sweetride45

I've recently rebuilt my engine. It's a '90 Firebird w/ a '95 LT1/4L60E conversion. It's been bored/stroked to a 383 w/ ported/polished stock heads and CC503 cam. I have been using it for about 2 months. I have roughly 2k miles on the engine. It has a mail-order tune. Every part on the car is new. I purchased the Delteq while I was building the engine (to incorporate it into the build). So, I've had it longer than it's been used. I have a new Opti as well. Initially it started right up and had very crisp and accurate throttle response.

Now the problem has showed up recently. It barely wants to run while trying to start. It is missing/popping/backfiring while idling at a very low 400rpm. My IAC valve is maxed at 160. I checked and the valve is operational. If I crack the throttle blades open (tps still in spec), the IAC will back off to around 30-40 but it is still running very bad. If I give it over roughly 40% throttle, it seems to "clear" and the throttle is GREAT and runs STRONG. I would bet this means the plugs/wires/coils are all working. My MAP is reading low/high 70's at idle (even when at 800rpm). There is no vacuum leaks that I can see. I checked every hose. My plug gap is .050 w/ Autolite 104's. I am using Accel Extreme 9000 plug wires. Fuel pressure primes to 47 +/- and holds steady. So, I doubt it's fuel delivery. I don't know about bad gas. But up high it's a monster, so if the gas was bad, I think it'd be throughout.

The Opti-Box flashes with ignition and stays constant during cranking and when it finally is running (however bad it is, LED stays constant). I do not have any engine codes (Aside from occassional DTC 33, which is for the high MAP voltage due to low vacuum, due to the engine running so low.

I suppose my question comes down to, would this point to the Opti/ICM/Opti-Box/Coils? I wouldn't think it's ignition related, but I would greatly appreciate any insight that you have. I have had the system longer than a year, but have only used it for 2 months/barely 2k miles. I can't see these systems failing ALREADY.

My MAF shows it's passing 14-18 afgs thru datamaster at around 800 rpm or so. That seems pretty high to me. It's the old MAF that came w/ then engine when I got it. It was descreened and ported. pcm4less supposedly tuned for that. However, I know it'll take finetuning to get it right. Shouldn't it be around 10 afgs at that rpm? Could that be why it's running crappy if I crack the blades to get it to "run"? It's tellin' the pcm it needs more gas? The injector duty cycle looked like it was around 2-4, so I'm not sure anymore. They are new Racetronix Delphi 32lb. O2's are Denso.

I'm hearing this "clicking" noise coming from what sounds like the crank area (around the pulley's) when it's running crappy too. All the pulley's are new, but who knows. Would a crappy tensioner bog the engine down like it's doing and making it run $hitty? I really don't think so, but who knows. I'll have to look at that later today.

Any insight on possible bad gas? I'm trying to look for an easy solution, as I've gone thru everything w/o any success yet.

Cleaned the MAF...no change. It will not run (never DID run) w/ MAF unplugged. Bought a Cardone PCM, no change. Reset it many times. The IAC is working, b/c I had it fully extended, PCM requested 160, I took it back out of the tb, and it was pulled in. So, I know it's moving.

I can't think of what else would NOT make the idle go higher. Only thing that logically makes sense to me is that the MAF is saying more air then what it's getting, and the PCM is flooding w/ the injectors. I had the same readings on the MAF though when it DID idle, so I'm grasping at straws.

You know what I DID notice though...When it "somewhat" ran just a bit, I started getting feedback from the O2's (still not closed loop) and they were kinda stayin' in the 900's...When it "finally" went into Closed Loop, they began switching as normal...injector duty cycle around 2-4...b/c I can definately smell the gas when it's poppin' and backfirin' and not ideling smoothly...and it would get so rich to burn ur eyes shortly.

Best way to diagnose injectors? Pressure stays constant w/ Holley afpr and Walbro 255 is pushing out good.

Any suggestions? I'm going crazy!!!

Purple Poncho

iTrader: (1)

Any luck on this?

98pontiacfirehawk

It seems to me you system is running lean if it is burning your eyes. It's like your system runs lean then the pcm tells it to open the injectors to max causing the stumble and terrible idle, if it is backfiring through the intake it's running lean. I had something similar happen to me and it was the O2's that went bad, the pcm said they were correct but they were not. I am saying do not trust the O2's, unplug the O2's and check to see if it idles correct and to see if the backfiring stops, O2's are build cheap and sold at a terrible price. Also, what is your timing doing during all this??