Possible ECM/PCM problem 93 TBI 350

Discussion in 'Chevy Truck Forum' started by dk-93silverado, Nov 11, 2009.

  1. dk-93silverado

    dk-93silverado Senior Member

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    #1 dk-93silverado, Nov 11, 2009
    Last edited: Nov 12, 2009
    :help:I have a 93 TBI 350 in a k2500 with a 4l80e. I am diagnosing a potential PCM problem. All grounds at PCM are good. I have battery voltage at PCM also. I notice that the ground side(ecu) of the fuel injector circuit is not operating. Meaning no fuel delivery. With DVOM I verified battery voltage at both injectors. When I ground the injectors via wire to ground they deliver fuel with key on. The ignition system is operating. MAP and TPS have 5 volt reference voltage, ground and correct signal going back for a key on non running condition. Prior to fixing, this truck had an engine bay fire melting the engine wiring harness into a ball of bare wire so I am afraid it could have damaged the ECM. When I removed the case from the PCM I can not detect any burnt components or any sign of damage what so ever. FYI I did completely customize a 94 harness to work in this truck so there is the possibility of wiring issues but every pin going to the PCM goes where it is supposed to on both ends. PCM terminal D1(battery feed) and C1(ignition fused) both have battery voltage with key on. Does anyone have any advise? I assume these ECM's have injector divers. If anyone has any info I would appreciate it. Thank you in advance. :idea: =:applaud:
     
  2. dk-93silverado

    dk-93silverado Senior Member

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    #2 dk-93silverado, Nov 11, 2009
    Last edited: Nov 12, 2009
    I also wanted to add that I am using the PCM from the 93 and all sensors from the 93 as well just to clarify. There is a new pick up coil and ignition control module also. I wanted to provide as much info as possible. The only other thing acting strange is that I have no power going to the starter solenoid when turning key yet. I am tracing down the path of voltage as we speak. I only mention this because it could be influential in this investigation. I would appreciate anyone's time. Thank you. :)
     
  3. silverhairdeere

    silverhairdeere Senior Member

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    if you have fuel to the injectors with a different ground , that's your problem , somewhere along the wiring it's lost it's ground (short) try a multimeter .also if you have access to a different ecm try that . jmop and probably wrong .

    shd
     
  4. dk-93silverado

    dk-93silverado Senior Member

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    #4 dk-93silverado, Nov 11, 2009
    Last edited: Nov 12, 2009
    They are actuated by the PCM on the ground side of the circuit to operate in a normal situation. They currently have continuity with the PCM but the circuit is not completed by the PCM. This is why I am suspecting a possible PCM issue.
     
  5. dk-93silverado

    dk-93silverado Senior Member

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    You are correct. This loss of grounding ability is why the injectors are not operating. I just want to verify the cause of this and I know via DVOM continuity check that the wires have connection to the correct ECM terminals. Thank you for suggestion. I'll take anything I can get bro.
     
  6. dk-93silverado

    dk-93silverado Senior Member

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    Does anyone have a picture of the injector drivers in a early 90's TBI ECM?
     
  7. crabtruck

    crabtruck Senior Member

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    Not too sure what you are looking for in the way of "inj drivers"
    I will tell you that the ECM has internal fault protection
    that acts somewhat like load drivers. They may be active
    at this time from a external wiring fault: short to hot,gnd,elsewhere.

    ECM does not "ground" the injectors, it pulses them to control volume.
    Measuring that can be a bit of a trick with home supplies.
    ECM may not be trying to send the inj pulses for a number of reasons.
    It does not like losing it's ign ref or it's VSS signal.

    Assuming the ECM is good based on a visual inspection
    is only good for checking for attacks by mice. Static and
    reversed polarities are invisible and deadly.

    Ask the ECM. Pull codes.

    On the no voltage to starter thing, do a search of threads, good info.
     
  8. dk-93silverado

    dk-93silverado Senior Member

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    Thanks I got the no starter solenoid actuation fixed thats not something I was worried about. I just mentioned it to provide as much info as possible. I guess I was just using misleading terminology when it comes to the fuel injector circuit. I understand the pulsing of the injectors I was just kinda referring to the fact that it does so on the ground side of the circuit. Sometimes on a Mitsubishi ECU for instance I have been able to see a damaged injector driver just by looking at it. It's a very common problem with those. That's why I was wondering if this ECM has a similar driver. I work in an automotive repair facility and have node lights in my tool box but currently am without scanner that would have capabilities of directly monitoring this circuit. I know the ECU is getting the ignition reference but I'll have to double check the VSS buffer signal. My information from all data indicates lack of VSS causing harsh shifts but dosn't mention it causing this. Do you think lack of or poor signal could cause the lack of injector actuation? I appreciate your time here I think my poor terminology was misleading. I am aware visual inspection of electrical components is inadequate and this is why I haven't ruled out ECM damage. Before doing anything with the ECM Ill be verifying my VSS to it. Do you by any chance know off hand what value I should expect in a key on engine off scenario testing VSS from VSS buffer? I'll go over all my circuits again throughout the harness to verify nothing is incorrect. I really appreciate that you are taking the time to read my post and respond. I hope I don't come across as argumentative or unappreciative.
     
  9. dk-93silverado

    dk-93silverado Senior Member

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    "I will tell you that the ECM has internal fault protection
    that acts somewhat like load drivers."

    I will have to do my research as to what all can activate internal fault protection. I understand so far that shorts to ground and loss of or incorrect vital input signals can cause this. Thank you for this information I will verify if this is happening or not if possible before I move on.
     
  10. crabtruck

    crabtruck Senior Member

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    You already did it, they will self-reset when problem is removed. :)
    Dirty little secret: ECM uses "quad drivers" meaning four connections in a group.
    The side effect is that a short of one of the four could take down all four.
    Can be aggravating to track that scenario down since no list of sets of four.

    I don't think you're arguementative and I happen to like to "argue" (not fight)
    because it clears thinking by providing the reasons.
    Lifetime avg = 0.25 wins. Pretty good for a married guy.

    You may not have a scantool but you have a paper clip, where's codes ? :)

    If you have the wire from F11 to Ign control mod(D=Wht) grounded/short, then no start.
    If you have the light connector for injectors, you can test Ign mod though
    PCM to Inj process with a test light. Unplug 4-wire on ICmod, turn key on.
    Connect a test light to battery and tap the IC Ref-Hi wire in plug (C=Ppl/Wht).
    Each time "tap" is removed, injector light should flash. Yes means Ign mod problem.
    No flash from Inj after tap says connections back to PCM or PCM bad.

    Since you swapped the harness a thought occurs to me: is it correct?
    I don't have diagrams in front of me but the connection for VSS was
    different depending on MT vs AT, and 4x. PCM got signal direct in some cases,
    through the buffer in others. Something to double check. Possible code 16.

    For the record, and since it might be relevant in your case.
    I tend to use ECM and PCM interchangably but they're not actually.
    With a 5.7 and a 4L80E you should have a PCM. (Likely 93PCM6)
    Only 5.0 and 5.7 with manual trans have ECMs, aka GMCM.
     

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