Sweet. So let's start at the beginning. I got a 200 Trans Am about 3 years ago. It's an auto so it had 2.73 gears. At 80MPH (4th gear at 2000RPM) I noticed it would resonate on the deceleration. Just some vibration I could feel. (it was like woom-woom-woom).

Fast forward. Broke a rear end, added some go fast. I added poly motor mounts and a poly trans mount. Now at about 60MPH (4th gear, 2000RPM) it starts the 'woom-woom-woom' and now it's severe enough to cause the SES light to flash.

I recently put in a 3600 stall and SFI flexplate and a new real main seal. I figured the flexplate would help the issue since it SEEMS to be RPM related but it ONLY happens in 4th at 2000RPM. No other gear.

Well it didn't do junk. Except now when it detects knock, my torque converter unlocks and it hits like 3000RPM to cruise.

My proposed remedy since I do not have HPTuners (yet) is to have my driveshaft rebalanced and to add in a stock transmission mount filled with window weld.

The reason I post this in the PCM thread as opposed to drivetrain is I know everyone here has chased down false knock and I want to know if I can just tell my tune to ignore knock at a certain speed/RPM when I get HPTuners. If it needs to be moved though, then that's fine. I appreciate the help.

Kyle

 

So you have a knock code? Check for loose flywheel/flexplate

 

All 3 locations with poly mounts doesn't help the vibrator effect...Your g/f may like it, but the knock sensors may not...

 

Detecting knock, real or false doesn't set knock sensor codes or cause the SES to flash or cause your converter to unlock. Flashing SES light is telling you it is detecting real time mis fires. Misfires will keep the converter from locking. Sounds like you are confusing knock with misfires. You need to have a scanner on it when the problem occurs to diagnose the flashing SES/misfires.

 

mannyman84: The condition existed before and after doing the flexplate. I did three passes with a torque wrench and loctite.

Old Geezer: Yeah that's what I figured. The motor mounts HAVE to stay in because I was flexing the header into the floor on stock ones. I will have to see what the transmission mount does when I switch it back to stock.

2xLS1: Yeah, that's my fault. When I looked up the code it just said 'RANDOM MISFIRE' so I assumed that's what it was. It absolutely is detecting knock. I can reproduce the condition every single time like clockwork. I accelerate past the 2000RPM point in 4th gear and let it decelerate, the resonating starts, TC unlocks, SES starts flashing. Even when it's flashing it runs like a dream. I can smash the throttle and it is responsive and healthy. Now the first time it happened, I killed the car and pulled over to make sure it wasn't anything bad. I went home and pulled the plugs and they all still looked decently new. I am 100% sure it is false knock detection I just don't know what angle I need to attack the problem at...

Thanks everyone for the replies.