you put the key in the lock cylinder, and they key has the correct resistance, the theft deterrent module (TDM) passes 12 volts to the starter relay (TDR) so the starter can crank the engine. At the same time, the TDM sends a 60Hz square wave signal (called the “fuel enable signal”) to the PCM on the dark blue wire. The PCM will not turn on the injectors until it gets that signal

    In your setup, you don’t have a TDM. So you connected 12 volts from the key in the “start” position directly to the starter relay. Then you had Moe delete the requirement for the fuel enable signal. If the PCM was not reprogrammed to delete the requirement or the fuel enable signal, you would have DTC 46.

    The dark blue wire does not need to be connected to anything.

    If the PCM is not receiving the low resolution pulse from the Opti, it will not turn on the injectors, and you will not have any spark.

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  4. #23
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    Didnt get home until late last night, got a few mins to do some tests before I ran out of daylight, its currently looking like the opti or its harness are the issue, more tests this afternoon ( time permitting), hoping it's just the harnesses

  5. #24
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    Ok, it looks like all signs point to the opti, but before I pull it off, I have one more question..

    The 4 wires to the opti, I have 5 volts 5 volts, 12 volts with key on, then on 4th wire, I have a good ground when key is off but when key on, it gets very weak! Is this normal? Or am.i dropping a ground??
    Thanks in advance. Darren

  6. #25
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    Shoebox’s procedure emphasizes the D pin resistance is measured key OFF.

    Follow up with the measurements at the ICM. The 1-4 volts AC on the white wire (pin B) is the key to determining if the Opti low resolution pulse is reaching the PCM and being sent to the ICM to fire the coil.

    Testing the Opti harness with the connector off the Opti just tells you the wiring from the PCM to the Opti is good. To check for the actual pulse signals from the Opti itself, you have to reconnect the harness to the Opti. Then, if all you have is a multi-meter, rotate the Opti slowly, and measure the DC volts at terminal A and B. Easy to do if the Opti isn't installed. As the Opti rotates the voltage should switch back and forth between 0 volts and 5 volts. If you have access to an oscilloscope, you can observe the 0 to 5 volt square wave produced at pins A and B.

  7. #26
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    Thanks, I pulled off the opti, so that test should be easy enough.

  8. #27
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    You will have to run a ground wire from the Opti case to the block.

  9. #28
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    Thanks, glad you mentioned that or I would not have!

  10. #29
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    Ok, I'm at a bit of a loss now, hooked up opti and spun by hand , fuel pump runs, Injectors clicking away... guess my multimeter just doesnt refresh quick enough to test for the pulses.. I do get the 10+ volts on the two wires ar icm, which shoebox says means wiring and coil.is good.. leads me to believe it's the icm? Is my reasoning sound??

  11. #30
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    Turn it SLOWLY. The low res circuit will produce 8 pulse for one revolution of the Opti. There are 4 varying space longer pulses, alternating with 4 short pulses. The high res circuit produces 360 tiny pulses for one rev of the Opti.

    But if the PCM is pulsing the injectors as the Opti rotates, the PCM is receiving the low res pulse.

    The key measurement at the ICM is the 1 to 4 AC volts on the white wire on pin B. That can be checked with the Opti installed and the starter cranking the engine.

    Any decent auto parts store can test the ICM. They need to test it multiple times in sequence to make sure it gets hot. Heat soak can cause intermittent circuit problems.

    Testing for 10+ volts at the ICM verifies the wiring, but not the coil itself.

    http://shbox.com/1/coil_testing.jpg

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