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LT1 Corvette - no spark FML!


zeitgeist57

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Well, fuck this shit. :(

 

I bought a new Opti from Dave at O'Reillys. Put it in and got it buttoned up. Started it tonight and it revved to life well...settled into a smooth idle and I was really hopeful. Drove it down my street - not goosing the throttle or anything - and it was running as smoothly as it ever had. I get to a stoplight and "BLOMP! BRAAAB-BRAAAB-BRAAAB..."

 

CEL comes on and the engine starts loping again at idle like the computer pulled timing. Same. fucking. symptoms. :( :( :(

 

Pull the codes when I got home: H41, H42 and now H72.

 

I'm guessing it's the ICM or the ECM...both computerized and expensive parts.

 

I could type a 20-paragraph about how pissed I am about it not being the Opti, but what would it do me or anyone else? In all seriousness, I am feeling very emotionally drained after that drive. I really thought the Opti would be the fix all along, after living with this problem for the last couple of years. Very sad indeed. :(

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Damn man, I had my fingers crossed that would solve all the problems.

 

Rick, thanks for storing my ECM on your laptop on Saturday. If I get a new PCM can we just plug in your laptop to my 'Vette's ALDL to "reflash" it?

 

That's definitely my angle of attack right now.

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Rick, thanks for storing my ECM on your laptop on Saturday. If I get a new PCM can we just plug in your laptop to my 'Vette's ALDL to "reflash" it?

 

That's definitely my angle of attack right now.

 

As far as I know we can do exactly that. I did some quick looking to see what error code 72 was.

 

41 Ignition Control (IC) circuit (open circuit)

42 Ignition Control (IC) circuit (shorted or grounded circuit)

72 Vehicle Speed Sensor loss (automatic transmission only)

 

Why you would get a code for an automatic transmission is beyond me.

 

My assumption is the PCM in the Corvettes is the same as the PCM in the f-bodys. I can't think of any reason they would be difference because it is the same drivetrain. I shot a quick email to PCMforless, maybe they can fill us in on the differences between the Vette PCMs and the f-body PCMs.

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I found out that - according to several sources - Blue Streak Electronics is the place to go for ECM/PCM rebuilds. Problem is, you need to have a corporate account to use them. No problem, as my good ol' http://www.rockauto.com carries a 3-5 business day rebuild with them for only $92. I'm going that route and hopefully Blue Streak will fix whatever is ailing my ignition system.

 

The other issues could be Spark Module (chip that inserts in ECM), or the ICM.

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Rick, thanks for storing my ECM on your laptop on Saturday. If I get a new PCM can we just plug in your laptop to my 'Vette's ALDL to "reflash" it?

 

That's definitely my angle of attack right now.

 

This is straight off of GM Service Info

 

Ignition Control Not Operating Properly (LT1)

Diagnosis

An open IC circuit will set a DTC 41. Refer to DTC 41. A grounded IC circuit will set a DTC 42. Refer to DTC 42. An open or grounded IC circuit will result in a no crank condition. Refer to No Crank .

 

An open or ground in the low resolution signal circuit will set a DTC 16 and the engine will not start. Refer to DTC 16. If the high resolution signal circuit becomes open or grounded, a DTC 36 would set. Refer to DTC 36. This will cause reduced performance and poor fuel economy.

 

The PCM uses information generated by the following sources in order to calculate spark advance:

 

The MAP sensor

The ECT sensor

The engine RPM

The PCM determines that more spark advance is required when the following conditions exist:

 

A cold engine

A minimum load, based on engine RPM and low air flow

The PCM determines that less spark advance is required when the following conditions exist:

 

A hot engine

A heavy load, based on engine RPM and high air flow

 

Problem is this stuff is so outdated it's incomplete, but it would be nice to check the function of your ECT and MAP sensors.

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Don't know if this will help but here you go, from alldata.

 

edit: looks like the url has changed

 

Shoot me a PM if you want to discuss a little more, I wish I'd have looked at this sooner. My doubts are on the PCM as that isn't usually the cause on many cars.

Edited by Cordell
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That was one of the reasons I removed the Del-teq ignition system from my car. I just don't understand it enough to troubleshoot problems. Also, the codes being thrown may or may not have anything to do with the problem because of the Del-teq. Clay, was there an ICM board you could try in that box of Del-teq stuff I gave you?

 

I know this would be a pain in the ass, but what about switching temporarily back to a stock style ignition until you track down the problem? With the Del-teq out of the system the problem may either go away, or become more visible. Anyone have any spare LT1 ignition components laying around we could use to troubleshoot with?

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Rick, Dave suggested it might be the ICM board (Caddy Northstar-style) in your bag. If DelTeq used a cheap aftermarket that might be the case...Dave suggested finding a scrapped Caddy and yanking the ICM board, but you know I don't have time to do that...

 

At this point, I have a brand new Opti (with good cap and rotor) so I would be happy to revert back to a stock-style system. Am I missing any wiring harnesses at this point?

 

I'll hit up a couple of people to see if I can borrow a stock coil/ICM...

 

FYI: cancelled my order to rebuild my PCM from Rockauto for now...getting a full refund.

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Other than a coil and ICM, you'll need a set of wires that fit. The ones for the del-teq are all the wrong length. I suppose I could bring the Camaro over and we could pull my coil and ICM for a quick try, that should not be bad.

 

I snagged a set of wires for the Impala from jegs last year and they were a decent price ~ $40, maybe our guys over at Oriely have a better hook up. I put over the valve cover wires on the Camaro and I like them a lot.

Edited by Richard Cranium
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Alright, I ended up buying a new/reman BWD (Borg Warner) ignition control module for a Caddy Northstar at O'Reillys. Put it in tonight...no improvement. :( After the engine warmed up a bit, the same H41, H42 codes came on and the engine dropped timing...climbing the rev band like it was missing a couple of cylinders but still with a smooth idle.

 

I'm still thinking it could be the PCM, only because the A/C compressor doesn't turn on now when I activate the climate control??? PCM screwy?

 

I have a good Opti, but I either need to go back to a stock setup with LT1 ignition components, or go rebuild of PCM from Blue Streak and see if that helps...

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o well i was going to say i have a 92 vette sitting in the garage but you are a little far away to swap a pcm for test

 

Needs to be a 94 or 95 PCM anyhow. Only those years will do. I did find out though that the PCM from the F-body is the same, only has a different part number. Got that straight from PCMforLess.

 

I might be able to pull the PCM from the Camaro next week and we could try it. I just have to remember to download the current tune. I have the mail order one, but not the newer dyno tune that Brian did for me.

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Why can't the stock Camaro tune work? Does the PCM talk to other parts of the car? I was thinking that as long as the PCM had a program it should work...

 

Actually the stock tune might work, unfortunately the current tune is not even close to stock. Between the larger throttle body, higher flowing injectors, cam, exhaust, etc... I doubt the vette would even fire up.

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