MYBLKSS

iTrader: (1)

I was A-taping the car over the weekend and noticed that I was picking up about 3*'s of knock at WOT. What would cause this?

horist

There are two sensors in the top of your motor, they are knock sensors (they screw into the lifter valley cover under the intake manifold)

They're like microphones, they detect vibrations occurring at certain frequencies, frequencies that often mean uncontrolled burns aka detonation/pre-ignition.

Basically the knock sensors report this noise back to the PCM and the PCM then will pull timing advance in an attempt to stop the knocking. It's a safety feature to protect your motor.

so w/3* of knock retard you're loosing 3+ degrees of total timing advance.

MYBLKSS

iTrader: (1)

In A-tap i was monitoring advance on #1 cylinder. Is advance always a negative value?

MYBLKSS

iTrader: (1)

Could this be caused by bad Gas. I have been buying gas from one of the smaller gas stations in town and I think it may not be as high of a quality (octane) than the Larger stations.

foff667

iTrader: (2)

it could be alot of things...bad gas, actual knock maybe not audible to you, a noise near the engine that the sensors pick up as knock...thats why lt1 guys go to the lt4 knock sensors cuz they are less sensitive...i think the turbo buick sensors are even less sensitive...not sure what would work on our cars...but some people also say that the pcv system causes oil buildup in the intake...or the egr system might cause it who knows...a million things that could cause it means a million things to check...as long as your not getting like 5-6 degrees and you cant hear it its probably false knock...probably.

lata
Bill

horist

yes in atap I believe if you monitor advance on Cylinder 1 it will always show negative, there's another option of just ignition advance or something like that that will show the same value but positive.

it could be bad gas if it's real knock... or it could be false knock from your mods (anything rattling, y-pipes banging, etc..)

JeremyF

iTrader: (23)

The PCM limits the amount of timing pulled @ WOT to 4deg so therefore you will not see a value of 5-6. I stated in a prior post that the amount of timing pulled does not reflect the severity of the spark knock. If there is extended retard throughout a gear never returning to full timing then BE WORRIED. But this is a little piece of info I thought that should be shared.

Jeremy