smslyguy

i have a 01 z28 ss with 19,000 miles on it and get spark knock only under load and with warm temps over 75 degrees. any suggestions??? I have added additional mods to it since i bought the car, which are bbk s.t. forced air induction,air lid,k&n filter and still have spark knock.

mrmint69

Running lean or false knock from loud exhaust or leak. Low grade or bad fuel. Whats all been done to the car?

smslyguy

the car as headers, k &n air filter air lid forced air induction and low restrictive converters from slp. the spark know was still there before any of these were installed. doesnt matter what grade of fuel i run either.

smslyguy

what would be causing a lean mix?

Marc 85Z28

Clean the MAF with an approved MAF cleaner, run a can of Seafoam through it, then change your plugs.

mrmint69

Unmeasured air entering the engine. Maybe something is loose or disconnected.

smslyguy

i cleaned the maf sensor already no change. it only has 27,000 miles on it its done this since i have owned the car. I've ran injector cleaner through it as well. changed the crankshaft positioning sensor and still no change, however there is no check engine light on and no codes are stored.

smslyguy

i thought the knock sensors are supposed to prevent spark knock??

Z28luvr

Someone correct me if I'm wrong, but the knock sensor will detect a knock and the computer will adjust the timing accordingly.

johnny6

Yes thats what it does, i thought i had the same problem a couple of years ago and it turned out to be an exhaust leak.

AL SS590 M6

yes they are supposed to BUT carbon on the piston tops can cause a very light ping that can be missed by the sensors.
I had this problem with the 5.3 in my 03 GMC and Seafoam in the tank and thru the brake booster hose cured it.

Marc 85Z28

I didn't recommend the MAF cleaning alone. You really should Seafoam it and change the plugs. And when I say Seafoam, I'm not talking about cleaning the injectors.

smslyguy

ok i will try the seafoam but however i also notice a big reduction in power when the motor is "spark knocking" . When would lead me to beleive that it is a spark knock from the reduction of power.

SSpdDmon

I'm assuming you're seeing this with some type of scanner? If so, you're actually observing knock retard (KR). KR is the amount of timing pulled from the final timing figure commanded by the PCM. Becaue KR tends to be rather aggressive (for safety reasons), it'll pull more timing than it needs to in efforts to stop the KR. The amount it pulls is then slowly added back in assuming the knock sensors don't detect anything further.

Based on my experience, there's a spot or two in the factory spark curves for '01~'02 that are too aggressive. When I tune cars of those years, I pull the timing back in those regions a little. Oddly enough, the out-of-the-box tunes that come with some hand-held programmers do just the opposite. Are you using a Hypertech, Diablo, etc. hand-held programmer? Did the previous owner ever change the tune in the car?

Granted, the tune is only one possible source for your problem. Take note of what was said above. If after all of those suggestions you're still seeing KR, then it may mean your tune needs adjusting.

smslyguy

i have never tunned the car or had it tuned, i bought the car with 19,000 miles on it and it currently has 27,000. I dont know if the previous owner has had it tuned or not, but it has spark knocked sinse ive owned the vehicle. My buddy has a scanner which we hooked it up on and it was misfiring from cylinder to cylinder only under load, while it was spark knocking. It doesnt do this when the vehicle is cold though. Only when its up to operating temperature. I've been looking into tuners but im pretty confused to all the in depth reading you have to understand for them.