Expert Tuners: Need Your Input!

[psychlow]

So I have a random misfire at idle.

Replaced/new
- Plug wires
- Spark plugs
- Transistor pack (ignitor)
- MPI Relay

Checked:
- Injectors - when disabled one by one with my logger, the engine bogs as it should.
- Compression - 120-120-120-130 (I'm at 6,000 ft... service limit is 101PSI, standard compression is 136.)
- With an ignition tester, it'll jump a spark gap of over an inch (click for video)
- CAS harness voltage
- Fuel pressure
- Base timing has been adjusted
- ECU has no leakage whatsoever, and communicates very well with my logger
- Valve timing verified correct (and confirmed by compression results)
- 2G MAS is logging airflow, barometric pressure and temperature correctly
- Coil pack primary, secondary, and insulatory resistance was checked. Replaced with a known good unit anyway, and the problem still occurs.
- Resistance from battery to the spark plug threads is 2.0 Ohms.

I know I have 2 major boost leaks: 1 in the throttle body shaft seals, and another in the compressor housing of my T04B - (I need to pull it and put some high-temp RTV in it). The leaks only affect air/fuel, however - and I can adjust that by tweaking fuel pressure on my AFPR. I can't find a single fuel pressure setting that keeps the engine from randomly misfiring.

So, what else could this be? Has anyone ever known of a random misfire resulting from a bad CAS?

Mods, for quick reference:
Fuel:
- Walbro 255LPH, rewired
- 3/8'' custom hardline from pump to fuel filter, -6AN to rail
- FullThrottleSpeed AFPR, set at around 55PSI to compensate for 2G MAS (but I've been adjusting it to try to get AFR correct)
- Stock 450's (will upgrade before boosting more, don't worry)

Air:
- 2G MAS
- 3'' Homemade intake
- Bullseye T04B V-trim

 

[Staytuned]

I have had probably 30-40 random misfire CEL's this summer. I wouldn't worry a whole lot about it. As long as your not breaking up under WOT.

 

[psychlow]

Yeah - well, the other thing that worries me is that it acts like it wants to die after revving and I let off the throttle. I'd expect that if I were venting, but I'm recirculating.

I'm not getting CELs though... you can actually observe the miss at idle.

 

[Staytuned]

Ok thats a bit different then. I can barely notice that I am mis-firing at idle.

 

[paul s]

also check the coil pack..

 

[halligoo]

Mine did that with crappy gas. Threw in a bottle of octane booster and made it happy.

 

[LaN-]

my car wants to die after i rev it up past 2k, but i also have 2 bad rings and low compression.

I know you dont but it might help you out alittle

 

[psychlow]

Mine did that with crappy gas. Threw in a bottle of octane booster and made it happy.

Some of the gas in the tank is almost a year old, so this could be part of the issue. I think I'll pop my fuel line off the rail, run the tank dry and stick in new gas to see if that'll help.

also check the coil pack..

- Coil pack primary, secondary, and insulatory resistance was checked. Replaced with a known good unit anyway, and the problem still occurs.

I spent all last night replacing the TB shaft seals (what a PITA!) The old ones were hardened plastic dust instead of rubber. It feels much more solid now, so I'm gonna pop that back in and pray that it helps some.