LT1-LT4 Modifications 1993-97 Gen II Small Block V8

Rough idle=optispark?

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Old 02-23-2011, 07:33 PM
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Ok now call me stupid but i tried looking for the schrader valve on the back of the intake and i dont see it. Does anyone have a pic of where exactly its at? Also, i got a better look at the opti and its covered with gunked up oil on the top of it. I will try again tomorrow to look for the valve. Im still thinking it could be the opti though. When i did have it started for a few seconds a couple of days ago, it just felt and sounded like it wasnt running on all cylinders. I mean i gave it a little bit of gas just over 1000rpm and it pops. Then the cel comes on but it wont give me any codes. Im not ruling out fuel yet either.
Old 02-23-2011, 07:49 PM
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ok i just found a pic on shbox's website of where the schrader valve is. I will try again tomorrow. Does anyone else still think it could be the opti?
Old 02-24-2011, 05:22 PM
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Ok I just did the fuel pressure test. When I turned the key I got 42psi. Over the course of 25mins it only dropped 2psi and it held there. When I started it, at idle it was 42. When I tried to rev it up a little it climbed up a few psi. So im thinking its not the pump. Also, I could smell alot of gas coming out of the exhaust. Im starting to really think it is the opti. Anything else I can try before I order a opti? Thanks for everyones help so far. Mike
Old 02-24-2011, 05:33 PM
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Did you ever check the coil ? there cheap and easy to put on. Symptoms sound like what happen to me once when thee coil was bad. Or a burnt plug wire, sorry I tried to read as much as I could
Old 02-24-2011, 05:55 PM
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Yes I had the coil tested. They did the test 3 times and it came back working fine each time.
Old 02-24-2011, 08:28 PM
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OK....the car is running great now. After i checked the fuel pressure, i went and put a new battery in because it seemed like it wasnt holding or taking a charge. Then i went to eat for an hour and came back to try and scan the codes again. Well i started it up and its running great now. Could it have really just been the battery?? Im dumbfounded as to why it was the battery. I gave it a couple revs and no more popping.
Old 02-25-2011, 10:22 PM
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anybody have a clue as to why it was the battery causing my symptoms? Im glad its running good now just wondering why the battery could have caused all my headache. Thanks to all that helped. Mike
Old 02-26-2011, 01:11 PM
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You never know. Maybe you had a bad connection, poor ground, something related to that. It may not have been the battery itself causing the issue, it may have.
There are several different ways a battery can fail internally. Your battery could have been in a condition of not holding a charge, and "refusing" charge from your alternator, causing the entire electrical system to be compromised.
Old 03-01-2011, 08:57 PM
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OK, problem is back. The car was fine for a few days. I go take it on a decent drive today and the same problems came back. It will barely hold a idle, lots of popping if i try and give it any gas, i also smell alot of fuel coming from the exhaust. I am really leaning towards the opti now. The cel is on but i cant read the code with any scanners so i have the cable on order so i can check the code first. Anything else it could be? I already had the battery, icm, and fuel pressure checked before and they are fine.
Old 03-09-2011, 11:32 PM
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Originally Posted by 95chevyz28
OK, problem is back. The car was fine for a few days. I go take it on a decent drive today and the same problems came back. It will barely hold a idle, lots of popping if i try and give it any gas, i also smell alot of fuel coming from the exhaust. I am really leaning towards the opti now. The cel is on but i cant read the code with any scanners so i have the cable on order so i can check the code first. Anything else it could be? I already had the battery, icm, and fuel pressure checked before and they are fine.
IDK But you think it might be your alternator? driving with a fresh battery and running good but alternator may not be charging, your battery may have worn down and not have enough juice to fire the ignition. just a thought
Old 03-10-2011, 08:44 AM
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Have you checked to make sure that all of the grounds are clean and tight?
for some reason people like to neglect the ground strap between the driver's side head and the framerail.

Originally Posted by 93z in hawaii
IDK But you think it might be your alternator? driving with a fresh battery and running good but alternator may not be charging, your battery may have worn down and not have enough juice to fire the ignition. just a thought
That too. If you can charge the batter up and start it without issue, but the problem comes back over time ... it might very well be the alt.
Old 03-10-2011, 10:20 AM
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well see this is what is wierd. The car starts perfectly fine, everytime. Meaning the battery is taking a charge and holding it. I definetely know the last battery was bad. Im still waiting to take a look at the grounds. If for some reason i dont see the ground from the driver side head to framerail, can i make another one?
Old 03-10-2011, 10:37 AM
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keep us posted please!
Old 03-10-2011, 10:38 AM
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Originally Posted by 95chevyz28
well see this is what is wierd. The car starts perfectly fine, everytime. Meaning the battery is taking a charge and holding it. I definetely know the last battery was bad. Im still waiting to take a look at the grounds. If for some reason i dont see the ground from the driver side head to framerail, can i make another one?
If it's gone, just pick up a 24" generic braided ground strap from any auto parts store and bolt it to the ICM stud and down on the framerail just above the swaybar mount.
Attached Thumbnails Rough idle=optispark?-coil_loc.jpg  
Old 03-10-2011, 10:58 AM
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Ok as soon as i get out of work today, i will be going to look at it. Thanks
Old 03-10-2011, 02:40 PM
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Ok, so i see a ground wire. It looks like its coming from under the icm going to the framerail under the air box. Thats all i see. I took it for another drive today and it was fine until i got on it. It started to choke again. It didnt die out though. It was idling rough for maybe 20 secs, then i slammed the gas again and it cleared right up. It still drops rpms for a split sec if i jab the gas. I pulled the codes. They are 42, 23, 48, 36. I have another thread posted about those. Someone chimed in saying i have a ground issue. I just dont get why its runs fine for a while then decides to run rough. Wouldnt a ground issue be all the time? It seems so intermittent(sp?).
Old 03-10-2011, 02:55 PM
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Originally Posted by 95chevyz28
Ok, so i see a ground wire. It looks like its coming from under the icm going to the framerail under the air box. Thats all i see. I took it for another drive today and it was fine until i got on it. It started to choke again. It didnt die out though. It was idling rough for maybe 20 secs, then i slammed the gas again and it cleared right up. It still drops rpms for a split sec if i jab the gas. I pulled the codes. They are 42, 23, 48, 36. I have another thread posted about those. Someone chimed in saying i have a ground issue. I just dont get why its runs fine for a while then decides to run rough. Wouldnt a ground issue be all the time? It seems so intermittent(sp?).
23: Intake Air Temperature Sensor Circuit High Temperature Low
36: High Resolution Pulse Circuit
42: Ignition Control Grounded Circuit
48: Mass Air Flow Circuit

Sounds like either a ground issue or a changing issue to me.
Your car is dying because it's unable to determine how much air is entering the system
(and thus unable to calculate how much fuel to add).
There are a handful of grounds built into the wiring harness that run up the driver's side of the intake.
Make sure they are clean and connected to the ground post under the ICM.

Take the big braided ground strap off; clean it and every other piece of metal that connects on that stud. Applying dielectric grease may help as well.

I guess it could also be a vacuum leak ... probe around and see if you hear any hissing.
Old 03-10-2011, 02:59 PM
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Ok will do that tomorrow. I will try and look closer tomorrow but like i said, i only saw one braided ground wire coming from what looks like under the icm going to the framerail under the intake box. Could it hurt or help if i put another ground there? Also, would this cause such a intermittent problem? Thanks for your help bud. Mike
Old 03-10-2011, 03:06 PM
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Originally Posted by 95chevyz28
Ok will do that tomorrow. I will try and look closer tomorrow but like i said, i only saw one braided ground wire coming from what looks like under the icm going to the framerail under the intake box. Could it hurt or help if i put another ground there? Also, would this cause such a intermittent problem? Thanks for your help bud. Mike
It probably wouldn't hurt, even if just for diagnostic purposes.
I used to run one from the alt mounting bracket to the ground post because I had similar problems.
Once I cleaned the ground strap with sandpaper and electronics cleaner, I found that the extra ground wasn't needed.
Old 03-10-2011, 03:13 PM
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Ground post on the battery? Yea i figured it couldnt hurt. What about the big 3 upgrade? Would that solve my grounding issue? I will definetely clean the ground wire off tomorrow though and hopefully that solves my problems. Mike


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