Mindgame

This one has me scratching my head real good guys....

Friend brings me his 97' Firebird today because he'd like for me to take a look at it and help him find the source of a "miss" that just cropped up over the last couple of days.

Just so everyone knows where we're at here let me tell you what the car has done to it and all the other pertinent little details....

Car is an M6 with stock shortblock & ~108k on the odometer. It has a CAI, CSR pump, Trick Flow elbow and a catback exhaust system for modifications. Opti, coil, ICM, ECU, TPS, IAC etc are all original 108k mile factory components.

Ok, so the car starts up just fine and idles smooth. Problems come when we come off-idle @ ~1200rpm and start to accelerate. Then I'm getting this heavy miss that just about kills the car but never really stalls it out. Clutch it to get the revs up and she'll usually recover although the "miss" comes back anytime you try to throttle it heavily at lower revs (~2000). It does this intermittently though. I noticed it when hot (~210º F) and I noticed it doing the same thing when the engine was ~180º F. Launch the car at ~1500 rpm and you can usually get away ok.

I did a few check-ups to eliminate some of the obvious things....

Cleaned the MAF and throttle body, checked for vacuum leaks, checked coil continuity, checked the PCV valve and even went as far as plugging the EGR port to see if that cleaned it up. Well, the EGR was my first guess and that being an easy check I just plugged the port at the manifold and took the car for a drive. Seemed to help the off-line problem but we still have the heavy miss at high-load (Didn't really drive it enough to see if it really helped the off-line problem). I went ahead and got the ICM spaced away from the head just to kill another bird. Didn't expect that to fix the problem but it needed doing anyway so I did. Didn't help.

So I'm going to crack into this thing tomorrow morning and do a few things that need doing anyways like spark plug wires and new plugs. ANY suggestions you guys can throw my way will be of great service to me. May save me a lot of time and headache if you've been down this road already.

I'll retrieve codes (SES is on due to an O2 sensor) tomorrow and go from there but would appreciate your input.

-Mindgame

revtime

For what its worth my car had basically the same symptoms when my cap and rotor needed to be replaced.
Its an auto but at temp it would stutter under part throttle, once you gave it some gas it would come out of it.

Cmr0z28

CSR pump makes me want to say opti...it's real easy to get coolant on the opti during a WP install as we all know, so I'd have a look at that.

Mindgame

Thanks guys,

Checking the cap & rotor is on my list of checking items. That'll give me a chance to look the optispark over too.

Noticed this morning with the engine dead cold that the off-idle stumble was non existent. Leads me to believe it's an electrical issue with heat exacerbating the problem. Have a lot of digging to do today.

-Mindgame

simple

MG, hows fuel pressure?
stock pumps are about as good as the opti's location

96LT1TX

i would say change fuel filter... sounds like that to me but opti would be next on my list.

marshall93z

Will it idle, or does it die when you let off the gas?

MattysTA

i Have a 97 trans am that had the same problem change the 02 thats giving the code. it will cause that problem, Thats what my problem was but it took months for me to figure it out because it wasnt failing enough to throw an ses code but enough to make it run like **** and it would come and go

Mindgame

Fuel pressure checks fine at all loads. Filter was replaced ~500 miles ago.

marshall,
No, doesn't die. As soon as you get off the throttle it stumbles a little then idles just fine. Hasn't stalled on me yet knock on wood.

Matty,
We'll have a new 02 sensor in there tomorrow evening and see where we're at after that.

Still have a few more items to check....

Thanks again.

-Mindgame

'96WS-6

I was having the same exact problem (see my other thread) replaced the ignition coil...did not solve problem so i went searching around and looky there...the guy at the gm dealership dint do too good of a job puttin my wires on and 3 of them were resting on my manifolds...so i looked at the and they are somewhat burnt so im goin to the dealership tom to get some new wires put on for free...cuz they are warrantied...but rite now i temperarily solved my problem by using a good ole zip tie...so with it being heat related ur spark from the wires or possibly old opti is arching under load and heat and thats where ur problem is...hope this helps
Vince

mongse_1

I'd check O2s and for any leaks in the exhaust system before the O2s. I had a similar problem on a '94 that was stock except for a DIY single turbo. On cold startup, the car would run fine and boost up w/o a problem. As soon as it jumped loop & started reading off the O2s, all hell broke loose. Changed the O2s and the problem was almost non-existant. I did have a small problem w/ an exhaust leak @ the DP flange, but that was easily fixed.

CamaroSS30thAnn

ding ding ding

if its a front one then there ya go , thats y these cars have an SES light to help u figure the problem out so u dont have to go through all that crap

besides it sounds like what my car wa doing when it had bac 02s

96speed

MG: Does it ever do it when the car is in open loop?

Like mentioned, this sounds like an O2 sensor problem I had. Luckily, I had a Scanmaster and noticed that every now and then an O2 value would "hang." No code though (even with a more fickle OBD2 pcm). New set of O2s, no more cough, chug, spit, OR sputter .

Ryan

Mindgame

My apologies guys.... I got really caught up in this one, went to work on it and then forgot to post my findings.

Well, instead of guessing about all this I went and got autoxray back from my buddy (the one that borrows things and keeps them till I come and get em'). Turns out you guys were right on with the O2 sensor. The sensor showed a flat spot where it failed to respond, kind of like what Ryan was saying his did.

Just in case other people are following up on similar problems....

I initially thought to check other things simply because the owner had informed me that his SES light (DTC -whatever for right front O2-) had been on for the last two months. The car hadn't run abnormally until the last couple of days before I got it. AND I'm not afraid to admit that I, not exactly being an EFI guru, didn't think an O2 sensor could cause these kinds of problems. Well I was wrong.

BTW, we took care of the problem with a new O2 in a new set of TPIS headers.

Why not... I mean changing stuff out on these cars gets you half way through a header job anyways.

Thanks for the help guys.

-Mindgame

CamaroSS30thAnn

^^^ yep when my 02s went it overloaded teh cylinders on teh left bank fouling out teh plugs, car would runa nd idle bad but would pop and backfire and have problem moving under load

good to c ugot ur problem down