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ECUflash Breaking up @ 5K +, scratching my head. Lean bandaid?

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I'm not as knowledgeable as you but I have a suggestion. Have you checked the alternator under load? My understanding is that DSM shuts off alternator at WOT however with evo ECU it will stay on and if not putting out the required juice at higher RPM it could be an issue.

That is more of an obscure idea I guess but once time I had this alternator that put out too much voltage and I then realized that a faulty alternator can look more than one way.

I did check this, if you look a few posts up, I had the same idea LOL. Makes sense. But voltage was fine ~13.5

Have you tried removing the ignition capacitor from the ignition coil/PTU power feed circuit?

I have not. Not even sure if it’s there honestly. Your talking the little silver capacitor on the intake mani right?
 
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Found multiple posts that state it is just there to filter electrical noise from the radio.

Then I found one single post, that is having the same issue I am, due to this capacitor.

I will check it and update.
 
Yes....
It dampens the primary ignition circuit from the coil firing events.
Component "F"
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It filters out radio interference caused by the coils firing not interference caused by the radio.
 
Update: Found wires leading to coil connector had split under the loom, someone had tied in an aftermarket tach at some point.

Replaced wire, no change.

Ordered new harness.
 
To follow up, we had a Kiggly Street Steel spring crack and break with break in miles on the car. I have reached out to Kiggly for their opinion.

Valve is bent, Head is unknown (haven't pulled yet, just bore-scope). Valve guide is probably cracked, piston is ok.

Lucky it fell in the stroke where it did, it could have been way worse. Odd thing is we never heard any noise, and the valve got pushed back up into it's seat enough to pass a compression test. This had to have happened on first start or initial drive, as we always had this issue when tuning.

So the reason going really lean helped, it was an intake valve, so basically I was flooding the cylinder since it couldn't pull in enough air (which is what I thought the problem was on a larger scale).
 
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