Ignition module failing?
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HT4100 4.1, 4.5, 4.9 Discussion, Ignition module failing? in Cadillac Engine Technical Discussion; I've been chasing a misfire at idle in my '93 Eldo 4.9 for some time. It is progressively worse as ...
  1. #1
    DFBonnett is offline Cadillac Owners Fanatic
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    Question Ignition module failing?

    I've been chasing a misfire at idle in my '93 Eldo 4.9 for some time. It is progressively worse as the engine reaches higher operating temperatures such as in traffic in warm weather. It is also progressively more noticeable as more load is put on the engine such as putting it in gear or turning on the A/C. Plugs, wires, cap rotor, coil, injectors, FPR, pump pressure, etc., all check out OK. Those parts have all been replaced or tested according to the FSM. No codes. No discernible vacuum leaks.
    Can an ignition module begin to fail slowly producing these kind of symptoms prior to complete failure? I know they can have intermittent failure due to heat and produce a no start condition. I'm out of ideas and would rather not wait for a precipitous failure to fix this. Any guidance would be most appreciated.

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    Doc203 is offline Cadillac Owners Member
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    Re: Ignition module failing?

    My 1st thought on a symptom such as your describing is plug wires OR injectors. Both will give you the same effect and both are more likely to fail under heat. I have never had a GM HEI ignition module do that. They will usually as you said cause a no start condition. I am not saying that it is impossible, I just have never seen one cause that.

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    Doc203 is offline Cadillac Owners Member
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    Re: Ignition module failing?

    One other thing... if this is only at an idle as I just re-read your post and figured out then the above statement is only partially true. The module most likely is still not it... I would look hard for a vacuum leak or an IAC valve that is plugged with crud or malfunctioning etc. Sorry for mis-reading your post.

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    DFBonnett is offline Cadillac Owners Fanatic
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    Re: Ignition module failing?

    Thanks for the suggestions. I can't locate any vacuum leak using the usual tests. The 4.9 doesn't have an IAC to test. I'll just keep digging.
    I'm kind of a funny guy. Unless I know that a car will be 100%, I don't want it. I'll put some more time and money into this one but at some point I'll just dump it and buy a new Lexus and have done with it. I hate to shitcan a car with only 58K on the clock but if it's going to be unreliable, then that is my only option.

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    92Presidential is offline Cadillac Owners Member
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    Re: Ignition module failing?

    my car was doing the same exact thing...its the Hall Effect Switch...often referred to as a Cam Sensor...its under the dist. cap...I'm almost certain its that

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    DFBonnett is offline Cadillac Owners Fanatic
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    Re: Ignition module failing?

    Quote Originally Posted by 92Presidential
    my car was doing the same exact thing...its the Hall Effect Switch...often referred to as a Cam Sensor...its under the dist. cap...I'm almost certain its that
    Thanks for the heads up on th cam position sensor. How did you determine that was your problem?

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    Re: Ignition module failing?

    when you get a miss like that, and you may think it is coming from the dist. area, you may want to check the wiring harness terminal block to make sure it is not damaged. if you feel you are getting no spark, hook a timing light up to EACH plug wire to confirm this. the other thing you can do is enter the diagnostic mode and try to disable each injector. you can do this by following the instructions regarding engine codes at the beginning of this forum. just find the "ecm override" and find the injector disable. disable each one to isolate the problem.

    good luck

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    92Presidential is offline Cadillac Owners Member
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    Re: Ignition module failing?

    my car ran like it was running out of gas...missfiring all the way...it would get worse as the car warmed up and when applying any sort of acceleration to it. I took my car in to my mechanic...I'd only had the car since early summer...I let him go through the engine. my car has 160K on it and apparently the wires plugs and filters had never been changed. my mechanic changed the Ignition Module Dist cap...wired plugs...dist roter...and recommended changing the coil. my car was tossing a code think is was something like E0-41...whatever the code was it was the code of a malfunctioning Cam Sensor...so I had it changed...and boom good as new...runs great now...

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    DFBonnett is offline Cadillac Owners Fanatic
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    Re: Ignition module failing?

    Well, it wasn't the ignition module causing the poor idle. Somehow I buggered up the original module while poking around inside the distributor and had a dead car blocking my whole driveway. Took an educated guess that the module had died and replaced it. Started right up but the idle problem continues.
    There were/are small bits of plastic from deteriorated connectors down in the distributor. I vacuumed then blew out as much as possible with compressed air and will replace the 6 terminal 5 wire connector ASAP.
    At this point I think I'll have to just wait for it to get bad enough to throw a code then go from there.

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    Re: Ignition module failing?

    Quote Originally Posted by DFBonnett View Post
    I've been chasing a misfire at idle in my '93 Eldo 4.9 for some time. It is progressively worse as the engine reaches higher operating temperatures such as in traffic in warm weather. It is also progressively more noticeable as more load is put on the engine such as putting it in gear or turning on the A/C. Plugs, wires, cap rotor, coil, injectors, FPR, pump pressure, etc., all check out OK. Those parts have all been replaced or tested according to the FSM. No codes. No discernible vacuum leaks.
    Can an ignition module begin to fail slowly producing these kind of symptoms prior to complete failure? I know they can have intermittent failure due to heat and produce a no start condition. I'm out of ideas and would rather not wait for a precipitous failure to fix this. Any guidance would be most appreciated.
    Old thread... Anyway, I have been lately experiencing exactly the same symptoms. Replaced all injectors, but the idle is still rough and get worse when engine is hot. No codes. Probably it makes sense to replace the distributor instead of playing with its components. What do you think, gents?

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    DFBonnett is offline Cadillac Owners Fanatic
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    Re: Ignition module failing?

    Quote Originally Posted by HUF View Post
    Old thread... Anyway, I have been lately experiencing exactly the same symptoms. Replaced all injectors, but the idle is still rough and get worse when engine is hot. No codes. Probably it makes sense to replace the distributor instead of playing with its components. What do you think, gents?
    Did that, but piece by piece. Still no joy. I don't think the problem is the distributor. EGR, MAP sensor, vac lines, FPR, fuel pressure, TPS, O2 sensors, all pass diagnostics in the FSM. I'll be following your progress carefully as it BTSOOM.

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    Re: Ignition module failing?

    Quote Originally Posted by HUF View Post
    Old thread... Anyway, I have been lately experiencing exactly the same symptoms. Replaced all injectors, but the idle is still rough and get worse when engine is hot. No codes. Probably it makes sense to replace the distributor instead of playing with its components. What do you think, gents?
    I had a problem with constant stalling and rough running with my car some time ago, even after replacing the fuel injectors. Once I changed out the ignition control module, the problem was solved. I think it was just a $30 part and easy to change out, so might be worth trying before investing in a new distributor.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Ignition module failing?

    If it's really heat related it may be the coil. Coils are pretty cheap. This guy from 04 fixed it with a hall effect sensor.

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    SubieHo is offline Cadillac Owners Member
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    Re: Ignition module failing?

    I've experienced this with different vehicles. It's true that coils can show problems only at operating temperature, but this would usually produce a no start condition. Could try testing it when it's hot.

    I'm new to GM, but it sounds like an engine management issue and not a problem with ignition components, especially as the original poster had replaced all those parts.

    Without a trouble code, though, it's hard to know where to begin. Symptoms sound like the engine is running in open loop, which could be the coolant temperature sensor or a host of other sensors that determine fuel delivery and ignition timing.

    Again though, it's strange that it wouldn't throw a code.

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    Re: Ignition module failing?

    Thanks for the suggestions, gents. I'll be back to this subject if/when I make some progress.

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