'96 LT1 T/A bad miss fire got worse.

[SMok3 Em A11]

This is the deal, My water pump went so I pulled it and in the process broke the gear shaft off the timing chain cover. Well at the time not knowing what I was getting in to I made the decision to put it in the shop to have it put back together.(mistake as it turns out). Well when I got it back It ran fine till it warmed up and then the missfire and eventual stall out started. Well Since then I have replaced- CPS twice, Distributer, cap, rotor, wires, plugs, egr(now deleted), intake elbow and added cold air, tried 2 different MAF sensors. I had the ICM tested and spaced the coil away from the block. I also pulled the intake mani off to have it cleaned and I painted it. deleted the A/C as well. I know some off these things may nt make a diference but just wanted to be clear about everything. After I put it back together this time it seemed to be fine for a while then it all started again. So if anyone can help please do or send me somwhere that can thanks.

[96LT1355Z28]

-Have you double checked and made sure all your plug wires are routed to the correct locations and secured on the cap/plugs, including the coil wire?

-Are all the harnesses pluged in on your TB and did you mess with the TPS at all when the manifold was off?

-Have you verified you don't have any vacuum leaks?

-How does your opti harness look?

-You mentioned in a PM that your exhaust would glow is it on one or both sides?

-Hows your fuel pressure?

-When it runs what happens if you try to rev it up, can you keep it running this way?

[SMok3 Em A11]

-Have you double checked and made sure all your plug wires are routed to the correct locations and secured on the cap/plugs, including the coil wire?

-Are all the harnesses pluged in on your TB and did you mess with the TPS at all when the manifold was off?
I never touched the TPS this was 1 of my next moves if I cant figure anything out and yes everything is plugged in.

-Have you verified you don't have any vacuum leaks?
I am pretty sure I dont have this prob when I did the egr air delete I rerouted everything to work i accordance with a similar car with similar set up.

-How does your opti harness look?
the wires are fine but the long plug that goes to the opti has a chip in it new 1 on the way so will update when it comes in.



-You mentioned in a PM that your exhaust would glow is it on one or both sides?
It usually starts on the even side(passenger) and as it warms up both but not all the time.

-Hows your fuel pressure?
Not sure dont have a gauge. How could I check without 1?

-When it runs what happens if you try to rev it up, can you keep it running this way?
Now throttle does nothing but make it stall. B4 when it actually ran, after it warmed up if i gave it any throttle it would just bogg out and backfire but would idle fine. now only idles at about 500 rpms very roughly.

[96LT1355Z28]

No way to check fuel pressure without a gauge. If you can borrow or rent one it should be 43-47 psi at idle w/o vacuum line attached. Also try turning the key on and watch the gauge as the pump primes, don't start the car and watch to see if the psi bleeds off. It should hold for several minutes and slowly begin to go down.

When is the last time you replaced the fuel filter, if it's clogged you can have adequate psi but not enough flow.

TPS voltage should be at .67 volts with the throttle closed, .67 isn't exact as others have acceptable idle from .62-.72. This can be measured by probing the signal wire from the TPS but it's easier to check with a scan tool, and you have less chance of damaging the wire.

The exhaust glowing and the backfiring are both signs of a lean condition. Plus when you open the throttle to give it more air it stalls which makes me think it's not getting enough fuel. It could also be a late timing issue but that's unlikely, hopefully the new harness will make a difference. Getting your hands on a scan tool really aids in diagnosing these cars since you have no other way to monitor fuel trims, O2 activity, and timing.

[SMok3 Em A11]

Update!!!!
Pulled a few of my plugs and they were solid black Im not a genius but thats a rich condition right I am so damn confused.

[Tarheel'Z']

the symtoms you describe are exactly what my car did when the factory opti took a crap many moons ago
im afraid im not gonna be much help since you say you changed opti,my car would run fine until it got up to temp and then backfire and pop and go crazy until it died,,after cooling off for a while it would start back up and do it again
i changed cats,filters,sensors etc before finally learning about the dreaded opti,

hope you figure it out

[SMok3 Em A11]

Yea dude what you desribed is exactly what mine did to the T. But the entire ignition system is new thats what is throwing every1 with an idea way out of wack. thanks tho.

[96LT1355Z28]

Black plugs are a sign of it running rich, it's kinda weird rich and lean can have the same symptoms popping, rough idle, eye burning exhaust smell, etc! Sorry, I should have suggested you pull the plugs eariler to see what they looked like. Just double checking you did replace the opti and not juts the cap and rotor, correct?

[SMok3 Em A11]

No worries bro everyone I have talked to about this has had a different answer. Yours was differnt than others so your suggestions were considered I just happen to pull the plugs first LOL as soon as I saw them I knew it wasn't leaning out. Although I still havn't figured a thing out. To answer your other ? Yes it is all new Opti, cap, rotor, and wires (twice since I BBQd the #7&5 wires). had the ICM tested its good.

[96LT1355Z28]

Any luck getting a scan tool and looking at your fuel trims and O2 sensors?

[SMok3 Em A11]

I did have it plugged up to a $2000 scan tool a friend had, but the only thing is I had the batt. unplugged a couple hours b4. It showed no codes and I cant keep it runnin long enuf to reset the pcm?

[SMok3 Em A11]

WELL today I fixed yet another burnt plug wire and 2 vac leaks(opti fresh air, and pcv hose was broken under the throttle body). And the survey says......not a damn thing it is still exactly the same. Also sprayed carb cleaner around the intake to check for leaks and also nadda?

[96LT1355Z28]

Did you get a new opti harness in it yet? The car did run okay for awhile after you got it back from the shop correct? I was just thinking if not they there may be a timing chain/ cam timing problem. Have you tried a compression check to make sure all cylinders are building equal psi? :(

[bidicamaro]

If you're cranking it and not getting it to run but you're having fuel make it in the cylenders that will foul out the plugs. Have you checked and rechecked the proper routing of the plug wires? Also, I'm going out on a limb here but maybe you ended up getting an opti that was doomed from the day it left it's journey out of the manufacturing facility. Did you also make sure that the opti was put on correct? I don't know about the other styles but mine is just splined on and can be put on any way you feel. Hope you get it going again!!

[SMok3 Em A11]

it will run but not well and i have pulled all the plugs twice and 5xs checked the wires. Also replaced 3 burnt wires along the way and strangely nothing happened. Also found a couple vac leaks and also not a single change. After I got it back from the shop it did run but only until it got to running temp. then it would putter out eventually. After rplaceing many parts includeing the opti it ran fine for a while got to temp no miss fires nothing. Drove it a few miles and it over heated a little and from that point on it runs rich as hell and has no throttle advance. not sure I am going to have the car scanned again last time the battery had been unplugged to soon before the scan so got nothing.

[SMok3 Em A11]

Oh as far as the opti being out of wack my opti has guides so that it doesnt go in wrong only fits 1 way

[bidicamaro]

Is the ECT on the waterpump good? From what I've learned and "experianced" when that is bad it throws a temp reading to the ECM of -40* (give or take) wich the ECM turns on the fans and runs the car as rich as possible. Also, have you made sure that the coolant was free of air last time you had the water pump off using the bleeder screws? If it got to hot bad things tend to happen. another thing, you said you deleted the EGR. did you block it off or how did you do that?

[SMok3 Em A11]

Is the ECT on the waterpump good? From what I've learned and "experianced" when that is bad it throws a temp reading to the ECM of -40* (give or take) wich the ECM turns on the fans and runs the car as rich as possible. Also, have you made sure that the coolant was free of air last time you had the water pump off using the bleeder screws? If it got to hot bad things tend to happen. another thing, you said you deleted the EGR. did you block it off or how did you do that?


Ok well the ECT was the very first thing I had replaced. we scanned it again yesterday and found that the MAF was reading over twice wht it should at idle. Which make sense because if the pcm is being told that there is alot of air when its not there then it would dump fuel to compensate. But here is the reall kicker I put a different 1 on and as usual nothing changed??????

[grn95t/a]

heres a little run down of what we seen that was way out of wack readings wise...


maf reading key on/engine off 10gms ( should b 0gms i belive )

maf reading while cranking 20gms

maf reading while the engine tries to run 21-25gms ( should be 2.5-9 while idling )

injectors while cranking 32ms

injectors while running 35.2ms ( should b 3.5-5.5 )

of course the LT's and ST's where way out of wack and the O2's where stuck rich.

coolant was around 50f when we started and rose to 102f for the little time it ran, so that appears to be working. the map appeared to be reading correct.

i am leaning towards some bad grounds, a bad spot in the harness or a pcm??? i have a pcm where gonna swap in to see if that works. a good maf was swapped in with no better results. anyone else have any ideas???

[SMok3 Em A11]

heres a little run down of what we seen that was way out of wack readings wise...


maf reading key on/engine off 10gms ( should b 0gms i belive )

maf reading while cranking 20gms

maf reading while the engine tries to run 21-25gms ( should be 2.5-9 while idling )

injectors while cranking 32ms

injectors while running 35.2ms ( should b 3.5-5.5 )

of course the LT's and ST's where way out of wack and the O2's where stuck rich.

coolant was around 50f when we started and rose to 102f for the little time it ran, so that appears to be working. the map appeared to be reading correct.

i am leaning towards some bad grounds, a bad spot in the harness or a pcm??? i have a pcm where gonna swap in to see if that works. a good maf was swapped in with no better results. anyone else have any ideas???

thanks again for the duplicate post LOL.

[bidicamaro]

Have you checked the ground wires that are on one of the coil mounting bolts? If the maf goes out I always thought the PCM reverted back to the map and ran as speed density?

[SMok3 Em A11]

been getting alot of hits on the forums about ground wires the weather was bad yeasterday so I didnt have a chance to check but I will today and will update.

[grn95t/a]

find anything homie?

[SMok3 Em A11]

find anything homie?

Naw was had a lazy day played hooky from work and slept in. LOL 2 mar for sure. be here with no ride. so why not??

[96LT1355Z28]

Any updates?

[SMok3 Em A11]

Didnt find any loose wires but im starting to get alot of nays on the obd1 pcm on the obd2 setup.

[grn95t/a]

ya, but its still worth a shot dude, only takes 5 minutes to swap'em out and aint gonna hurt nothing...unless china on the run at the wrekn yard would let ya use the one out of the crashd convertable??

[SMok3 Em A11]

Maybe but he wants an arm and a leg for that thing and prolly wouldnt let it go with the cash.

[grn95t/a]

i see, damn junkyard dog, lol. well isay we still try my obd1, just to see if it fires and runs better.

[wysemunky]

I just sorta skimmed through but from what Ive read im leaning towards it being either the MAF, the O2 sensors or plug wires. A few months ago my car was having "random misfires" once it warmed up, it would run good when it was cold then when it warmed up it would miss and surge at lower rpms. I changed the plugs and plug wires and its been great ever since. I found 2 plug wires that were cracked and broke when in the process of removing them, a couple of the sparkplugs even appeared to be the original acdelco's.

[bidicamaro]

...a couple of the sparkplugs even appeared to be the original acdelco's.

Let me guess, the one's on the passenger front or the #3 or #5? They seem to suck to get out. Last time I did plugs I just pulled my headers off. Seemed to save some time.

...back to the subject at hand...

[SMok3 Em A11]

todays bump

[IronOutlaw]

Gut your cats.

[SMok3 Em A11]

I got it after much thought. I bypassed the TB coolant line but originally did it wrong. The cause was the line on the passenger side built too much presure and busted. So the brand new opti I bought was screwed as it turns out. New opti under warranty and new cap and rotor and poof problem gone. Thanks guys for the input I really appreciate it.

[Tarheel'Z']

awesome man gotta love it

[grn95t/a]

wow dude you know you really dissappoint me. all the help i gave ya, and the time i spent, and the tools i loaned ya, and you cant even give me a single ounce of credit. its absoulty amazing, tottally baffles me that you wouldn't give me some props for helping to bring your heap back to life dude. all i keep reading on these forums is I , I , I. all i can say is wow.

[SMok3 Em A11]

Dude really sorry you feel that way. You were a very big help and I meant no disrespect really. I acctually just text you a couple hours ago thanking you and then I see this. I feel really bad dude sorry. Thats also why I offered to help with the verter saturday. I was tryin to pay you back in some kind of way. I may not have posted it but I have been nothing but grateful. Really am sorry bro.

[96LT1355Z28]

It didn't leak any coolant on the ground and give any clues? Glad you guys got it figured out!