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  1. #1
    LTX Master


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    Default Car shutoff, possible ICM, looking to find out

    Been a long time since the Z has given me any real problems. After driving a couple hours in the heat it shutoff on me. Started back up for 2 seconds, then wouldn't crank at all. Accessories still worked. Let it cool down and it started back up and drove it about 5 minutes home. First thought was opti, but after some research its sounding more like an ICM or coil issue. All my ignition parts were replaced about 10 years ago so they have had a good run. Scanner didnt pick up any codes after it cooled down. So I'm looking for other possible ideas or how to diagnose the ICM without running around and getting stranded again so I can pick up a code lol. Thinking about just replacing it and the coil as a precaution anyways but want to rule out other suspects if there are any.
    Thanks for any input fellas
    MATT

    95 Z28 - Forged 383 LT1, Performabuilt Stage 2 4L60E w/3200 stall, Pacesetter LT's & ORY with a stockish exhaust (E-cutout soon to come!)

  2. #2
    LTx Guru


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    Default

    Have the ICM tested at an auto parts store. Just make sure they get it good and hot. Surprised no codes for the ICM. If it shut the engine down, would expect a "stored" code.

    Test coil continuity:

    http://shbox.com/1/coil_testing.jpg
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  3. #3
    LTX Master


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    No code suprised me too. I guess when it was working again wasn't throwing one. The check gauges light came on when it shut off but I didn't have my scanner on me.

  4. #4
    LTX Master


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    Default

    Just saw your link as well thank you. Is this the same test an auto parts store will perform? If so, I have the capabiltity to do that myself. For the ICM is it tested on the car while hot, or does it need to removed and heated artificially?

  5. #5
    Long Live the Opti


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    No cranking wouldn't be the ICM. It'll still crank over with a bad ICM, just won't fire off.
    Quote Originally Posted by Ryan Stout View Post
    I would try to work my neck muscles but I'm not invited to the LS guy parties.

  6. #6
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    As far as the codes go, if a codes is set, it is "stored" and should show up in a scan, even if the problem is no longer "active". At least if you scan it shortly after the light first went on, and haven't cleared it by pulling 12V power from the PCM. Problem doesn't have to be active to pull a code. The code will clear itself, after quite a few drive cycles without the problem recurring.

    After doing this for almost 20 years, problem is different people use the term "crank" in different ways... some use it to describe the starter actually cranking the engine, others use is to describe the engine actually trying to start. Gets confusing, but see it all the time. Same with "turn over". Generally, before I respond, I ask for a clarification, but in this case I didn't - my fault if I interpreted it incorrectly.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  7. #7
    LTX Master


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    To clarify: it shut off, started back up for seconds, then clicked a few times as if the starter or battery was going out, then just a simple click to nothing. But accesssories worked during this time. I should have been more specific, I know people have different ideas on clicking, cranking, turning over etc.

    I didn't think heat soak would be an issue with the starter but I could certainly be wrong. I am just hoping the opti is not to blame.

  8. #8
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    My mistake. A problem w/ the ICM, coil, or the Opti is not going to prevent it from engaging the starter. Heat soak can be an issue with the starter. And they can develop dead spots in the windings that will cause the starter not to respond, although it may "jiggle" the windings enough so it will eventually start after repeated tries. My 94 had the starter replaced by the dealer under warranty with less than 30,000 miles for exactly that reason.

    At the age of these cars, the ignition switch is starting to show up as a problem more frequently now. The body of the switch melts, and the contacts get burned. Would explain absence of codes on shutdown and failure to restart immediately. See first paragraph of this article from Shoebox:

    http://shbox.com/ignsw/ign_switch_repl.html
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  9. #9
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    Hmm ignitin switch didn't cross my mind but would be a welcome alternative to the opti. I can't remember but it's possible I had the switch replaced somewhere around 12 or 13 years ago when I first bought the car and it died. Probably didn't keep the receipt back then like I do nowadays. I really appreciate all this info, anything I can do to keep it out of the shop is what I'm looking for.

  10. #10
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    I havent had a chance to go out and test anything yet but I remembered a piece of info that may or may not help narrow it. For the past couple years, I have gone through batteries a few times. I thought I had a possible draw somewhere til the last battery I bought seemed to stay good for a while even not being started frequently. It got to the point especially in colder temps that I required a jump just to start my car and let it run for a while every couple days. It occassinally happened overnight even. I attributed this to the cold though. This last battery was holding very well even letting the car sit up to 2 weeks without starting it would fire right up. Then randomly it wouldn't crank, turn over or attempt to start at all. I jumped it and kept it going up until it shut down driving. I'm wondering if it's related.
    On a side note, I looked at coils, ICM, ignition switch from ACdelco and after seeing the prices, I think I will dumb down to being a "parts swapper" on them. I'll still test them afterwards but for the price and doing the work myself, I see it as insurance for the future. 10+ years on all these parts with the heat issues I've read about is enough to make me comfortable replacing them as a precaution... hopefully I don't get crap parts from ACdelco.

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