wow lots of great info! I have lits of work to do! thanks all I will post all info when i get a chance. i am on weekend 12 hr shifts now so i guess i will be working at night on the car. thanks again.

 

ok this is what I got tonight from scanner, all were taken at idle with engine at operating temperature.
-engine load 4%
-coolant temp 174*
-short term fuel trims, both banks 0-2% average and fluctuating up and down a few points
-long term fuel trims, both banks fluctuating up and down from about -9 to +8%
-map sensor reading 10inHg steady
-12* timing advance but moving up and down
-IAT 92* (kinda warm in sc!)
-Maf 1lb/min and when I raise the rpm and hold it steady about 2500rpm it will read about 2lb/min
-upstream o2 sensors both banks .005-.795 and fluctuating drastically!
-tps sensor reading 0% and will rise if I increase the throttle.


I unplugged both of them afterwards and the car was not any better, so I unplugged the MAF again (after I shut the car off) and fired it back up still no better. WTF?
So it seems I have ruled out the MAP, MAF, TPS, and engine temp sensor.
Now there is something that seems odd to me, while the car is trying to idle I think I can hear the IAC trying to control the idle and I can hear hissing when the engine starts to stall. So thats what I have......any thoughts?

 

Eh, okay. That's not terribly helpful on the surface, but we'll get there eventually.

It's hard to make a call at this point. Nothing you've listed really helps narrow it down. This is when I'd start pulling all the plugs, keeping them in order for inspection -- you need to find out what cylinder(s) are having issues. If you don't find a specific cylinder having trouble, then look for things further back that can cause a random misfire (ignition coil/module, optispark, possibility of a shoddy Walbro pump or electrical connection). Make sure all of the fuel injector electrical connectors are on good and tight.

Anyway, here's another book for you:

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(1) You'll have to be more precise on the LTFTs. They shouldn't be "fluctuating" very quickly -- the trends should be relatively stable. Don't mess with the throttle, just read both banks at idle and post their respective percentages. (Different load/throttle conditions will jump the LTFTs into different memory cells, and that isn't very helpful here -- we just want to compare left/right bank LTFTs at idle only).

We're trying to find out if one bank is running richer or leaner than the other at idle. At first glance, those percentages translate to BLM counts between 116~138, but you didn't cite their respective banks. For reference, they bottom out at 108 (computer subtracting about -15% fuel for a perceived rich running condition) and max out at 160 (computer adding about +25% fuel for a perceived lean running condition). Your target air/fuel ratio is being corrected back to normal 14.7:1 between that range -- but outside that range, the computer can't correct for it, and you'll have a physical rich or lean running condition. The trends help us know what's going on and locate problems, because both banks should be identical.

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(2) Spark timing seems low to me. Might be the computer pulling timing due to perceived knocking from the rough running condition. You said earlier that it's backfiring -- did you mean out the intake (a technical "backfire"), or just popping noises in the exhaust (unburnt fuel igniting in the exhaust)? Any excessive 'clacking' noises coming from underneath the valvecovers?

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(3) 1 lb/min MAF reading translates to about 7.56gps. Fairly normal. Based on the fact that it runs the same with it connected or disconnected (speed density mode), I'll assume for now that the MAF is not the cause.

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(4) You said you disabled EGR? What about EVAP? How exactly did you go about doing that? Just a wild guess, but if you're hearing hissing noises only when the engine stalls, perhaps you left one of the EVAP or EGR control solenoids' electrical connectors connected and vacuum ports open? That would, in effect, create a vacuum leak only when the computer called for those systems to activate, triggering the solenoids to open. If you haven't already, be sure to disconnect their respective solenoid electrical connectors (which will probably throw a diagnostic trouble code / SES light) and cap everything off.

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(5) Probably should have asked this first, but did you do ANY other work to the car (aside from the fuel pump) prior to this rough running condition? Or did it just happen out of the blue? It's always a good place to start looking at anything you've messed with recently. Get back to us on those fuel pressures.

Check for burnt spark plug wires -- pop the hood at night and look for any blue arcs of light.

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ok first the LTFTs are fairly stable at idle, maybe plus or minus 5%.
I deleted egr when I done the headers years ago, not the evap to my knowledge.
Now to the backfires, the car will backfire in the exhaust when I let off the gas (6 speed with clutch out and in gear). When the car stalls most of the time it will backfire through the intake. The only previous work was that I changed out the opti harness because it had a broken clip and would back out not allowing the car to start. Ran when when I installed that. Then the fuel pump quit on me. The fuel pressure seems fine with 42psi at idle. I will remove plugs tomorrow I guess when I get off work. Oh yea plugs and wires in good shape fairly new and not arching.

 

Ken, the above sentences are almost entirely worthless for diagnostic purposes. That's okay -- it's no big deal -- but there's little point in reporting information back to us if you're going to be imprecise.

-Does the fuel pressure rise above 42psi when you disconnect the vacuum control hose? If not, the regulator is faulty. Finding that delta pressure change is a major component to testing fuel pressure -- you're not done testing yet.

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-Do you see the difference between saying, "the LTFTs are maybe sorta +/- 5% to 9%" versus saying "The left bank fuel trims are -5%, and the right bank fuel trims are +9%"?

The former means nothing. The latter tells me precisely what is happening -- it tells me your left bank is running rich, and your right bank is running lean. It tells me your right bank would more likely have a slight misfire, as that would produce excess oxygen on that bank to be picked up by the oxygen sensor, and the computer is adding fuel to compensate. Even a few percentage points might help us find out where to look.

Anyway, I think I'm done here -- I'll let someone else step in. My best guess at this point is an ignition-related misfire. Clean and inspect that new Optispark harness, and perhaps check continuity between the opti harness to the computer with a digital multimeter. I'd personally ditch those Bosch oxygen sensors regardless -- get AC Delco.

Good luck -- hope you get it figured out soon.

 

Well after checking the pressure regulator by unplugging it from the vacuum source it raised the pressure to 50psi. I replaced the IAC, coil and ICM. I drove the car and It seemed to help until it died completely and now will not start at all, I had to get it towed back home. The opti only has 10k miles on it, could it have failed already? I used a new ac delco unit when I replaced it. Im lost now and my wife is having to drive me to work and I need to fix my car.

 

in which way did it just die?
will it crank?
did the entire electrical system drop out?
will it start and then die?

 

Yes, optis can and do take a **** all the time regardless of brand or mileage....regardless of what others might say here. There's plenty of stories of new AC delco opti's crapping out in less than 500 miles...same with MSD, chandler, ect. Looks like you might be in for an opti replacement Might as well try doing it yourself and save yourself some cash, unfortunately opti replacement is a fact of life if you own a LT1 car long enough.

 

opti replaced same issue, ordering new denso o2s today. see what that does.

 

check your fuses, mine did that once. it popped the PCM fuse. that is inside the car. but check the ones under the hood too just for good measure

 

will check that tommorow, i am surprised it will even run with that fuse blown

 

died completely and wont start at all was what i was assuming the point you were at. $180 tow bill for a 12 cent fuse. burned me up for days.

 

it has since started back but still wont idle while warm and backfiring while coasting in gear. under throttle no problems. I did find a damaged wire on one of the o2s but was still connected. Waiting on densos now......

 

new denso o2s installed, still has very poor idle. I do have new codes for mulitiple/random cylinder misfire and its the first time these have come up. Could I still have a clogged fuel filter if the pressure checks out fine? Clogged injectors maybe?

 

i would go down the spark path instead of the fuel path personally, unless you pissed off your neighboors and they sugared your gas tank, i doubt that is it, but anything is possible

 

connected a spark plug to one of the wires and cranked engine, there was a consistant strong blue spark so I assume I am getting good spark. If I try to "blip" throttle it will stumble and if I hold the throttle it will die. During all this I have a fuel pressure gauge attached and the pressure does not drop at all. Has anyone had luck with fuel injector cleaners?

 

turns out it was incorrect routing of the opti venting system. I hope this helps someone in a search in the future because it kicked my ***! All good now, I still do not understand why this made my car run like crap......

 

Can you elaborate? Where was it routed?

 

The opti is supposed to have a vacuum line and a vent line so that it pulls fresh air through the distributor. Somehow mine had 2 vacuum lines on it and no vent. Needless to say that did not work too well.

 

so did the opti developed a leak large enough to effect idle?