Weird 5k rpm stumble and knock with AEM F/IC

[legacylok]

oh electrical wizards of legacy central I have a problem that could really use your genius.

its a 5k stutter and knock on my ej20g with ej22t ecu and ignition with a aem f/ic here's what I know.

-doesnt happen when car is cold
-got worse when I went to colder plugs
-my tuner confident not a tuning issue
-switched coil packs out with no change
-fairly well grounded 2ga ground wires from block and chassis
-does it at same rpm whether full throttle half throttle or quarter throttle.
-developed a few months ago sometime after the f/ic was installed
-reset ecu with no change
-when I pulled plugs they all looked like they were supposed to
-occasional miss at idle
-when I log it air fuels seem to spike like the ecu is pulling fuel
-under 4000 rpm car drives and pulls great
-rewired the power and grounds to f/ic
-changed alternator



i feel like i have covered everything i can think of, and don't know what to do next

[Legacy777]

You mentioned knock in the title but didn't say anything about that? Are you seeing knock from the engine when this is occuring? It could be the knock system pulling timing.

I'd suggest going back to the stock heat range plugs unless you are seeing that they are overheating.

What boost are you running?

Are you using the stock crank pulley or an aftermarket lightweight one?

[legacylok]

I have a turbo xs knocklite hooked up to my stock knock sensor and at 5k the power stumbles and pulses then if I keep on the throttle the knock lite goes on and it feels like I hit fuel cut and the car starts to buck. it could be a knock sensor but it feels more severe then just pulling timing.

its currently at 12lbs but changing the boost didn't seem to effect it.

stock crank pulley

the other thing I noticed today is that when the car is cold it idles perfectly. when it warms up there is a random noticeable miss

[Legacy777]

You're right at the fuel cut pressure. Lower your boost to around 9-10 psi. Or have you done that already?

[legacylok]

I've tried that but I also have the map clamped at 3.8volts

[Legacy777]

Well I experience something similar to what you experienced with the perfect power. I was not altering the stock tuning at all, but would randomly get these massive loss of power on acceleration. It kind of felt like fuel cut.

I never really figured out what the problem was for sure. I thought it was added resistance on the crank/cam sensor wiring, but I was never able to confirm that.

I have my suspicion that the stock ECU does not like piggy back ECU's.