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Discussion Starter · #1 ·
Hi guys,

my 95 Impala is giving me a hard time. Now, where do I start? Last year we took the engine out of the Impala to give it a BIG service. Replaced and maintenanced about everything you can do. Until a couple of weeks ago, it ran silk smooth, good acceleration, everything was as good as it gets in a 95 Impala with slightly over 100k mls.

Then, all of a sudden while cruising along, the engine just died. From one second to the other. And I was not able to start the LT1 again, it just would not fire. Checked fuses, connections, all did not help. After endless tries after about 45min later, all of a sudden it came back to life, as nothig has ever happened. Just to die again, 5min later. Next day I started it again, ran for a couple of minutes, then died.

So I began the search for the error. We need 3 things to start the engine: air, spark (at the right timing) and fuel.
Air: check
Fuel: check
Spark: fail (I held the ignition coil wire with the end usually connected to the opti-spark to the cylinder head, no spark whatsoever)

Last year, with the BIG maintenance, I already replaced the original opti-spark with the Accel opti-spark (not the best choice, I know). Also replaced the ignition coil and module with Standard-components. Now I bought a brand new ACDelco Ignition coil and module, did not help, still no ignition. Also bought a PCM and replaced that, no effect, no ignition.

Luckily I have a set of GM factory service manuals for my Impala and went through the diagrams. Conclusion: the ignition impulse reaches the ignition module, both high and lo reference signals from the opti-spark work like they should and reach the PCM.

So here I am running out of ideas - any suggestions?

Help is VERY appreciated (sorry for the long story)!

Thanks in advance :)
 

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Discussion Starter · #3 ·
Thanks Ron, I will look into it. Although I already checked most of the stuff listed.

Cheers, Florian
 

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Florian some things to try that you may have already done so, but it would be a good double check, when looking at the signals at the ICM and coil, did you check the ground with a meter, as well as did you ohm the wiring out to the PCM that controls this? Another thing to check make sure there is no corrosion on the opti spark connector at both the opti and where the pigtail attaches next to the passenger side fuel rail. The PCM also has an ignition control line that goes to the coil, was this checked? Do you have a spare PCM that you can throw in to check and see if it fires? Just some thoughts.
 

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Discussion Starter · #5 ·
Florian some things to try that you may have already done so, but it would be a good double check, when looking at the signals at the ICM and coil, did you check the ground with a meter, as well as did you ohm the wiring out to the PCM that controls this?
Yes, checked with a meter but I did not measure the wire for resistance.

Another thing to check make sure there is no corrosion on the opti spark connector at both the opti and where the pigtail attaches next to the passenger side fuel rail.
No corrosion there.

The PCM also has an ignition control line that goes to the coil, was this checked?
Yes, I did check that and the signal from the PCM to the ICM works like it should.

Do you have a spare PCM that you can throw in to check and see if it fires? Just some thoughts.
Yes, ordered one from SpareECM, makes no difference: http://cgi.ebay.com/ebaymotors/ws/e...20608216263&ssPageName=ADME:X:AAQ:MOTORS:1123

Thanks for the input! :)
 

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I am sure that you ran through this stuff, but some more information for you
CIRCUIT DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
The battery should be fully charged prior to any tests.

Check for proper output from the distributor ignition system. The spark tester requires a minimum of 25,000 volts to fire. This check can be used in case of an ignition miss, because the system may provide enough voltage to run the engine but not enough to fire a spark plug under heavy load.
This test will separate the distributor cap, rotor and ignition wires from the ignition coil to help identify a secondary ignition system problem.
This will determine if the proper available voltage exists in the primary ignition circuit.
This check will begin to determine if the Powertrain Control Module (PCM) is providing a signal to the ignition coil module or not. If the PCM is not providing a signal to the ignition coil module, the problem exists between the distributor and PCM.
A grounded coil circuit will cause the ignition fuse to open, and a no-start condition will occur.
DIAGNOSTIC AIDS
An ignition coil wire that is open or shorted to ground can cause a no start condition.
 

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Discussion Starter · #7 ·
Hi Mike,

yup, thats exactly the chart I was looking at, in my telephone-book-thick GM service manual. I can confirm that:
- the signal from the PCM to ICM (423 white) works
- ground to the ICM (451 blk/wht) is there, even measured resistance on that one, about near 0 from there to battery minus
- ignition fuse #5 (u/h), 10 amps is ok, but even replaced that with a new one
- ICM and coil are brand-new ACDelco
 

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Florian, even though you have checked most things, I would suggest that you start at the top of the article I posted and work your way through it. It won't take you long to do it and it just might identify the problem.

It has worked for me two times now (correctly identifying the problem). Once was a bad ICM and another time it was a bad coil.

Good luck to you.
 

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Discussion Starter · #10 ·
Once was a bad ICM and another time it was a bad coil.
.. which I already replaced both, actually twice now. First Standard Motor products, yesterday ACDelco.

But you are right, and thats exactly what I will do, to just start from square one and go systematically through it. Thats the only way to chase down these tricky errors.
 

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sounds like you have no fault codes and the primary system is working, have you tried swapping out the coil secondary wire?
could be failing inside, I dont remember the resistance specs for plug wire offhand.
 

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Discussion Starter · #12 · (Edited)
You mean the wire from the coil to the opti? Last time I swapped that was during the big maintenance last year. I actually ordered a new wire from ACDelco (just this single wire), but the shipped wire did not fit.

Oops, forgot to post that: yes, I have no DTCs.
 

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yes.
or carefully use a test piece of regular wire from coil to ground just to see if theres spark out of the coil.
 

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Discussion Starter · #14 ·
Good hint, never thought of the actual wire itself!

Strangely, the ACDelco Part# 340R did not fit. I ordered it at Rockauto and the wire that was delivered had the right length (or shortness) but the plug which should go to the opti was way too big, it was a plug for a spark plug...
 

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Discussion Starter · #15 ·
Eckoman, pretty good article that should help you:
http://www.mainstreamtopics.com/forums/index.php?showtopic=78
That hit the nail on the head!

The injectors were not triggered, worked my way through the guide and it pointed at a faulty opti. I just replaced the original ACDelco opti with an Accel unit a year ago, brand new! The original one did its job fine for 100k mls, I just replaced it as a precaution. So the Accel opti lasted for only about 8k mls - well, I read somewhere else that the Accel opti is not a good bet, proves to be right. Now I got a brand new ACDelco opti for $150 off eBay.

After throwing the new one it, the SS fired up the very first time we tried, as if nothing had happened. Yay!:)

Thank you guys!
 

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That hit the nail on the head!

The injectors were not triggered, worked my way through the guide and it pointed at a faulty opti. I just replaced the original ACDelco opti with an Accel unit a year ago, brand new! The original one did its job fine for 100k mls, I just replaced it as a precaution. So the Accel opti lasted for only about 8k mls - well, I read somewhere else that the Accel opti is not a good bet, proves to be right. Now I got a brand new ACDelco opti for $150 off eBay.

After throwing the new one it, the SS fired up the very first time we tried, as if nothing had happened. Yay!:)

Thank you guys!
just read through the entire post i was gonna say opti harness or opti...

:)

glad you figured it out.
 

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re: ignition wire set

[MODERATOR COMMENT: The following post is an example of spam. Please report all such posts. The admin will likely ban this member soon.]

hi buddy! need your help.
was trying to install a monitor in my car but ran into a problem. the ignition wire set that runs into the stock radios harness is no longer getting power. the constant 12v is fine, just the ignition/acc wire. where do these wires run to so that i could check the source and see if its disconnected or anything?
Any info would be greatly appreciated.
 
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