Knock after shift... Any one ever seen it?
Thread Starter
Teching In
Joined: Feb 2002
Posts: 49
Likes: 0
From: Music City
Knock after shift... Any one ever seen it? Changes to the car are, shift kit and 75 shot. Before these changes I had 0 knock. Now I am picking up 3-4* at WOT. I have not changed any WOT settings as far as the tune goes. I am thinking it might have something to do with the shift kit. I did two runs. First was from about 45 and rolled through the gear and let off before the shift (did not spray). I got 3* knock. Second was about 55 - 100 MPH. Car kicked down to 2nd gear and I got 0 knock. Shifted to 3rd and got 3-4* of knock that slowly went down to about 2* before I lifted. This run I sprayed.
I know spraying can cause the knock, but if it were the spray, I would have thought I would have picked it up when I sprayed in 2nd gear. All of 2nd was no knock and 26.5* timing. 3rd had knock and the car began pulling timing.
I am going to pick up some octane booster to see if that helps, but just wanted to check if anyone has had this happen due to a hard shift / shift kit?
I know spraying can cause the knock, but if it were the spray, I would have thought I would have picked it up when I sprayed in 2nd gear. All of 2nd was no knock and 26.5* timing. 3rd had knock and the car began pulling timing.
I am going to pick up some octane booster to see if that helps, but just wanted to check if anyone has had this happen due to a hard shift / shift kit?
good catch jimmyblue 
Tip-in knock is not false knock, it's caused by lean
mixture error. Often from the speed density tune
being off. When you shift hard, you might see a
MAP spike (from the air column against a rapidly
slowing motor, perhaps this is your shift kit doing
its job) which would put you into speed-density
mode by the "unsteady MAP" criterion. If this is
your issue then the logs would show a lean dip in
O2 sensor voltage. Slowing the motor from a place
where MAP was depressed (like by intake tract
restriction at the top end) to where it's maxed
(low RPM WOT) might also trip that trigger.
mixture error. Often from the speed density tune
being off. When you shift hard, you might see a
MAP spike (from the air column against a rapidly
slowing motor, perhaps this is your shift kit doing
its job) which would put you into speed-density
mode by the "unsteady MAP" criterion. If this is
your issue then the logs would show a lean dip in
O2 sensor voltage. Slowing the motor from a place
where MAP was depressed (like by intake tract
restriction at the top end) to where it's maxed
(low RPM WOT) might also trip that trigger.
Thread Starter
Teching In
Joined: Feb 2002
Posts: 49
Likes: 0
From: Music City
My O2s are rock solid at 90-93 so from looking at them, I am getting plenty of fuel. I am going back to my last falsh to see if it goes away. Final question. I am still using edit and autotap to tune. Can you do a SD tune with edit and autotap? From doing some reading, it looks like you need to log dynamic airflow which is not on my autotap as far as I can tell. Many thanks.
