Engine Knock Problem

Spark knocks (detonation) under high loads at WOT

Please Help!
My SC has a knock I cant fix! It spark knocks (detonation) under high loads at WOT and near WOT. Particularly after shifting into 3rd gear(AOD). This car ran great: 14.08 at 97MPH. Then suddenly it started knocking, that is something changed or broke.
These are the Mods. 1995 supercharger 10% pulley, 42lb injectors Pro-M 80mm meter, 255L fuel pump, IC fan, Custom 3" exhaust, adj. fuel press. reg.,EEC tuner, etc. I checked the fuel pressure while driving, I have 55-60PSI at WOT, 37psi at idle vacuum connected, and 42psi vacuum disconnected. I checked the plugs, they look great, lite tan-off white, no burned tips, all looked the same. I put in new Autolite APP 764 short reach .045 gap plugs, it ran a little better, but no improvement in the knock problem. I tried a different Mass Air Meter, no change, I tried several barometric presure modules, no change, I checked for vaccuum leaks, found a minor one, but I did not help the knocking. The Heads were rebuilt about 10,000 miles ago when I blew the head gaskets running a 10% pulley with stock exhaust. Sometimes I get smoke out the tailpipes when its cold,which indicates running rich which seems contrary to knocking. I ran scan tests, KOEO, KOER, checked the timing at idle with spout disconnected, 10 degrees as specified, and 30 degrees with KOER test. I have a brand new Magnum powers blower, intake, and Throtle body that I dont want to put on until I fix the knock.
As I understand it knocking is caused by too much spark, not enough fuel, or glowing deposits in the combustion chamber. As the plugs all look the same I think it must be fuel or spark. Could a vacuum leak before the supercharger cause it to run lean enough to knock at WOT and still run good under normal driving? How would I diagnose this?
Thanks
David

David,

I see that you list an EEC tuner in your mods...how much timing are you running at WOT ? I would suggest dynoing with a wide band o2 to see what your A/F ratio looks like at WOT. I'm betting your lean.

To prevent serious damage to your engine, pull the octane plug to retard the timing. I think it pulls about 4 degrees when the plug is removed. The plug is located near the EEC test port on my 91 SC. Here's a picture.



David

Detonation at WOT

Thanks for the reply.
I have the octane plug pulled, and it knocks less. The ECC tuner is set up with stock timing and fuel parameters, except for the Mass air, which is set to the pro-m test results. I had this file made up to test my problem. When I ran aggressive timing with the EEC tuner it knocked a whole lot more. TO avoid writing a book, I only listed the most basic things I have done. I would appreciate more advice. I want to get back to the Drag Strip! I am going to try the dielectric grease on the plug boots that was recomended in an older thread concerning detonation. I am also going to try checking for more vacuum leaks and check the air temp sensor.
Thanks
David

Detonation at WOT

I did run on a dyno with wideband. And I ran 12% across the whole pull. That seems about right to me. Should an SC run richer than that?

Just curious to see if your temp sending unit is accurate. Would hate to think you are running hotter than normal without you knowing about. Just guessing here. GL

Double check your Evap line making sure it is intact and isn't kinked or cut or something.