Hi all,

Currently messing with my brother's 98 GSX. We are running an EVO 8 ecu with 9653 Rom. We have an issue where hitting 5k+ will start to breakup/miss. On or off boost, doesn't matter. I can vary the fuel from 11.1-12.4 with no change.

I have noticed one thing that helps, going lean. Running a 13+ AFR (E85) causes the break up to disappear. Obviously this is too lean to run normally, Is this simply the fuel overpowering the spark?

25PSI on an FP Green, aiming for 30PSI plus.

We have tried:
93 or E85
No Boost leaks
New plug wires,
New plugs (BR8ES @ .022)
New PTU
More timing,
Less timing
Less boost
More boost
Tested the Coil pack
Added Grounds
Changed Cam Sensor

Any ideas are appreciated. I don't have logs on this PC, however they don't show anything abnormal. TPS at WOT is 93%, 10.8% at idle. AFR and Injector cycle stays steady.

 

How much boost are you running? That is fairly cooler plug. Have you considered BPR8ES or BR7ES or even a tighter gap?

 

Will be changing to the 7ES soon to try that.

Currently 25psi, shooting for 30+ on an FP Green. I have somewhat ruled out spark blowout since you can free rev and get breakup.

 

Update: Ran BPR7ES @ .020, same issue prevails.

 

 

Keep us posted if you find the solution. Misfires can be a pain to diagnose. When did the issue start happening? Have you cleaned your fuel injectors? are you getting any timing errors? do you have an oscilloscope to check the exhaust cam sensor to see if its good?

 

Car was tuned on MAF, no issue. Car went down for full build/ SD tune, ran around semi-tuned for a few weeks, then this issue appeared when we tried tuning it for full boost. You can free rev and break up, so it's not boost. It's also not a hard miss, it doesn't feel like a wall, just sounds horrible and the car loses power, you can easily push through it.

Cam sensor has been replaced with known good. Fuel injectors are new. No CELs, timing checks out with a light.

 

Monday bump. Trying a new ECU today.

 

Bump for help, New OEM PTU and Coils did nothing. Wires did nothing.

Did not try the ECU yet.

 

Just so I don't leave this thread hanging.

We tried replacing almost everything electrical, fuel, or tune related with no change.

We ended up finding a broken valve spring on Cyl. 3.

Now to rip it apart again...

 

Damn man, that sucks. Best of luck!

 

Was it a stock valve spring that broke, or aftermarket?

 

Aftermarket, Brand new. I won't name the brand as they are looking into it for me. It's not a common occurrence however.

 

I see. Stuff happens, hopefully they make it right for you guys.