ghost knock problem, need help

[mr2cam]

Hey guys, we finally got our truck up to the dyno to have our tuner work on it and we ran into an issue with it pulling serious timing due to knock, at the time we had 87 octane in it which we thought would be fine for 10:1 compression, well we came home and filled it with 92 and it still seems to be pulling timing, well tonight I put about 5 gallons of 110 mixed with 3 gallons of 92 in it and still the same thing.

Here is my question, our truck is a 408 and has brand new Delphi knock sensors, but the wiring harness is from the old junkyard 6.0. Has anyone had issues with that wiring harness causing ghost knock?

[pl4yboy]

What headers, are they hitting anything, are you positive the header bolts are tight?

[mr2cam]

American Racing 1 & 7/8ths stainless steal headers, bolts are tight and no they aren't hitting anything.

[pl4yboy]

Knock sensors may be bad.

[mr2cam]

Hmm, well they are brand new, I talked to a GM tech and he said the sub harness on the knock sensors get replaced a lot, were gonna start there and see what happens.

[pl4yboy]

True story. Check it out.

[RedHeartbeat]

and if that doesn't fix it you may need to lower the sensitivity of the knock sensors in the tune.

[mr2cam]

and if that doesn't fix it you may need to lower the sensitivity of the knock sensors in the tune.

He did that actually and we picked up like 80rwhp just from that, he said it was still dropping the timing down to about 8 degrees under load due to knock.

[farmtruc]

I've seen the engine harness shorted before. This causes knock. Replace the knock sensor harness first.
There r tables u can edit to limit timing and knock, but that's not going to fix the issue. It will just limit the amount of knock and how low timing can go.
When I run into this I try another calibration and PCM. If there's nothing wrong with the truck mechanically, it'll fix it


Good luck.

[remauto1187]

He did that actually and we picked up like 80rwhp just from that, he said it was still dropping the timing down to about 8 degrees under load due to knock.

Your ghost knocks might be coming from your pistons. I remember reading about somewhere. Forged pistons can cause the ghost knocks. Are our spark plugs showing any sign of actual preignition?