My car is bucking a lot under boost around 5/6k revs in 3rd 4/5k in 4th and so on.
I have changed the spark plugs which did slightly alleviate the problem but for the most its still there.

I'm guessing the coil parks need replacing. If this is the case s are stock coils/ignition system good enough to cope with 28 psi with E85 or should i look to go aftermarket? Also any suggestions?

During the day when its warmer it isnt as much as a problem but on cold nights is when its at its worse.

Car has been running fine for a year without any change to any parts

 

I had the same problem and come to find out my coil packs was not connecting to the spark plug well an was leaving carbon tracks. It started right after I changed my plugs. But if you are running stock packs then I would imagine they are getting weak. I would recommend spoolin up coil packs. Good price with a 3 year warranty.

 

Stock coils are fine to 600whp or so. Yours are probably tired. Some last a long time, some don't. Mine started crapping out after about 1500 miles of having the FP red on. I just found some good used OEM coils from a local guy and I've been good since..

 

yeah im not sure if they have ever been replaced on my car. It has 170000kms on it atm so it is probs time to replace them. it did get gradually worse.

 

When is the last time you performed one of these?

https://www.evolutionm.net/forums/ev...g-how-why.html

 

I would of suspected a leak but it gets worse at night when the air is cooler during the day its no where near as bad.

Going to get my coils look at today

 

Nevertheless, a pressure test should be the first thing you do. Many times over the 11 years I've been here has odd behavior been traced to a leak, and quite a few persons here have pressure leaks and don't realize it.

Just FYI

 

have you checked if your cruising timing chart is still good.

 

you wouldn't check cruising timing if the car is missing on boost...

 

My first guess would be cool packs but it could also be a fuel issue. Keep an eye on you FP