Opti? ICM? Coil? Now what? - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
 
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post #1 of 12 (permalink) Old 07-30-2019, 11:27 AM Thread Starter
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Unhappy Opti? ICM? Coil? Now what?

I have a 97 Trans Am with a LT1. I changed the OPTI spark because it wouldn't start a week later the coil was over heating so I replaced that. Ran great for 2 weeks then on my way home while driving it stalled out, i put it in neutral and it started right up (only had been driving for about 5-10 minutes when it stalled out) next day drove to gas station (5 minutes away) went to start it wouldn't start just turns over. waited 15-20 minutes and it started. After work I let it run in the garage for an hour no issue. I had been running it in the garage for a week, even took it on a trip around the block, ran great. Went to the store and on the way back died. Next day fired right back up and have had it idling in the garage for hours at a time. Yesterday while idling it finally stalled. Checked and no spark. I am going to start with the ICM and go from there but at least I can rule out the fuel pump now.

Last year I replaced the fuel pump, ICM, CPS, Fuel Filter, Fuel relay and origionally coil (in March of this year)

I have noticed that when idling the oil pressure gauge sometimes works, and sometimes doesn't?? I don't know if this has any connection to anything. I have never read anything with the oil pressure being connected to no spark.
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post #2 of 12 (permalink) Old 07-30-2019, 11:56 AM
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Have you tried downloading the 96 service manual at the following link. It has code explanations & troubleshooting. It is essential that you scan for codes. The icm & opti codes don't light the ses. My Files


When you change an icm you need to put heatsink compound on it's back and on metal sink. Same stuff used on computer cpu. Without the heatsink compound, the icm will fail.
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post #3 of 12 (permalink) Old 07-30-2019, 12:29 PM Thread Starter
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Have you tried downloading the 96 service manual at the following link. It has code explanations & troubleshooting. It is essential that you scan for codes. The icm & opti codes don't light the ses. My Files


When you change an icm you need to put heatsink compound on it's back and on metal sink. Same stuff used on computer cpu. Without the heatsink compound, the icm will fail.
Thanks for the reply.

I have a code reader that I bought off Amazon ($100) and I never get any codes.

I am going to start with changing out the ICM with the other one I have. I need to wait until the car fails to start again as it starts (every time I try to work on it!!). I am not sure if it is the ICM though as the car isn't really "hot" when it stalls. Plus I have moved the coil and ICM away from the block to get air circulation around it.
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post #4 of 12 (permalink) Old 07-30-2019, 03:27 PM
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Get a fuel pressure tester and hook it to fuel rail. Key on prime should be around 43 psi. With engine idling pressure should be mid 30's psi. And at least 40 psi for other running conditions.

Tape gauge to windshield. See if fuel pressure drops right before engine stalls. Have you installed a new fuel filter? It needs to be changed about every 30K miles. Also there is a filter sock on the fuel pump pick up tube. It can get mostly blocked. And this can cause intermittent stalling. As well as clogged regular filter.

Does your security light come on, then cycle off when you turn key on? This is normal operation for security system. If light stays on or comes on when your driving, car can stall do to security system cutting fuel injector operation.

You need to buy a PC based oscilloscope. This is only 100% way of testing low & high resolution opti signals. Funny thing about opti codes is; if both low & high res signals fail intermittently, or all the time, no code will set. So test low & high res signals with scope. When engine stalls, see if low or high res signals either drop out completely, or change wave form from it's normal square wave.

PC based oscilloscope is around $70 on Ebay, Amazon, etc.

Last edited by cocobolo95; 07-30-2019 at 03:31 PM.
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post #5 of 12 (permalink) Old 07-31-2019, 09:51 AM Thread Starter
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Originally Posted by cocobolo95 View Post
Get a fuel pressure tester and hook it to fuel rail. Key on prime should be around 43 psi. With engine idling pressure should be mid 30's psi. And at least 40 psi for other running conditions.

Tape gauge to windshield. See if fuel pressure drops right before engine stalls. Have you installed a new fuel filter? It needs to be changed about every 30K miles. Also there is a filter sock on the fuel pump pick up tube. It can get mostly blocked. And this can cause intermittent stalling. As well as clogged regular filter.

Does your security light come on, then cycle off when you turn key on? This is normal operation for security system. If light stays on or comes on when your driving, car can stall do to security system cutting fuel injector operation.

You need to buy a PC based oscilloscope. This is only 100% way of testing low & high resolution opti signals. Funny thing about opti codes is; if both low & high res signals fail intermittently, or all the time, no code will set. So test low & high res signals with scope. When engine stalls, see if low or high res signals either drop out completely, or change wave form from it's normal square wave.

PC based oscilloscope is around $70 on Ebay, Amazon, etc.
Thanks for the reply!
I will look into the oscilloscope, some really good information there.
As far as the fuel pressure goes, the car has no spark, I have a spark plug tester hooked up and if it does start it has nice spark but when it turns over no spark, so I am not even looking at the fuel system.
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post #6 of 12 (permalink) Old 08-02-2019, 07:27 AM
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Follow the troubleshooting info in the 96 manual for a no spark & a no start condition. They will give you step by step instructions on testing.

Once you get the PC based scope, test the low & high resolution signals your opti is sending to pcm. They should be square waves with no changes to waveform, or drop outs where waveform disappears.
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post #7 of 12 (permalink) Old 08-02-2019, 12:19 PM Thread Starter
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Thank you!
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post #8 of 12 (permalink) Old 09-07-2019, 02:33 PM Thread Starter
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Ok on my 3rd opti this summer, the latest I put in I took the old sensor from my original opti and this time it won't even get spark.

I have talked to may people and have been given some advise, some believe that I am wasting my time changing out the opti's and being the third one I've been told that it isn't my issue. But after changing ever one out the car fires and runs. The first was a month the second only a day. This one no spark, but I did changed the sensor. The bearing in my original opti looked bad and the disc was spinning lop sided so there is aa chance that it ruined the sensor, but I took that risk.If it isn't the opti going bad then why would the car fire up after I change them.

So I did the tests and here is my results. Note the battery in the car isn't the strongest (because of all my trying to start it).
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground.*Note:*Use a modern digital meter with at least 10 megohm impedance to protect the PCM (in case you measure anything in that direction). Do not use a test light for looking at voltage potentials from electronics! Also make sure your meter leads make good contact and are clean and tight. Check that you get a zero ohms reading by touching the two leads together. If it is not zero, merely adjust the readings you take by the skew. That will ensure accurate resistance readings. On "A' i had a reading of over 10 volts and on "D" I was around 4-5 volts.
*Result should be 10v dc or more on the A and D terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to*ac scale*and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).On "B" while cranking the engine I was getting between 2-4 volts.
I might be missing ssomething, but I didn't really understand "to Ground" I had the negative of the multi meter grounded out on the car. My buddy thought that "C" might have been ground, but looking at the wiring diagram that looked like it was power, but the instructions from shoebox only said to*You should also check "C" of the ICM harness for continuity to ground.I put the volt meter on the "C" and the negative to ground on the car and had continuity that way.*

So I am not 100% positive if I followed these instructions correctly or not. I am challenged on multi meters but am trying to learn. I find it easier to change the opti out than read a meter. LOL
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post #9 of 12 (permalink) Old 09-07-2019, 06:15 PM
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Time to grab the bull by the horns. Buy that $70 PC based oscilloscope. Learn how to use it. Then any time you suspect opti, see if low & high resolution signals from opti are the proper square wave. This is only 100% way to test opti signals.

On no start conditions, you can also use scope to test 50 hertz fuel enable signal that bcm sends to pcm. You will find fuel enable signal at pcm connector A, cavity 25.
It's a dark blue wire.
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post #10 of 12 (permalink) Old 09-09-2019, 10:23 AM Thread Starter
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Quote:
Originally Posted by cocobolo95 View Post
Time to grab the bull by the horns. Buy that $70 PC based oscilloscope. Learn how to use it. Then any time you suspect opti, see if low & high resolution signals from opti are the proper square wave. This is only 100% way to test opti signals.

On no start conditions, you can also use scope to test 50 hertz fuel enable signal that bcm sends to pcm. You will find fuel enable signal at pcm connector A, cavity 25.
It's a dark blue wire.
Like this one?
https://www.ebay.ca/itm/New-2-4-LCD-Display-DSO150-Digital-Oscilloscope-Assembled-With-Case-Test-Clip/222948398748?hash=item33e8c2969c:g:2BwAAOSw32lctsP q
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post #11 of 12 (permalink) Old 09-09-2019, 06:39 PM
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Yes, this scope has enough bandwidth to measure opti & fuel enable signal. The unknown factors are weather or not scope will work at all. And if it works, how long it will last.

My $70 PC based Hantek 6022BE scope is 5 years old and still works flawlessly. There are several advantages to the Hantek. 1st it's a dual channel scope. You can test both low & high resolution signal at once. 2nd, PC laptop screen is much bigger than 2.4 inch screen of model you linked to.

If you.ve never used a scope before, it will take a while to learn adjustment necessary to bring signal being measured into view on the scope. So get as much practice as you can, playing with controls.

Last edited by cocobolo95; 09-09-2019 at 06:45 PM.
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post #12 of 12 (permalink) Old 09-16-2019, 12:44 PM Thread Starter
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I believe that I found the issue, the connector that goes to the coil (green wire) seems like it is not getting the connection it needs. My original testing that I did, I think I was wrong. After hours and help I think I am on the right track
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