My car has always had random missfires and backfires from the engine, occasionally through the exhaust as well, but it also develops issues where it runs rough and dies or nearly dies and clears up on it's own. The performance has always been inconsistent and it's been worse lately.

Here's the datamaster file

http://hotfile.com/dl/131825892/a176000/run1.uni.html

for the record the dtc codes are tps low, which I thought I took care of already, the voltage is in the correct range and the other is A/C related and I have ripped the A/C out of this car.

 

Nothing obvious on the trace, you are getting a lot of knock retard 5-7* whenever you touch the throttle. Will rob some power but not cause missing or engine dying out. Since knock shows at even low loads of 7% TPS could be a vibration. BLM's are not perfect, but not bad enough to cause the problems you are experiencing. Sounds like ignition related, ICM, coil, rotor, wires, plugs ?? Opti last as you are not getting any codes from it.

 

thanks bob, I cleared all engine codes and gave it a few more runs. I readjusted the tps but I think the TB sticks due to blades being slightly too big so it still isn't right.

http://hotfile.com/dl/131916283/a66019e/run3.uni.html

http://hotfile.com/dl/131916342/b9ec...drive.uni.html

It misses/backfires in the last 1/4 of run 4.

I pulled a few plugs and they look fouled (black carbon - smell like fuel). These plugs are ngk tr-55 stock gap and heat range with 20k miles on them. I guess I'll give them a change and see how that goes. With shorty headers it could take all day just on the pass side, lol.

 

I mentioned ignition in my last post and forgot fueling.. Looking at run 4 log near the last half of log it looks like your O2 voltage started out good when you hit PE mode (WOT) they were steady in the high 800 to 900 Mv range indicating a richer mix or lower AFR for PE operation. But then both o2's went lean down to the 2-300 Mv range after you hit about 52% injector duty cycle. That indicates you may have lost fuel delivery, I would suggest getting FP gauge to verify correct at idle pressure first and then WOT pressure under load when running..

 

I checked fuel pressure recently, turns out I'm a bit below spec. 30 prime, 37 idle, 42 with the fpr vac line pulled. Also recently the pump primes for almost 15 seconds before shutting off instead of the usual 3-4 second cycle. Already ordered a Racetronix pump, what's in there is a cheaper Granatelli. Would this contribute to all the knock I'm getting and cause plugs to foul over time?

Thanks a lot bobdec, you really helped alot.

 

The 15 second fuel pump running when key is moved from off-to-on is something I have never seen. When the PCM sees +12 v ignition-on it boots up and part of the start-up software is to check VAT's and then pick the FP relay for 2 seconds. Later on , when it senses OPTI pulses (correct RPM) indicating the engine is running it then picks and holds the FP relay on until the OPTI pulses stop (engine not running). Since PCM failures are very rare I would almost suspect you FP relay of hanging up (welded/sticky points). Or maybe the +12 ign-on to PM voltage is bouncing, but that would kill the engine completely.
As far as knock goes you are picking up knock count and retard all the time whenever you hit the throttle even sitting there in neutral and goosing the pedal. The BLM's don't indicate a lean condition, it's hard to guess if your loosing fuel , since you have 37 at idle it does not look fuel related. Knock or pre-ignition usually does not occur at no load MAP=48 (high vac) TPS=0.8-1.2% (low/no throttle) at 600-700 RPM. So it's looks to be false, valvetrain vibration or maybe exhaust vibration caused. Have you noticed any vibration noise ? Have you tried a LT4 knock module ? Also noticed your timing looks stock so during the WOT run 95 MAP 3100 RPM you are running only 27-29* actual advance after the PCM takes away 5-6* in retard (stock setting is 33* to 34*) , I run 34-36* with my hot cam, not sure of your cam specs, but the 5-6* retard has to be pulling your top end performance down a bit..

 

I didn't know until recently that high performance fuel pumps like the granatelli and the racetronix I will be putting in really should have upgraded wiring too, apparently they eat up stock wiring because it can't keep up with the demand. That may explain odd behavior of the relay. I went ahead and ordered the racetronix wiring harness upgrade too. I know the fuel pressure isn't totally off from spec, but it is a tad low and I'm not sure about the health of the pump. The last time it stumbled real bad and nearly died, I let it sit a while then decided to try to drive home. When I made it home I noticed the pump was whining very loud at idle, and also surging with the idle which was also surging. A few days later during testing it no longer made any loud noise other than the normal level that I usually don't hear over my exhaust anyhow. I may look into either new injectors or cleaning them, as the injectors likely have 158,000 miles on them (motor rebuilt by speed shop around 120k miles)

This is my cam - http://www.summitracing.com/parts/CR...4&autoview=sku

It has 214 intake 220 exhaust duration @.050 lift with a .452 intake .465 exhaust lift. It's very mild, the engine builders picked it, barely bigger than stock. I have stock rockers, yet my valvetrain sounds like full roller rockers, louder than when it was stock. I do have forged pistons if that makes any difference. I've had the valves adjusted before because I thought they were too loud, but after adjustment (including once done by myself, they didn't sound any quieter. I have an LT4 knock module in there, put it in there when the head gaskets blew at 12k miles. I'm now at about 34k. I'm guessing exhaust vibration would only be caused by loose bolts in the head to y pipe area? What about an exhaust leak? A few months ago I had to cut part of my y-pipe and weld it back up to remove the starter as my whole system is welded, and the y-pipe can't be dropped like normal. I'm not sure how well I welded up the top portion of it as it was more difficult to weld than anticipated. But that was fairly recent and I've been having problems since I got the motor built, even before.