At COTA on lap one, my perfectly good EVO IX RS decided to start caughing, burping, and flubbering just as boost was coming on? Boost leak right.....wrong. Nope. Pulled spark plug and the one we pulled was broke. Gapped and replaced all with new plugs. Same problem persisted when getting on boost. My day at COTA was done. Car idles and starts fine. Accellerates fine off boost. Got hom 2 days later and tested gas. It was e92....not e85. Ahhh, I must have put in e100 by mistake at pump before putting car on trailer. Sure enough, drained gas and car runs like it should with correct e85 fuel. Did this for 2 test rides on different days and the car was perfect again! Problem solved right? Wrong. Nope. Car acted up again tonight and it's doing that same thing on boost again where it cuts out and flubbers and flashed the yellow engine light.

I am stumped. Anyone? No leak under boost leak test.

 

Sounds like your car was flashed with the Tephra mod that upon engine knock will flash fast or slow depending on knock counts. I suspect you maybe having fueling issues under boost. Do you have an afr gauge installed?

 

It could also be a failsafe in the tephramod kicking in, but I would check your fuel cut tables as that is what is sounds like to me, most likely your tables were tuned in the summer, and now that it is cooler you are hitting the fuel cut, especially at the low end of the RPM.

George

 

Thanks guys. All 3 replies will be followed up on. Appreciate your time in responding. We are thinkking similar things.

 

Broken spark plug. Uhm was the parts missing?
Compression test is mandatory.
If compression is with in spec ok.
If not cylinder leak down is in order.

 

Last thing remember with different versions of the Tephra ROM the load that activates fuel cut is different, the USDM ROM follows 2-byte load which is considerably less than your 1 byte load you are most likely logging. The two byte load will change with temp and humidity whereas the one byte does not. Be sure to log two byte load when setting your boost limits, boost tables, and fuel cut.

George