Hi, please see my sig for mods. My car has 38k on it, and I've been thru the usual crap with fixing stuff after modifications and much drag racing. I stopped racing 3 years ago, and since then, have had no problems. But now I'm now completely losing it. I'm hoping someone can help me.

The car ran fine until two weeks ago. When I left work, it felt weird when I started it up. Mind you, I hadn't beat on it for at least a week. Within a mile or so, it got really bad, missing/shaking, etc. SES light began flashing, and I had to turn it off. Barely made the short trip home.

I scanned for codes & found none; however, this was on a PCM from MadZ28 that tuned out the misfire codes (from my CC305). I switched back to the original computer, and got the usual 0301, which later turned to 0302, followed by 0300 (misfire 1 to 2 to random multiple pattern will repeat after I clear the codes & fu-- with the car some more) No other codes.

Checked wires - no damage.

Replaced all plugs with new AC Delco, 0.050" gap, and no change. On old plugs, drivers bank = sooty, passengers = tan/white deposits (pass side looks normal to me)

Looked at engine in dark after water spraying wires, and saw no flashes, did spark test on all plugs, nice blue spark, regular & not skipping a beat

Replaced wires with original stock set, which had never been burned/or had problems but got replaced when I did shortly headers

Checked FP = 41psi

Attached vacuum gauge, running between 6 - 11 ", very erratic; historically has been 15" & very steady.

Got out tubing/hose, stuck it in my ear, traced the intake, heads, TB for vacuum leaks & found none

Blocked off the EGR tube from the shortly headers

Checked fule injectors with noid light, all OK

Pulled fuel rail, put injector tips into small cups, cranked engine several times for 5 - 10 seconds and compared fuel volume collected for all 8 cyl, all looked equal.

Changed injectors back from SVT 24# to stock 24#, still runs like crap

Did continuity check of all injector wires to source (PCM, fuse), checked all PCM grounds, Opti to comp, REPLACED opti.

Checked valve lash/redid, springs and pushrods = OK

Comp check on 1-3-5-7, 180 - 190psi; have avoided doing 2-4-6-8 due to limited access.

Checked drivers side cat for pluggage, found none, but much soot due to rich condition

Scan tool says drivers bank LT fuel is +25%, ST = +37.5%. Passengers side LT fuel is -25%, ST = -50%

Replaced coil and ICM

Swapped out MAF with a unit I bought on ebay & had removed the screen from (car ran OK on it, but it had triggered a code, so I put it in a box a couple years ago)

Sometimes upon starting, it idles perfect at 15" vacuum for about 5 seconds and then back to the rough stutter/miss, but this is not often.

Checked TPS and IAC per chiltons & passed tests

Probably did other stuff as well, but cannot remember as I am now on my 5th "kill the frustration" beer. Oh yeah, replaced both #1 O2 sensors

Anybody have a suggestion? I'm about at wits end. I don't think it's a blown head gasket because the oil is nice and clean and there's no antifreeze in the exhaust. Runs like crap when cold & runs even crappier when hot.

I've called several places to do a diagnostic test in the past & nobody wants to touch a modified car. Sorry for the long post but I Need Help! Am about to commit Firebird-o-cide and then turn gun on self.

Thanks,
Pooch

 

My suggestion would be to look at the control(s) portion of the fuel management system. In particular, the O2s and their associated wiring.

My feeling is the O2 on the driver side is not switching properly and stays mostly in the "lean" area of it's signal. The PCM interprets this as a "true" lean condition and richens up the AF ratio on that side. The extra fuel fouls out the plugs like you observed and then the misfires occur.

I suggest you try replacing the questionable plugs with fresh ones and disconnect one of the front O2s. Now test drive it and see what happens while it stays in open loop the entire time. If it stays running descent, you know the problem is in the controls and probably in the O2 wiring. It is easy to test for.

FYI, I had put headers on 2 years before a toasted O2 wire problem showed up.

BTW, running rich will screw up a cat.

 

Thanks, Speedy. All plugs were changed previously and I don't have more than an hour time of running the car in the garage since then. It's so bad, I dare not drive it. I did disconnect to drivers side O2 sensor before, and it had no affect, but I agree with you - it seems to be a glitch in controlling the fuel management systems. The O2 values bounce around from 0.1 - 0.9 V, so I didn't think that was an issue, but now that you have me thinking about it, I'll try checking the wires from the O2's to the computer.

I once had a problem with the wires burning on the headers, so I wrapped the headers, and no more burned wires. People say this is bad for the headers, but I think that since they're stainless, that isn't an issue.

Thanks again,
Pooch

 

Stupid question maybe, but did you get a tune when you swapped the cam and heads? When did this problem start and I mean like right after you put the cam in or did it drive for a while and then start. Did you upgrade the fuel pump when you did the work? I doubt that is the cause but I would upgrade it anyway with the cam/head/injectors you have. How bout a blown intake gasket?

 

The car has had the cam in it for 5 - 6 years & 20k miles. The tune was done at that time & the cam never gave me a problem other than constantly setting the misfire code (although it wasn't misfiring - cam surge). I've had it dyno'ed at 338 RWHP, and the fuel was dialed in at 13.2:1 - 13:1 on the wideband. Idle vacuum was lower than stock at 15", but always stable. The thought that the intake is blown is a possibility. Is there any way I could check that out without disassembly? Going to go check the O2 circuitry here in a minute. Need to finish before the Cavs/Pistons game!

Thanks,
Pooch

 

I am having similar probems and today I replaced the ICM, and it seems to have fixed it, (id dont want to get to excited too soon) but as you have done that I would try the ICM/ opti test on shoeboxs site, http://shbox.com/1/4th_gen_tech2.html#opti_test if you have a wire giving you a problem in the icm area it might manifest itself the same as a bad or failing ICM....

 

He!! Yeah! Cavs won in 2X overtime!!! In between time-outs, etc, I checked the ICM (even though it's new) & didn't mess with the coil, it's new too. All circuitry & everything else checks out OK.

This is strange, but could a clogged cat on the passengers side be causing my troubles? Even though the PCM is richening that side and leaning out the drivers side, could this be the cause? It's intuitively opposite to what I'd expect, but... it would only take a small amount of encouragement for me to check that out as well....

Thanks again for all of your guys' suggestions.
Pooch

 

Are you experiencing a big power loss, if so then it could be the cat. If so gut it and see what happens.