Lean Misfires at 2700-2800 rpm

[blusilvr]

i just had same issue, swapped ecu in and all is better now

[keithmac]

I had really crap part throttle miss-fire, changed the plugs and leads but that didn`t make a difference. My realtime o2 correction was pegged at 38% when it happened (max lean?). Pulled the ECU and replaced the capacitors, the difference is night and day! totally different car to drive and no missfires at all.

I don`t think you`d be able to tune though an ecu problem such as this with the SAFC because the values make no sense when the ecu goes tits up, plus the caps performance may change while driving if they`re on the way out.

Seriously pull the ecu and change out the caps, I`ve read a service life of between 7 and 10 years for the caps so even the newer cars may start to suffer from this problem?

[badass3000]

I have new caps

[DoctorDex]

I also have new caps.

I question whether or not the problem is ECU related. If it were ECU related, one would think that changing the % overclock would shift the misfiring rpm point up or down. I have tried different speeds of crystals and they have no effect on the Rpm point at which it misfires.

I'm also wondering if this issue of "spark blow out" on my rear bank is related. I've never had issues, to this degree, with spark blow out. At WOT, my rear o2 voltages are dropping to 0.60V between 4600-6000rpm and then they go back to 0.91V from 6000rpm - 8200rpm. Like I said before, it doesn't feel like spark blow out and the o2 voltages aren't bouncing around. However, I have noticed that my timing will start zig zagging a bit in the 4600-6000rpm range when it is blowing out. The strangest part about it all, is that if I do back to back runs, on one run it'll bounce between 0.89-0.91V and the next it drops all the way down to 0.60V.

Any ideas?

If I was to try swapping in an ECU from a 93 VR4 (with a 95 engine), would this mean that he is using a 95 ECU or a 93 ECU and would I have to make any changes to my car or his ECU, so it'll work with the CAS?

Thanks.

Declan

[LeMoN1438]

Originally Posted by DoctorDex

I'm also wondering if this issue of "spark blow out" on my rear bank is related. I've never had issues, to this degree, with spark blow out. At WOT, my rear o2 voltages are dropping to 0.60V between 4600-6000rpm and then they go back to 0.91V from 6000rpm - 8200rpm. Like I said before, it doesn't feel like spark blow out and the o2 voltages aren't bouncing around. However, I have noticed that my timing will start zig zagging a bit in the 4600-6000rpm range when it is blowing out. The strangest part about it all, is that if I do back to back runs, on one run it'll bounce between 0.89-0.91V and the next it drops all the way down to 0.60V.

Declan

I had a similar issue with the my front o2 going very lean at those rpm points, but I never dared pushing it above 6000rpms. My problem turned out to be the coils on the front bank.

[mehlosTT]

Just how lean or rich are those O2's when you think it's spark blow out? What are the AFRs exactly?
The 'bouncing timing you see, are you positive it is not just the ecu pulling timing when knock is coming on?
And what the heck is "TurboBob ecu"?
One of the first symptoms of an ECU (Mitsu uses) going south is the fueling...for what ever reason, a crappy ecu will often start to have problems controlling the fueling..then too lean..knock or like a bad O2 sensor run with leaded fuel, it starts to read rich so the ECU starts to lean her out terribly.
Best bet_ find a stock 1st gen ECU and try that.

[badass3000]

all these damn control moduals (ECU, ABS, SRS, AA, AE, ECS) are interconected. My crazy idle was caused by the ABS computer. Mabey try unhooking one at a time (or all at once) and see if it gets better.

[DoctorDex]

Originally Posted by LeMoN1438

I had a similar issue with the my front o2 going very lean at those rpm points, but I never dared pushing it above 6000rpms. My problem turned out to be the coils on the front bank.

Correct me if I'm wrong, but it seems odd that coils would cause problems solely on the front bank because each coil supplies spark to both a front and rear bank cylinder. If it was a bad coil, you'd think that you'd have problems on both the front and rear. Maybe your coils were just weak in general??

[DoctorDex]

Originally Posted by mehlosTT

Just how lean or rich are those O2's when you think it's spark blow out? What are the AFRs exactly?

Just before the blowout starts, my O2's are @ 0.91V and my AFR is @ 11.0. When the blowout starts my rear bank O2 voltage drops rapidly to 0.60V whereas the front bank voltage stays @ 0.91V. If I try throwing more fuel at the problem, the problem only gets worse.

Originally Posted by mehlosTT

The 'bouncing timing you see, are you positive it is not just the ecu pulling timing when knock is coming on?

I'm positive. I have a 1st gen, so I can see knock and there is no knock while the timing is jumping around/osciliatting +/- 1 or 2 degrees (during the blow out). The knock usually only comes on after a few seconds of rear bank readings of 0.60V and I suspect that it is because the blowout leaves a loaded cylinder.

Originally Posted by mehlosTT

And what the heck is "TurboBob ecu"?

A TurboBob ecu is an ECU that has been socketed (by TurboBob), so that it can accept different speeds of crystals. By using different speeds of crystals, you can "overclock" your ECU, which allows you to raise your redline limiter. I had this issue before I overclocked my ECU, so I can say with confidence that the overclock did not cause my problem.

[J-Ville VR-4]

Originally Posted by DoctorDex

Correct me if I'm wrong, but it seems odd that coils would cause problems solely on the front bank because each coil supplies spark to both a front and rear bank cylinder. If it was a bad coil, you'd think that you'd have problems on both the front and rear. Maybe your coils were just weak in general??

Maybe he just meant that they are physically mounted on the front bank? Because yeah, you are right in stating that each coil provides spark for cylinders on both banks.