Edmunds Answers

Answers

  • mrevil 09/27/11 8:57 am PST

    I remember that Sub., its been awhile. It was the weirdest thing. I replaced the ign. module and it still didn't run. I got frustrated with it and decided to make sure it was getting fuel up to the injectors. I cracked the lines and there was no fuel right off so I cranked it, the pump ran and after 10 - 20 sec. I had fuel all over. I re tightened the lines and it fired right up. I am assuming that the fuel was cavitating in the tank, it just needed to be bled. So I would try that first. If not solved, Then recheck the ign. module. Good luck with it. Dave

  • 94owner 09/28/11 12:26 pm PST

    Thanks for getting back to me - I did crack the fittings at the tbi, had fuel running out there...I guess to me, the issue is the fact I have no injector pulse. I need to know what else needs to be present for the ecm to fire them(ground). I'd hate to throw an ecm at it to have that not be the issue(like so many others have done!) - I'm going to check if the gm dealer can test it.

  • 94owner 09/29/11 3:15 pm PST

    Also, on two different days, I checked the ref v to the sensors, one day it was only .7 - now today when i checked it, the meter said 2.3! It is supposed to be 5 - could this be the ecm - I have two batteries in this one, both are newer and up to snuff...today, with this higher reading, with the key on, the fuel pump relay was clicking on and off - not rhythmically, more of a flutter - went back and the fuel pump was running(just with key on) not cranking...hmmm...I have checked the grounds on motor and ecm plugs, all are zero resistance to ground(solid) - I have batt voltage at orange wire(always), and batt voltage(key on) at pink and grey wires far right end of plug E-F....rev voltage for sensors(noted above) at the ecm always matches what I measure out on the motor...so, anyone think an ecm is the next thing? I'd appreciate any help. Thanks.

  • ace2483 09/29/11 10:53 pm PST

    I have a 95 2 door Tahoe
    with 5.7lt that is doing the same thing, I got 3 ECM's from the junk yard, 3
    fuel pressure regulators, got a map sensor and TPS from yard, new fuel
    pump, new ICM, new Dist. cap, fuel pump relay is working all fusses are good
    and it still will not work. So I would not get a new ECM just yet I got a
    friend that has a shop so he is giving me a helping hand and I am a mechanic in
    the army and have done this kind of work for 9 years now so I am hopping
    between us 2 we should have some kind of answer for you and I ether this week
    or next but if you happen to beat us to it please let me know. I think the next step I will do is take EVERY ground wire off the truck clean/sand the frame and clean/replace wire conector (re-wire what I can just the easy to get to grounds) and hook em back up, as the ECM does ground the injectors wich is what makes them pulse. I also have alldata so if you need any kind of info for this truck let me know and I can ether print it off, scan it or save it as a file not sure if that will work but can try and email to you just give me your email.



  • mrevil 10/02/11 4:08 pm PST

    The only thing that I can add to what you guys have already covered, is just to make sure there is ample fuel pressure. If you can put a gauge on it. The one I was working on wouldn't start until the pressure came up. It has been quite awhile since i worked on that thing but I do remember that the pressure was a issue. Good luck to the both of you.


    Dave

  • 94owner 10/02/11 11:56 pm PST

    Never mind - I figured it out...
    lol, that's what someone else did here, couldn't believe they didn't share the solution with the rest of us!
    First of all, CHECK ALL YOUR GROUNDS! I checked mine off the back of the ECM plugs while they were still plugged in, and they were all 0 resistance to ground(solid).
    OK, but here's what it was. On the ECM, there is an orange wire that is supposed to have 12v battery voltage all the time(key off). When I checked it(multiple times!) I had 12v there, so I thought it was good. What I didn't do, is check it while I turned the key on or was cranking(putting a load on that circuit). I'm sure most people would not check it while cranking because that is when you would be checking the OTHER terminals that are supposed to be getting voltage at crank! I don't know where it is, but there is a connector, or split in the circuit somewhere that is part of the fuel pump relay/oil pressure switch/ECM-B fuse supply(according to Haynes book schematic), and when I would turn the key on, the 12v supply(to the ECM only!) would drop to about 1v...now - key OFF, it would show 12v, but when it needed to, it couldn't supply any current! There is a bad connection somewhere that would basically go open when any current was needed - this is why I had flaky ref voltage to my sensors(it was different every day it seemed), I had no check engine light(self check when key is on), AND ALSO, no injector pulse! I'm thinking whatever grounds the injectors needs 12v to operate properly...now, even though I had only 1v to the ECM at that moment, there was still a solid 12v to the other devices on that circuit(fuel pump relay, oil pressure switch etc...the ONLY device on that circuit not getting a solid 12v was the ECM...I feel a little proud that I figured this out(a new ECM like so many have done wouldn't have made a bit of difference) - I hope this helps someone else out...I also found another possible future problem while changing my blower motor. You need to take off the pass side kick panel to loosen up the dash, and when I did, I found a bundle of wires and multiple connectors(all factory) that sit in a hole behind the kick panel, the largest connector has 8 wires that go to it...the GM engineers, IN THEIR INFINITE WISDOM, have this large connector sitting at the bottom of that hole on top of some of that factory foam filler crap that obviously gets nice and wet everytime it rains...or car wash, or you name it...the corrosion on my connector was incredible to me, because all the connections were still working! Needless to say, I cut the wires, soldered, and sealed them, along with wire tying them up off the bottom of this cavity...I'm done......again, I hope this book I just wrote helps someone out! lol-Troy

  • mrevil 10/03/11 11:03 pm PST

    Good job Troy, the Sub i worked on didn't have the corrosion problems of which you encountered. I would have remembered that for sure. The one i did work on did sit for 2 or 3 years before it ran. I didn't post what I did to fix the problem mainly because nobody tried to answer my question. It looks like we had totally different problems, Im glad you figured it out. Feels good doesn't it. Have a good one Dave

  • ironpuke 10/04/11 3:09 am PST

    there is no real way to test the ecu. ive seen of this with your vechile. it does sound like the ecm is bad. i would check the fuel regulator first

  • 94owner 10/04/11 3:32 am PST

    Thanks Dave - yes, it does feel good! The corrosion is a separate issue, I would really like to know where the connector thats failing on that circuit is...

    Iron, if you read up a couple, you'll see I solved it - it was not the ECM, but a flaky power wire that was the culprit.

    Thanks for the replies, guys.

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