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Thread: Tbi ignition module failure

  1. #1
    Carb and Points!
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    Tbi ignition module failure

    Hi All
    I had a strange failure with a new ignition module yesterday
    it is running on a 1227747 with the stock coil
    I put heaps of heat paste on it but the car popped at high revs then a minute later stopped and would not restart.
    I checked the coil and initially thought it was that but fitted a new coil and it did not help.
    hooked a noid light up to the coil power and signal from the ignition module and I had no pulse.
    the strange thing is I still have injector pulse.
    I have disconnected the 4 wire plug that goes to the Ecm and still have no spark.
    I disconnected the tach and still no good.
    I am pretty sure the module is cooked but was concerned something else caused it but all the wiring checks out ok.
    is it possible a tacho could burn out the ignition module?
    The engine is a v8 and in a car that was originally a v6
    I am using the stock v6 tacho with a Dakota digital tach converter to change the pulses for the tacho.
    the dakota module part number is SGI-8 E.

  2. #2
    Fuel Injected! PlayingWithTBI's Avatar
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    What brand ICM do you have? There's a lot of folks that found cheap modules don't last long. I was just looking at reviews such as these, too many ICM failures on new equipment.
    https://www.summitracing.com/parts/s...ilter=1&page=2

    Try AC Delco, Delphi, or Davis Unified Ignition (DUI)
    https://www.summitracing.com/parts/ado-d1984a

  3. #3
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    Quote Originally Posted by Sheponaro View Post
    I checked the coil and initially thought it was that but fitted a new coil and it did not help.
    A defective coil could definitely damage an ignition module and as PlayingWithTBI pointed out, many of the new replacements are junk. It's unlikely that the tach caused the problem, but if the wire from the coil to the tach adapter shorted to 12v power, that would take out the module. Based on what you've said, it's more likely that the coil killed the original module and it's replacement.

  4. #4
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    Well, the module has circuitry that detects and conditions the signal from the pickup coil. One pulse per ignition firing. These pulses are fed as the reference to the ECM and the ECM uses these pulses as the basis for all the rpm calculations and injector firing.

    The module has more circuitry that will switch between using the conditioned pules or the ECM timing output and fire the coil. It is switched by the bypass signal from the ECM. The module will fire the coil at the fixed base timing until the ECU asserts the bypass and takes over timing duty. Then, the timing pulses come from the ECU on the EST wire.

    After this switch circuitry, the module has the actual coil driver that drives the coil.

    So, yes it's very possible the switch or coil driver part of the circuit has failed and the ECM can still get ignition pulses and fire the injectors.

  5. #5
    Carb and Points!
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    Thanks for the replies everyone, as I am in Australia the only ICM I could get locally was a Tridon brand that is most definitely cheap chinese. I have since ordered a coil and ICM from the over there it is all AC delco branded so hopefully better quality.

  6. #6
    Fuel Injected! 84Elky's Avatar
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    Maybe too late, but consider:

    IMO, one issue often overlooked is matching the coil with the ICM for high RPM performance. At high RPM, the ICM has to do 2 things:
    1. Provide maximum primary voltage to the coil so the coil can maximize secondary voltage to the plugs
    2. Ensure adequate dwell at higher RPMs, which is simply an increased ON time of the primary current to the coil to avoid coil saturation
    This is why there are high performance ICMs. Some may be good and some may be bad. That's why there's chocolate and vanilla ice cream. But if buying one, it's clear the manufacturer should be able to provide the above specs that make their product superior to the latest GM ICM (see below). And if not revving to 6500-7000 RPM, the latest GM ICM is likely adequate.

    A good article that explains the above. Although written in 2001, still applies today. It addresses large cap HEI distributors, but concepts same for small caps.
    http://www.superchevy.com/how-to/674...coils-modules/

    FWIW, here's some random ICM info collected over the years. Sorry, but attributions lost
    The ignition module is responsible for turning the ignition coil on and off and controlling the duration of current flow through the primary winding of the ignition coil. This allows the spark plugs to fire at a specific time according to the number of cylinders your vehicle has. It also controls dwell.

    ICM stamped '048' (GM 10402827): Retarded the timing advance beginning at 3,500 RPM permitting the use of 83 octane gasoline and the module acted as a speed governor. It seems like the OE Code 048 Ignition Control Module acted like a rev-limiter and limited the ignition advance above 4,000 RPM.

    ICM stamped '369' (AC Delco D1943A, GM 19179578): First used on the 1985-1993 Chevrolet Caprice with the 9C1 RPO Police option. This ICM does not retard timing starting at 3500 RPM, but provides 2 degrees additional advance from 4,000 to 5,000 RPM and a total of 6 degrees additional advance above 5000 RPM.

    GM replaced the "048" ICM with the "369" ICM. The replacement may not have "369" printed on it. The "048" was discontinued so GM felt like there was no need to differentiate between the two. If the AC Delco D1943A module does not have "369" printed on it, look for the GM part number 19179578 burned on the edge of the module. The 19179578 8-pin ICM was originally for the 9C1 Police Option in a Caprice. In 1989 GM made the AC Delco D1943A ICM (19179578) as the service replacement for all V6/V8 models through 1995. That was because the TBI swirl port (fast burn) cylinder heads needed faster and more total advance. Engines with aftermarket performance camshafts need faster and more total advance.

    HTH, Elky
    Last edited by 84Elky; 4 Days Ago at 03:15 AM. Reason: Updated incorrect link

  7. #7
    Fuel Injected! PlayingWithTBI's Avatar
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    Interesting. I remember reading a thread somewhere about different ICMs' latency (is that right?). What about the D1984A? Do you know how it's configured?

    BTW - that link you posted didn't work for me. "Looks like this content has rusted out",
    Last edited by PlayingWithTBI; 4 Days Ago at 01:04 AM. Reason: Wrong PN

  8. #8
    Fuel Injected! 84Elky's Avatar
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    Link has been corrected. Apologies. Do not know specs on D1948A, but if you get the latest GM/Delco version, your probably OK. Thought you were using 8-pin but now realize it's 7-pin.

    Here's some good info for ICMs in general:
    http://www.useasydocs.com/details/GM_7pinHEI.htm

  9. #9
    Fuel Injected! PlayingWithTBI's Avatar
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    Thanks for the links. We're using the 8 pin ICM on 87 - 95 TBI trucks but, as your link shows, the only difference is the G pin for ground.

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