I need some help with this one. 93 T/A A4 65000 miles, slp cai, magna flow cat back, hypertech thermo master, 160 degree thermastat. The car is having heavy detanation under heavy load such as line lock. Also driving along easy, if stepped on hard it detinates and misses really bad. It also detinates lightly while in park if you goose it. I removed the chip and the thermastat and there was no change. Replaced the plugs and wires with oem, also checked knock sensor and circuit and still no luck. Egr system and most everyother sensor and circuit. Used jumper wire with no code showing. Replaced O2 sensors, car ran better but didn't solve the problem. Three different brands of premium gas. Plug #6 had hard black crust **** on it. Drivers side oxygen sensor had light white powdery stuff on it and passenger side had carbon build up on it. Used a top end engine cleaner. The car runs great other wise no misses or knock if i go easy or when the rpms are up. Cap and rotor 2 yrs. 2500 miles ago.

 

I suggest replacing your fuel filter, checking your fuel pressure with a gauge, and checking your air filter. If you have a friend with a similar year Z28, you might swap coils also to see if that makes a difference. Usually coils fail that the car doesn't run though. Also double check that all your wires are fully seated on the spark plugs and opti...you should hear a click when they are seated.

 

New fuel filter, fuel pressure is fine, air filters are clean. I have checked wires a couple times. the car was running like this before i replaced the plugs, wires and 02's. Will the icm or opti. cause these problems.

 

The opti is always a possibility; ICM 's aren't a common failure. Have you checked your fuel pressure under load or only at idle? I'd attach a gauge to the schrader valve, tape it to your windshield and drive around while monitoring your pressure. It could be that your fuel pump is "weak" and can't maintain pressure under load. What spark plugs did you use? When my engine was basically stock, I tried a set of Bosch platinum plugs and the car ran like sh*t! Replaced them the next day with AC Delco platinum and the car ran great!

 

Have you checked to see if your plug wires are in the firing order. #7&8 crossed will do that.

 

Thanks Guys, The fuel pressure is ok with key on, and engine running. can't check while driving because the fuel valve is near the pvc and the hose on my gauge does't reach. the fuel pressure stays ok when i load the engine with the brake while standing still. The plugs are ac delco platinum 50 gap. Wires are also ac delco. I checked the wire a couple times thay seam fine. This may help, When the car is cold and on high idle i can melt the rear tires no knock. But once it reaches operating temp. and the idle comes down it just knocks and misses. The temps. seem to stay ok and the fans work fine. Why would plug #6 have this hard black build up on it. while The others where fine. The o2 on #6 side had a fairly heavy build up of carbon while the other 02 had a white build up very little though.

 

Ok i checked the fuel pressure this morning with a gauge with a longer hose. 39 lbs at idle then goes up 3 or 4 lbs when i step on it. Knocks and breaks up realy bad even at 1/4 throttle. Shoud i pull the opti. out and look at it? Or should i buy a scan tool such as autoxray 3000 or is their a better tool. I have a laptop. This car runs great before it gets up to temp.

 

I would definitely invest in a 90 ALDL to laptop cable and a trial (free) version of TTS Datamaster to see what's going on. Sounds like your fuel pressure is doing ok, and if the plug wires are all routed correctly, I dunno.

If you're noticing the fouling/crusting on just one or two cylinders, I'd say do a compression/leakdown test just to be sure.

 

Well i pulled the opti. out and WOW. It's burnt, and the rotor was rubbing the cap so bad their are deep grooves in the cap at the #6 terminal. The rotor is so worn the metal striker is ready to fall off. Where is the best place for a complete oem one. Thanks for all your help.

 

Jason Cromer @ Sam Taylor Buick Cadillac. Non-Vented Opti will run you about $320.

 

for future reference, I've had alot of cars knocking (audibly) due to over active PCV's. They draw oil in the intake and lower the octane rating of the fuel.

It was so bad on our 01 LS1 that it would spark knock with the factory 22 degrees of timing.

 

Hows the car running now? Check out speeddensity.org if you need any more help with it.