So on the way home last night my Service Engine Soon light was flashing for a few seconds. I get home and its a P0300(random cylinder misfire). This isn't the first time this has happened. Car seems to be running fine except for this. I also have timing being pulled from knock retard, which I believe is false. And every once in a while my scanmaster will act weird, like it has a loose connection. It will randomly reset itself and the little recording light will light up sometimes even under part throttle conditions. I don't know where to start looking. I don't believe I have any bad grounds. Is there any way my PCM would be causing this, can a PCM be bad and still work most of the time? I had it reflashed a few months ago when it was on the dyno, mostly messing around with AF ratio. I figure if it was the PCM, it wouldn't be random like this. Anyone have any suggestions?

 

Common causes would be plugs, plug wires, opti.

 

Plugs and wires are less than 3-4 years old with less than 30,000 miles. They are TR55IX iridium plugs and MSD 8.5 wires. Opti is an original with 90,000 miles and if it is the opti, I'll just wait until the new motor goes in and switch over to a LS1 ignition.

 

The recording will initiate at less than WOT. IIRC the threshhold is 75% TPP. That may be pointing to a problem with the TPS sensor, if the throttle is not actually 75% open. Might be worth checking it out.

How much knock retard are you getting, and under what conditions?

 

The knock retard is completely random and I see up to 18º. I've been meaning to go down and have it datalogged on the dyno, but haven't had the time. And the scanmaster is randomly shutting off, kind of like a bad ground or something. The recording light fill flicker once in a while, not like it is actually recording.

Something else I noticed that might or might not be related. The Low Traction light will randomly flash a few times. I've also witnessed it flickering, as in not coming on all the way, just a little flicker. I recently installed a build 4L60E and 12 bolt rear end without ASR and ABS so not my ASR OFF and ABS INOP are always on. I don't know if that has anything to do with the Low Traction light though.

 

18deg of knock retard are you 100% sure it is false knock? exhaust rattling? loose motor mount? have you tried putting higher octane gas in to see if it clears up?

I would also check and recheck all of the grounds since things are flickering

 

I've checked all the grounds I could see. I ran 100 octane on more than a few occasions and still have got knock retard. My tuner says we are running stock timing. Motor mounts are tight, and the exhaust doesn't rattle or anything. I though I heard some abnormal motor noise while I was under it a while back when it was running, but it didn't sound significant and I couldn't pinpoint it.

Sometime the knock retard can be replicated under high load, but sometimes its just completely random and will show up for no reason.

 

check the wire for the knock sensor or maybe even swap out the knock sensor. I have never heard of that much knock retard so im thinking there is something faulty in that circuit. Someone else may want to chime in on this though..

 

try getting a lt4 knock module...my stock one was retarding my timing just after switching my exhaust and headers and that took care of it.

 

I didn't think stock programming allowed more than 15* of knock retard.