4AGZE misfiring issue

[mr2gze]

Ok so my AE86 with AE101 4AGZE conversion is misfiring somewhere between 5500-6000 rpm. I completed the conversion 5 years ago, and the car has been running fault free ever since. The engine is as per factory apart from a small front mount intercooler, and made a healthy 150ish rwhp a year ago.

So here's the problem... It will rev perfectly normal up until the misfire, at which point it feels like a rev limiter, and seems to breaking down across all 4 cylinders. If I hold the throttle at say 75%, it will rev past the point and through to redline, but I can still feel a very faint misfire. The problem randomly appeared when I was driving home from work a couple of months ago.

What I've tried:
- Replaced plugs and gapped to .8
- Replaced Leads and Coils (with used items...)
- Noticed 3/7 ECU capacitors were leaking, so replaced the ECU with a AE92 4AGZE ECU

The replacing and gapping down of the plugs caused the misfire to occur higher in the rpm range (from 4500 rpm to 5500 rpm), otherwise the problem remains as per before.

I'm starting to think something fuel related...

Thoughts?

[allencr]

Code/s? ?

[mr2gze]

Code/s? ?

Before I replaced the ECU it had codes:
21 - Oxygen Sensor.
25 - Air-Fuel Ratio Lean.

I have never run an 02 sensor.... and I assume 25 is related to 21...

[feral4mr2]

have you pulled the plugs since changing them to see if one is fouling more than others, or running leaner?

[mr2gze]

have you pulled the plugs since changing them to see if one is fouling more than others, or running leaner?

Hi mate, nope not yet. Will pull them tomorrow and have a look.... Cheers.

Keen to hear any other suggestions? Getting desperate.