I know this is normally a forced induction system problem but my car has been having problems which I can only attribute to heat soak. After a bit of highway driving, if I down shift and accelerate to pass someone and floor it my car will get to about 5K and misfire or "cough" as some people have described it. Today I was doing my normal driving routine and floored it to merge into traffic and above 5.5K it started to knock and continued to do so after several tests. It did it in Phoenix and I just moved to Austin and it's doing it here. I verified it was the heat and not bad gas making it knock because I let it cool for a couple hours while I changed the belts this afternoon and floored it on the test drive and it didn't knock.

Anyone else have this problem? I have an 04 stock motor except plenum spacer. Ideas or suggestions would be appreciated.

 

What octane do you use?
Are your spark plugs relatively new?
How's your air filter?
Can your injectors be clogged? Low quality gasoline?
Try driving without the spacer and try to duplicate the problem.

 

I use 93 octane, my plugs were changed at 30K miles (currently at 52K), my filter has 5K miles on it and I just checked it and its still clean, I used an injector cleaner 3K miles ago and they were taken out and serviced in the 30K mile maintenence(whatever the hell that means). I was thinking about the low quality gas but that would mean it should have knocked again on the test ride after I changed my belts. I'll try driving without the spacer but only after I've exhausted all the other options and by then I'll just take it into the dealer. Thanks for the quick replys. Keep em coming.

 

replace plugs....go with iridium....what other mods do u have??
make sure u dont have a coolant leak....even a small pinhole can affect a lot of engine temps...radiator still in decent condition?? go with a low temp t-stat and koyo radiator if all else fails....

 

Cool, I'll try replacing the plugs. As for other mods all my money went into suspension, brakes, and tires for the track. Engine is completely stock except for the plenum spacer. Pretty sure I don't have a coolant leak, I keep my engine bay so clean you can eat off of it and I'd notice one. Would heat wrapping the headers help or venting the engine bay?

 

just on a hunch i reset the ECU and that seems to have fixed it. Hasn't knocked yet in 2 days.