Detonation (CEL flashing)

[turbo84voyager]

Hi everyone,

I am having a knock problem with my 2.5 g-head. I finished tunning my cal a few months ago and it runs great, I blew a exhaust manifold gasket so I pulled it all apart and replaced the gasket. Now everything is back together and I have been getting the CEL knock light flashing occassionially. Sometimes It will come on at 4 psi sometime at 10, and sometimes never. Other than replacing the gasket the only thing I changed was the oil which I switched over to full synthetic Valvoline. I did fill the tank up right after I put it together. I must have tightened the adjustable wastegate a little tighter when I put it together because I had about 2 psi more boost. My EGT's and wideband are all in range and my plugs look fine. I pulled 2 degrees of timing and added 2% more fuel to the cal and I took it for a ride, the light did not come on. Then it started flickering again. I cannot hear any knock. I am stumped as to what could have caused this problem. I thought it was bad gas so I fulled up with gas from another place and it is still there. I guess it is possible more than one place has bad gas. Could it have something to do with the synthetic oil? I have not taken notice of it using any oil. The engine has wiseco pistions. Any advice would be appreceiated.

Thanks,
Justin

[badandy]

With the random-ness of the issue I would suspect the sensor itself. Do you have any race gas available in your area?...if so I would run some and see if your light still comes on...or swap it out for known good sensor (don't assume a new sensor is good!).

I'm wondering if you have an over active sensor picking up engine noise as knock. Do you have all fasteners tight? I ask only because one time my power steering bracket had a bolt fall out and that part of the bracket vibrated against the block which set off the knock sensor.

Are you running your crankcase evacuation into your intake like the stock PCV setup? it's possible you are contaminating your combustion with blowby and lowering the octane of the mixture.

just some things to check/contemplate

[turbo84voyager]

I am going to check over for loose bolts. I do have rattle in the exhaust. Mabe it is picking up that. It is a standard ignition sensor and it is only about 1 year old. I always wondered if it is a very sensitive sensor because it will do this when my a/c compressor cycles and almost no load on the engine. I am doubting it is a timing issue because I am running about 9 degrees less total timing than the original 2.5 g-head cal I started with. I dont have a crankcase canister, I didnt take notice of blow-by. There is only 4K on the motor.

Justin

[badandy]

I am going to check over for loose bolts. I do have rattle in the exhaust. Mabe it is picking up that. It is a standard ignition sensor and it is only about 1 year old. I always wondered if it is a very sensitive sensor because it will do this when my a/c compressor cycles and almost no load on the engine. I am doubting it is a timing issue because I am running about 9 degrees less total timing than the original 2.5 g-head cal I started with. I dont have a crankcase canister, I didnt take notice of blow-by. There is only 4K on the motor.

Justin

There is your answer right there! You have an overzealous knock sensor my friend. if it picks up your a/c compressor clutch that it DEFINATELY is your problem.