Long time lurker, was hoping to get a little help troubleshooting a new problem I've had. A couple of months ago I had my stock clutch changed out for an ACT HD clutch at a local Mitsubishi dealership. New clutch feels fine, but since then whenever I go WOT my engine seems to hesitate in all of the gears in the upper RPM range starting at around 6000-6500 rpms. It feels like my acceleration all of a sudden hits a plateau and it just flatlines. No engine/fuel cut, no clutch slipping like before, no unusual noises. To troubleshoot the problem I've tried the following:

1. Boost leak test - found a couple of loose band clamps and tightened them down with no resolution

2. Swapped out coil plugs/wires/spark plugs with no resolution. Current plugs show no signs of lean mixtures

3. Swapped out cam angle sensor with no resolution

4. Ran 2 full tanks of Chevron gas (thought it might have been bad gas) and even tried some Techron fuel system cleaner

5. Multiple logged runs with the Autronic ECU and Boost, EGT, A/F gauges with no visible differences. Same map as before. No low boost, no high temps, no lean spots. Intake, coolant, charge temps have been fine. Battery voltage have been 13.6-13.7. Mean injector duty cycles have been fine.

BTW the car is an '03 Evo, about 71,000 miles, Autronic stand alone ECU with bolt-ons (intake, upper and lower IC pipes, intercooler, ported ex manifold, 02 housing, DP, exhaust), cam gears, and 272 camshafts. Car had been fully tuned and was running great prior to the clutch change. Car still idles and runs the same except when going WOT above ~6K rpms. I'm not even sure that the hesitation is directly related to the clutch change, maybe it's just coincidental. It almost feels like the car is pulling ignition timing in the high rpms, I just can't quite explain it. Any ideas would be appreciated.

 

Any thoughts?

 

what plugs and gap?

 

Bpr8es, 0.025

 

How did you break it in? Is it a unsprung clutch?

 

Broke it in with easy street driving for ~700 miles, no launches or quick shifts. Actually still haven't launched the car since the clutch change, just more aggressive shifting, which feels fine. Swapped the stock for an ACT MB7-HDSS, sprung clutch. Prior to the swap the clutch was definitely slipping, losing engagement mid pull with RPMs spiking up. This feels totally different. Feels like the engine falls flat on its face around 6000-6500 rpm.

 

How's the air cleaner? Do you sill have stock cat? Does it blow any smoke?

 

are you getting 100% throttle opening?

 

K&N cone filter that I just cleaned last week. No, have a 100 cell race cat mated to a Buschur exhaust. Now that you mention it, I used to blow a little puff of black smoke whenever I went WOT, which I don't seem to do anymore. Wonder if the cat is directional and they reinstalled it backwards. Yep, 100% throttle opening on the autronic logs.

 

turbo might be taking a ****, turbo making any sounds?

 

Nope, no new sounds that I can hear. Turbo seals at least seemed good on the boost leak test. Boost also hasn't changed and holds steady up til 6-6.5k when it starts hesitating.

 

Well, it's not my cat, changed it out and still have the same hesitation. Doubt they even touched the exhaust. Even tightened up my APS BOV thinking it might be leaking from being old, no change. Found a loose ground on top of the tranny that I tightened up, but again, no change. Checked to make sure I still had the same map in there and sure enough, it's the same one as the last time I got tuned. Any other thoughts?