Misfire at high RPMs
My car has been misfiring at higher RPMs recently, starting around 6000rpms or so, and seems more prominent in higher gears (not noticeable in 1st and rarely in 2nd). I also noticed that this seems to coincide with a significant drop in oil pressure on my stock '90 gauge. I'm curious how the 2 could be related. I know the gauges aren't known for their accuracy and it doesn't seem like a misfire would be a symptom of an oil pump failure (maybe I'm wrong). I'm wondering if it's possibly something electrical?
This is on my turbo'd '90 with a '95 motor, MSPNP. Things I've done since the problem emerged: replaced fuel pump changed the fuel filter changed plugs regapped plugs pulled timing leaned out and richened fuel curve installed a larger battery pulled and reseated injectors added coil on plugs flashed firmware on megasquirt and loaded basemap checked as many grounds as I can find removed the wastegate actuator so it runs NA adjusted the boost from the wastegate (~8psi) to 15psi pulled the motor to install rods, shaved head and new headgasket. The problem continues after each thing has been changed, nothing affected the miss at all. I figured I'd post up, see if anyone had any ideas or suggestions. I'm kinda running out of things to try. I'll go out and datalog it to post up in a few min. |
What plug gap are you running?
--Alex |
Originally Posted by pdexta
(Post 561820)
I also noticed that this seems to coincide with a significant drop in oil pressure on my stock '90 gauge. I'm curious how the 2 could be related.
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Originally Posted by magnamx-5
(Post 561825)
Well a drop in OP suggests detonation to me detonation would be more prominent under greater laod and higher gears.
Referring to the early NA's OP acting in a det detection gauge. You're *probably* not actually loosing pressure, the gauge just flutters when knock occurs. --Alex |
Originally Posted by magnamx-5
(Post 561825)
Well a drop in OP suggests detonation to me detonation would be more prominent under greater laod and higher gears.
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2 Attachment(s)
Current msq and datalog attached.
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Originally Posted by AlexO35
(Post 561821)
What plug gap are you running?
--Alex |
Currently running the plugs gapped at .034, I've had them as low as .024 and it didn't help. Also, the problem was happening before and after COPS.
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I didn't see the word "alternator" anywhere in this thread. could be a weak point as well.
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Originally Posted by y8s
(Post 562121)
I didn't see the word "alternator" anywhere in this thread. could be a weak point as well.
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2 Attachment(s)
Thanks for the advise. I put a new alternator on this morning, but it's still doing the same thing. I really appreciate the suggestion though. I think you guys may be onto something with the voltage drop, I went through some older logs and didn't see that same kind of drop.
Attachment 198202 Attachment 198203 If anyone thinks of something else to try, please throw it out there. |
One of the times I had such symptoms; one of them it was the VAF and the other one a bad distributor.
IMO the alt swap is a waste of money and time, but of course I could be totally wrong. |
Originally Posted by mazpr
(Post 562183)
One of the times I had such symptoms; one of them it was the VAF and the other one a bad distributor.
IMO the alt swap is a waste of money and time, but of course I could be totally wrong. I had an extra alternator already so there wasn't any cost and after all the things I've already tried, I was more than willing to spend 30 minutes swapping it out to see if it helped. |
Originally Posted by mazpr
(Post 562183)
One of the times I had such symptoms; one of them it was the VAF and the other one a bad distributor.
IMO the alt swap is a waste of money and time, but of course I could be totally wrong. I had an extra alternator already so there wasn't any cost and after all the things I've already tried, I was more than willing to spend 30 minutes swapping it out to see if it helped. |
run a ground from the battery to the botom of the alternator that cured my voltage drop just fine. if it works maybe voltage drop was causing your coils to not have enough juice.
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Ran the ground to the alternator and it is still doing the same thing, thanks for the suggestion though.
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maybe try running less than 10:1 AFR in boost?
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What sort of coils are you running? You may need an upgrade.
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looks like he went to toyota coil on plugs.
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