Has anybody seen knock like this?
RPM\MAP 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
400 0 0 0 0 0 0 0 0 0 0 0 8 0 0 217
600 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
I can't tell if this is spark knock, or a rod knock. It is only on
decel. I rev it to about 3,000 rpm, then lift a little and it does it.
I was able to capture it in a datalog today. Never noticed it before
Plugs show no signs of detonation. Might have spun a rod, but my oil pressure is 30psi hot idle, 55psi hot wot.

 

Well, you didn't give much to go on for an ECM, vehicle, engine and such. However, your sig talks about a TBI setup. So if this is an TBI setup with the 160 baud ALDL rate, it is very possible (likely) that the knock occured at a different RPM & load value. The data stream takes nearly 2 seconds to output 1 frame of data.

A lot can happen in those 2 seconds. Which means that the event at the beginning of the frame occured almost 2 seconds before the event at the end of the frame.

At the same time it may also be false knock. Loose brackets, bad alt, P/S bearing, exhasut too close to frame, can all cause false knock.

A rod knock is rather loud, so unless running open headers, you will hear it.

RBob.

 

Sorry about the lack of info. 91 GMC K2500, 355, 7747, $42.
Today I tried to remove some timing (4 degrees), no change. I have always had a hot restart knock (4-5 counts and very audible) since I started tuning this motor. I could never seem to find out how to cure it. The newer GM stuff already has a start knock from new so I figured it was ok.
Thanks for the reply, I lurk around here every day and have learned alot. I just don't post too much.....
Randy

 

Ah yes, the 'ole hot restart rev-em-up and knock trick. The only way I found to help this on a stock '747 was to lower the IAC park steps. Try setting it to 90 or so for the summer.

Once the cold weather kicks back in (a long while from now I hope!) will need to increase the park steps again.

RBob.

 

Here is a log from today, even with less timing there is sporatic knock all over
There is nothing loose or hitting any where I could see. I also swapped in my stock bin and still have knock. But I also lost tons of torque, so I put it back to the current tune. This current tune never had any knock all summer or winter. I just don't know what has changed.

RPM\MAP 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
400 0 0 0 0 0 0 0 0 0 0 0 0 0 25 569
600 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
800 0 0 0 11 0 0 1 14 0 0 0 0 0 0 0
1000 0 0 0 0 0 17 8 11 0 0 0 0 0 0 0
1200 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1400 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1600 0 0 13 0 0 0 0 0 0 0 0 0 1 0 0
1800 2 0 0 0 0 0 1 1 0 0 0 0 0 0 1
2000 7 4 0 0 0 0 0 0 2 1 1 0 0 0 0
2200 5 7 6 1 1 0 1 0 0 0 0 1 1 0 3
2400 13 1 1 0 3 0 0 0 1 0 0 0 1 0 6
2800 16 0 2 0 0 0 0 2 0 0 1 1 1 1 1
3200 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
3600 20 0 3 11 0 0 0 0 0 0 30 0 0 2 0