I need some advice on knock retard. my car is getting anywhere from 2-7 degrees of knock retard almost all the time. At a 65 mile per hour cruise im getting 5 degrees of knock. Even under the lightest acclereation a at low speed i get 3-5 degrees. If i get on it, i get 7 degrees and it slowly comes back down to 5 degrees. I sent a datalog to bryan at pcm for less and he said I have a problem with knock sensor. So i replaced the sensor and the pig tail. If anything it has seemed to get worse. I dont know where to go next. I dont have any exaust rattles, but my rockers are loud. I am running the comp o.e lifters at 1/4 turn preload. I dont know what to do next. I could live with a little knock, but i think this is excessive. I have a feeling that my tune probably limits to my knock to a max of 7 degrees. If it was allowed to the computer wold probably pull even more timing. ant help would be appreciated. If someone would like to look at a log i could go make one.



Thanks in advance,

Scott

 

Do you have a LT4 knock modual? If not get one and try it.

 

yeah i have one installed now. I going to install standard lt1 km tomarrow to see if there is any difference.

 

Have you ran the car with some unleaded race gas to see if it is false knock?

 

Take a real close look at your header clearance on the driver side and consider the age / stiffness of your motor mounts. Oftentimes, when the motor torques over under load that header will hit the motor mount housing or crossmember. Just went through this on mine...I had 3/4" of clearance and could rev it in the garage while watcing and it wouldn't even come close to touching. Under load though was a whole different story...even with brand new poly mounts. Even light throttle can torque the motor over farther than you'd think...it's trying to move a 3600+ lb. car.

If that's not the problem, check for vacuum leaks. Most common culprits are the pcv hoses, intake elbow, throttle body gasket, and sometimes the intake itself. The best way to check the hoses is to physically remove them and inspect on the bench. For some sick reason the cracks tend to form on the bottom. Another method is to spray carb cleaner on suspect areas while the motor is running and listening for any change in the idle. Hard to find leaks on the bottom of hoses this way though and also easy to start a fire if you're not careful.

If all that checks out, look for exhaust leaks and maybe go another 1/4 to 1/2 turn on the rockers and see if it changes anything.

It can be a real pain to sort out and unfortunately it's quite common. I feel your pain...I'm going through the same thing right now. Was getting audible knock which went away by pulling some timing but am still getting false knock from somewhere. Just finished pulling the header and grinding the d.s. motor mount down for more clearance. Crossing fingers that takes care of it in my case...we'll see.

 

Are you sure you have the correct knock sensor? Did you get the one for the 96/97's, with ~100,000 ohms resistance? Did you check the resistance from the single pin on the sensor to the block, harness wire off? Did you verify you have 5V between the single wire in the harness connector and the block, with the connector off the sensor?

What fuel are you running, and what is the elevation where you live?

 

I got mine tuned out maybe not the safest but OH WELL

 

Thanks for the replies guys. I'll double check the driver side header, it is closer than i would like, but didnt see rub marks, but i'll look again. Injuneer, I have replaced the knock sensor with the 100kohms sensor from gm. i have physically resistance checked the sensor but not the harness for 5 vdc. I will check that tonight. My elevation is 3300 feet and i run 91 octane fuel, which is the highest i can buy at the pump. Ive sprayed the intake down with carb cleaner and did not notice any change in running or smell through the exaust. So if i have an intake leak, it would have to be down through the bottom of the intake in lifter valley. I dont know if this common or not. If you guys have any other ideas, let me know i will check them also. thanks again.