Misfire from 2800 to 4200 RPM, ECU Problem?

[All_talk]

This is a strange one that has been plaguing me for years. I’m get a misfire at heavy load on one or more cylinders as I come across about 2800 rpm thru 4200 rpm, above that it pulls strong and smooth to redline. It always seems to be there to some extent, sometimes barely there with just a slight power loss, sometimes its really severe with hard bucking. At light to moderate load (up to about 3-4psi) there is no problem and the power is smooth, but the deeper I get in the throttle the worse it gets. Its worse in the lower gears when the RPMs come up quick, doesn’t really do it at all with a 5th gear pull. It did it with my stock EJ22T and now does it with my JDM EJ20G swap. About the only parts that have been constant all this time are the ECU, MAF sensor and maybe the IAC valve, every thing else has been change at one point or another. Its more severe with higher boost but still happens on the stock boost control. I have even run it with the waste gate running straight off compressor outlet.

My first thought was fuel, but the AFRs are good and the fuel pressure checks out. Now I’m leaning more toward ignition, maybe something with the advance in that part of the map. By watching my AFR gauge I have learned that the stock ECU switches to open loop at 4200rpm regardless of load or manifold pressure, I believe this is normal and intended. But the fact that the misfire clears at this same point make me think it might be the ECU itself.

I’ve been driving around this problem for far to long, I just avoid full (or near full) throttle until I get above 4200 and the rpm fall back from redline keeps me out of this range when I’m ‘getting after it”, but I sure would like a fix. Anyone had a similar issue? Thoughts?

Gary

[Legacy777]

Hi Gary,

You mention you've replaced "most" of the parts between engine swaps. What of the ignition system was reused?

What about wiring, did you check the harness to make sure everything is good there?

What ECU are you running?

What plugs & gap are you running?

You running coil pack or coil on plug? If coil pack, how old are your wires?

Any more details would help.

[All_talk]

The only thing in the ignition system that has not been changed at least once is the harness in the car (and ECU). igniter, coil, wires and plugs have all been changed. Not all of these parts we new, the igniter and coil were swapped with know good unit from my wife’s ’97 OBS (my old parts run fine on her car).

I have not tested the resistance of each circuit in the harness but no general problems, no wired cut, connectors are clean.

ECU is the stock EJ22T

Stock plugs for the EJ22T, stock gap

Coil pack, wires have been changed.

More detail…

I get no CELs, the only CEL the car has ever thrown in 163,000 miles I have driven it is a knock sensor after I did the head gaskets on the EJ20G about 12,000 miles ago because I kinked and broke the old brittle wire. Fixed the same day and no trouble since. I have reset the ECU over and over with no change. It is currently running on the stock 370 pink injectors at stock boost. But it showed the same problem with the 440 grey tops, EFCD and manual boost control, the higher I set the boost the worse it gets.

Gary

[Legacy777]

Well, process of elimination. I would check the resistance on the engine harness to the ECU next. If that comes back good, maybe look at another ECU to see if that works.