Question about 1999 Chevrolet S-10 Pickup

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I really need help with this car im completely stumped, ive got a 1999 holden VT commodore it has a new standard 3.6L V6 fitted, its been lowered proffesionally, has high flow extractors, a 2 and half inch full straight through exhaust system and also has a custom sound system, the problem is it has this nasty habit of randomly shutting down, the engine can shut off without warning or it can sputter a bit recover then sputter again and then shut off it appears to b completely random, i recently had my mechanic check it over and much to there surprise there computer wud not read my ECU they then found the alternator to b faulty as a result of a malfunctioning ABS relay i had both replaced with new parts this didnt fix the problem but did allow the computer to b able to read my ECU wich then gave over 400 error codes (obviously a false reading considering the engine couldnt b in better condition) they then cleared all the codes and waited for the current ones to reappear once the engine died again did that and got the error code immobiliser transponder signal weak which makes sense with the engine shutting off, got a new transponder tuned in but it didnt help at all car still shuts off and ECU stil says same error, its got me and the mechanics strumped, any help wud be greatly appreciated and please use detail and dont b afraid to use big words and technical infomation

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  • marley mcelhinney Aug 24, 2010

    yeah ok fair enough, wud i b able to get my mechanics to check compatibility? with the ECU earth wire r u saying to make my own earth from the ECU case? to test it, cud it b any earth wire in the car or is it most likely to b the engine or ECU earth? and wud and bad earth explain the bad ABS relay and alternator?

  • marley mcelhinney Aug 24, 2010

    ok fair enough, wud my mechanics b able to check compatibilty? so with the ECU earth r u saying to create my own earth to test it? cud it b any earth point in the car or is it most likely to b the engine or ECU earth? and does a bad earth point explain my bad ABS relay and alternator or wud that b unrelated?



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OK mate, see if we can get this sorted.....

When was the 3.6L V6 (I'm guessing an LY7) motor fitted to your VT and has it been running OK or has it always had this fault since being fitted?

400 codes from the ECU rings alarm bells that there is a compatibility problem with either the scantool and the ECU or the ECU and the engine.


I have struck issues in the past where all sorts of wierd things like you describe have been happening and it has been a poor earth to either the ECU or the engine block. (poor earths cause a LOT of problems and really random ones)

Transponder fault does not make alot of sense as it is only going to cause issues on startup, not once the engine is running.

I see the exhaust has been modified...are the factory Oxygen sensors for the 3.6L V6 fitted?

If you can give me some history of the repower ie: who did it, are the engine and ECU matched, where did the motor come from etc. It may give some more clues.



Posted on Aug 23, 2010

  • 4 more comments 
  • marley mcelhinney Aug 23, 2010

    i recently bough the car (obviously a bad decision) so i cant help much with history all i know is it is a long 3.6L V6 engine fitted by profesional mechanics i viewed reciept, my first suspect was a bad earth connection but didnt wanna **** round to much with it til afta the pro's took a look can u suggest an easy way of checking earth points? aside from getting the workshop manual and going over all of them, also how can i check the compatability of the ecu with the engine? and what is a scantool (sorry but car electrics isnt my strong point) do u hav an email address? it may b easier to talk that way

  • GeckoNZ Aug 23, 2010

    Checking earths can be tricky as you will only get voltage drop under load (when the circuit has current going through it). often easiest way is to run an earthed jumper lead to ECU casing to see if it makes a difference. But it could anywhere.

    Compatibility of ECU is going to be something only the dealer can tell you as the part numbers will need to be checked and matched up between the engine and ECU. They have all this info on their database.

    A scantool is an electronic device that allows a Tech to view information stored in the ECU and also live data. It is essential in diagnosing faults in the modern automobile.

    I am trying to gain expert status so communicating outside of the website will jeopardize my chances of getting paid later on. sorry.

    But happy to help as much as I can on here.



  • marley mcelhinney Aug 24, 2010

    ok fair enough, wud my mechanics b able to check compatibilty? so with the ECU earth r u saying to create my own earth to test it? cud it b any earth point in the car or is it most likely to b the engine or ECU earth? and does a bad earth point explain my bad ABS relay and alternator or wud that b unrelated? and how does the oxygen sensors on the exhaust affect anything?

  • GeckoNZ Aug 24, 2010

    I don't know of any way to check compatibility of an ECU to an engine other than through the manufacturer (Holden) and checking that the part numbers are ones that would have been in the exact same model car.
    In regards to earths, yes you can make up a little earth lead and run it from a known good earth point to the ECU. I would check a wiring diagram for the engine and check what colour to ECU earth is in the plug and backprobe that wire with the good earth wire.

    The whole ABS relay and faulty alternator thing sounds a little wierd, but without knowing exactly what was wrong with both I can't really comment any more than that. Like I said in my first post, bad earths can make all kinds of faults come up because the ECU gets craploads of signals that it just doesn't understand and logs codes for all of them. 400 error codes is what makes me suspect bad earth.

    If your mechanic has a scope (like a PICO or similar) and more importantly they know how to use it (alot don't) they should be able to get to the bottom of faults like this without too much problem.

    I asked about the O2 sensors as as you mentioned that the car sputters and then recovers sometimes. If the car is in closed loop then the O2 sensors aid the ECU with fuel trim and although unlikely can cause rough running, but only when the engine is up to normal operating temp.

    Forgot to ask, but I am guessing you are in Australia? or is it NZ?



  • marley mcelhinney Aug 25, 2010

    ok yeah my mechanics r jus pulling codes from the ECU and checking or replacing the part at fault wich isnt working cos the codes r obviously wrong as u said probably due to a bad earth, ive made a list of possible causes from info ive gathered from you and other sources and im going to get them to run diagnostics and tests on them things like a fuel pump flow test, blocked fuel filter, the ECU compatibility, EGR valve sticking, blocked up CAT converter and all earth points, relays, computers and wiring and now the o2 sensors (wont cost me much as they r mates and i will most likely help them do it) im from bunbury in australia

  • marley mcelhinney Sep 16, 2010

    ok ive ruled out a couple of things had the fuel pump tested works fine, had all relays and fuses checked all ok, had the majority of all sensors pulled and cleaned worked for a weekend with no issues then sunday nite engine clicked off with no warning with random dash lights showing up and it wouldnt start bak up jus cranked over with a few random pops from it trying to fire (engine light, oil light, airbag light, seatbelt light, ABS and traction control i think) the ABS and low traction light r fine there cos my ABS module blew so i unplugged it as it also caused my alternator to malfunction, but know the lights r gone and all works fine yet again im thinkin its gotta b the crank angle sensor cos it worked for a wile afta the mechanics cleaned it up



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