misfire under boost
06-13-05, 05:09 PM
#1
misfire under boost
how can I figure out wtf is going on here... just started happening, the car will misfire under boost BADLY, mostly at higher RPM.
seems to happen when not under boost too at super-high RPM, but this might be a different issue,.
seems to happen when not under boost too at super-high RPM, but this might be a different issue,.
06-13-05, 11:07 PM
#5
XBL** Ownicus
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I'd take Icemark's advice into consideration. I'd do a full tune-up if you haven't in awhile first and go from there (these cars always love the maintenance anyways). 
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06-16-05, 11:12 PM
#9
plugs and wires are A-OK!
Checked the TPS, it seems to be OK.... kinda weird though, with the car running the S-AFC reads the TPS % as fluctuating between 98 and 100% instead of staying at 100% with the car at WOT.
the misfire is REALLY bad now, seems to be getting worse... the car basically hits a wall, backfires, etc..... and it does it now after 2-3 seconds on the throttle TOPS above 3500 RPM... don't think it does it below that but I'm not sure. I don't think that I can get the car to rev to 7k in gear, certainly not to 8k.
I'm running an FD pump that I've /never/ liked, wondering if maybe it's going bad on me. (again).
Is a TII pump enough to fuel 550 primaries and 720 secondaries at 5PSI boost? (super ported wastegate, s5 turbo, no boost controller till I figure ALL the issues out)
Checked the TPS, it seems to be OK.... kinda weird though, with the car running the S-AFC reads the TPS % as fluctuating between 98 and 100% instead of staying at 100% with the car at WOT.
the misfire is REALLY bad now, seems to be getting worse... the car basically hits a wall, backfires, etc..... and it does it now after 2-3 seconds on the throttle TOPS above 3500 RPM... don't think it does it below that but I'm not sure. I don't think that I can get the car to rev to 7k in gear, certainly not to 8k.
I'm running an FD pump that I've /never/ liked, wondering if maybe it's going bad on me. (again).
Is a TII pump enough to fuel 550 primaries and 720 secondaries at 5PSI boost? (super ported wastegate, s5 turbo, no boost controller till I figure ALL the issues out)
06-18-05, 05:28 PM
#12
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I had the same problem, ran fine when cold but when warm misfired like a MF! it ended up i had a small slit about half an inch in my innercooler piping. check it out drove me nuts. boost leak = missfire good luck
06-19-05, 12:08 PM
#14
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no, same result weather engine cold or warm (well, I think, don't think I've touched wot/boost when it's COLD).....
few days ago, ambient was in the 90's with 100% humidity and it did it, last night in the 50's and dry, did it too....
posting from friends computer...... this is Terrh
few days ago, ambient was in the 90's with 100% humidity and it did it, last night in the 50's and dry, did it too....
posting from friends computer...... this is Terrh
06-19-05, 12:26 PM
#15
i think you missed something during your inspections:
1) spark plugs are fouling/fouled
2) plug wires have a pinhole or cracking, carbon trailing the coils
3) spark plugs are carbon tracking and arcing to the block rather than the electrode
4) coil towers cracked and leaking spark
5) IC piping has a hole or crack in it
6) FCD is set improperly
these are the basics and most likely problems
1) spark plugs are fouling/fouled
2) plug wires have a pinhole or cracking, carbon trailing the coils
3) spark plugs are carbon tracking and arcing to the block rather than the electrode
4) coil towers cracked and leaking spark
5) IC piping has a hole or crack in it
6) FCD is set improperly
these are the basics and most likely problems
06-20-05, 10:51 AM
#16
plugs are clean, no excessive carbon
plug wires are new. and not causing a problem, I swapped to the old set and the same issue.
no vacuum leaks at ALL, I'm so proud lol
FCD is not in the car, only running 5psi right now
just for kicks, I swapped to a TII fuel pump that I had, same issue. Going to get a new fuel filter tomorrow (haveta order them in! which sucks), I'm almost conviced that the car is not getting enough fuel when this happens.
plug wires are new. and not causing a problem, I swapped to the old set and the same issue.
no vacuum leaks at ALL, I'm so proud lol
FCD is not in the car, only running 5psi right now
just for kicks, I swapped to a TII fuel pump that I had, same issue. Going to get a new fuel filter tomorrow (haveta order them in! which sucks), I'm almost conviced that the car is not getting enough fuel when this happens.
06-20-05, 11:43 AM
#18
same was happening to my car... I couldn't figure it out after like months and months of trouble shooting and replacing stuff... and now I'm installing a megasquirt EMS because I was tired of dealing with it 
(also taking out most of my usless crap at the same time, hopefully it'll fix itself)
(also taking out most of my usless crap at the same time, hopefully it'll fix itself)
06-21-05, 09:48 PM
#20
changed fuel filter. Seemed to improve it but not really much. Oh well, was due anyways with 80k miles on the car now. Swapped fuel pumps (put in an FD pump). Same thing exactly.
Changed leading coil. Same thing exactly. Don't think it's the trailing coil, cos it does the same thing with the trailing coil unplugged.
Pulled the TPS connector (started to get wacky I guess lol). Same problem still.
Put it back on.
Pulled the plug wires, looked iffy even though I just bought them last year. Changed them. Same deal.
The car will rev cleanly to 7500+ in neutral and in gear at LIGHT THROTTLE.
the car will NOT rev cleanly past about 6K in neutral at WOT.
the car will break up/misfire/etc (it actually just sounds ... weird, steady, but weird) at WOT in gear from about 4000RPM and up at WOT. if I stay in it while it's misfiring it will clear up and work for 2-3 seconds before misfiring again, etc, etc...
what the hell do I do now?
Changed leading coil. Same thing exactly. Don't think it's the trailing coil, cos it does the same thing with the trailing coil unplugged.
Pulled the TPS connector (started to get wacky I guess lol). Same problem still.
Put it back on.
Pulled the plug wires, looked iffy even though I just bought them last year. Changed them. Same deal.
The car will rev cleanly to 7500+ in neutral and in gear at LIGHT THROTTLE.
the car will NOT rev cleanly past about 6K in neutral at WOT.
the car will break up/misfire/etc (it actually just sounds ... weird, steady, but weird) at WOT in gear from about 4000RPM and up at WOT. if I stay in it while it's misfiring it will clear up and work for 2-3 seconds before misfiring again, etc, etc...
what the hell do I do now?
06-21-05, 09:50 PM
#21
not sure if this is related or not. sometimes there is a vibration when revving, it's NOT drivetrain related.
And my gauges/logicon/backup lights/idiot lights don't work either, they keep blowing the fuse, but that's a whole nother thread.
And my gauges/logicon/backup lights/idiot lights don't work either, they keep blowing the fuse, but that's a whole nother thread.
06-26-05, 01:23 AM
#24
W. TX chirpin Monkey
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Check the ground in the exhaust, I accidentally removed mine doing a catback swap, and the O2 sensor would read really irregular...caused it to sometimes hit a wall at 4k, other times nothing, and others serious ignition break ups. I would seriously add another ground to your exhaust. The stock one is a thin wire on the drivers side muffler.
06-26-05, 01:37 AM
#25
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check your voltage to your fuel pump and check your fule pressure i bought a brand new walbro 255 and it was bad wright out of the box mad my car missfire horably. you can buy a cheap fuel pressure tester at shucks auto zone etc.