89 Firebird, 355 TPI - I've been trying to diagnose an afterfire situation for a couple weeks now. Initially it was so bad I couldn't hit the gas without dumping a half gallon down my headers and having it all explode at speed. I replaced the knock sensor and have calmed this down somewhat, but the car is still basically useless on the road as I am still losing power and having my fuel explode in my pipes. Below is what I have checked and the result:

-fuel pressure ok
-injectors all ohmed 16 cold, 17 hot
-battery/MSD connections solid
-plug wires not burned through/ohmed ok (MSD 8.5's)
-plugs look almost perfect
-valve springs ok/not broken
-no exhaust leaks (that weren't there before this started)
-O2 sensor connections ok, sensor working correctly
-knock sensor ohmed infinite resistance, replaced with new (scanner shows normal knock counts, with little to no timing retard when "it happens")
-coolant temp sensor ohmed cold (4.72) and hot .25 - ok
-TPS was a tad low, adjusted to .49
-ignition coil ohmed ok both cold (.5/5.4) & hot (.5/7.0) (Blaster 2 GM) on both primary/secondary
-distributor cap & rotor looked ok
-ignition module tested ok (Advance Auto)
-pickup coil ohmed 830 (could not see to check for breakage)
-base timing was 8*

So all this checked out ok, what more can I look for? Can I test my MSD box? Also, I'm not sure what compound I used under the Ig Module last time, should I use Dielectric grease, RTV blue, or the silicone grease that was unused from the module when it was new?

Something I thought peculiar, when i had the gun on the timing mark, I noticed it would "spike" or jump (to about 15* or so) every couple of seconds. For those who will ask, the EST was disconnected. Also, Vader had suggested I disconnect the EST when my problem crops up and see what happens. I did and it was still happening..somewhat. It did calm down a bit but I could still feel a bit of fire in the pipes, but it wasn't dropping the RPM and actually popping.

I don't wanna fight this for another 9 months like I did on that stupid pulsator issue I had last time. Please point me in the right direction!!!

Thank you...
Eric

 

Can anyone please help me with this?