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Thread: TBI idle surge

  1. #16
    Electronic Ignition!
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  2. #17
    Electronic Ignition!
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  3. #18
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    Does that show CTS and MAP both decreasing? Are you sure all the grounds are correct?

    Generally a problem like this will avoid diagnosis due to some assumption being made. Believeing a pcm is good, or believeing a scan tool is working correctly, believing the non-OEM parts are good because they are new, or believing one test is as good as another are all possible reasons why this problem has lingered so long. The data that's been presented does not lead me to a solution. Although I've asked several questions everything seems to be covered, checked, tested, and determined OK. At this point I usually realize that there's no way for me to find an answer without actually working on the problem myself. There are hundreds of tests a person can devise with ingenuity. Is the MAP reading accurate? An inaccurate reading requires a different set of steps than a valid one. Is CTS actually dropping as the engine runs? Validate the sensor reading with a thermometer. Can you force the readings to be what you want? Removing wires at the ecm and attaching resistors would allow you to tailor the signals if desired. What happens when you feed realistic signals to the ecm? Does the engine run correctly?

    I do not know what further help I can offer. I suspect your harness is not correct but the facts you've given say otherwise. Several sensors have common circuits in an OE application and this may not have been reproduced correctly in this harness. I'm not there to listen to the engine run and to watch the scantool or look at the harness which adds to the challenge. Pictures of scantool are not as good as a video or movie. You say it runs OK but the scan tool data is wrong so maybe the scan tool is wrong. Someone could have used a different calibration from a different year vehicle. What is the three or four letter code on the chip? What's the ecm number? We keep talking about a 7747 but I can't find any verification.

  4. #19
    Electronic Ignition!
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    I hear what you are saying, it is a difficult situation . earth's are all good I have 5 of them , some direct to battery some to body, harness earth's are connected to these aswell. Both my ecm s are 7747 model , haven't taken Down chip code but it was the factory one from donor vehicle. CTS looks correct goes up as engine warms up. Map is wrong seems backwards , I have used vacuum pump on it but cannot get readings to look correct. That is reading through scan tool though so i should probably back probe it . Engine is running really smooth and seems to have good power. It's idle i'm not getting now. I am suspicious of the loom aswell but I have been through it wire by wire at ecm and plug end checking location , continuity , colour , pin location, signal v , earth's back to body. So I feel I have gone through it pretty well. As far as attaching resistors I'm not quite savy on what to do and what I'd be looking for. I will try get a vid up at some point so you can see.

  5. #20
    Electronic Ignition!
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    It appears I have fixed these issues and is running perfectly now!! Only thing I have to hook up still is vss as the loom goes straight from ECU to vss but I am unsure if they have the same signal or if I need a buffer to convert?

    To sum up mostly what I found a few days back ( i think I failed to mention ) I found the fuel regulator spring had rusted and snaped. (That was most likley causing the surge). Also two wires were reversed in my swap loom. I also fitted my other ECU as was worried it may have been damaged by wiring. Also I'm ignoring the scan tool info now as cannot be confident its correct. I also had a sticky IAC at the end of it all aswell.

    Thanks for everyone's input. Hope to get vss sorted soon and no further issues!!

  6. #21
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    Congratulations. There's nothing like luck to help persistence.

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