Ive had a random misfire in this 97 z since I was 17. I have recently replaced the plugs, wires, ICM, coil and complete opti, fuel filter, and the EGR valve trying to diagnose the problem. The car seemed like it ran good but sure enough would show a random misfire after about 30 min of running. I noticed the #7 plug kept fouling. However the entire ignition system was brand new. After about $500 in parts I decided to check my injector wiring, and sure enough the #2 and #4 and the #6 and #8 injector harnesses were flip flopped (2 was plugged in 4, 4 into 2, 6 into 8, and 8 into 6). What I dont understand about this is: werent the 93-95 LT1's batch fire? I dont know of anything else that would be different other than maybe pulse width? Anyways I corrected the wiring and no more P0300.

 

The 93's (only, not the 94/95) were batch fire.... but they didn't have the crank sensor to diagnose misfires, so you didn't notice the minor irregularities compared to full sequential. The irregularities caused by batch fire injection are enough to trigger the random misfire detection, as will getting the injectors out of sequence by hooking up the wires wrong.

Many years ago, I ran my LT1 with the Electromotive "Opti-Eliminator". It had a major weakness - no cam position sensor, so it would index incorrectly (out of synch with the ignition order) due to the crank position signal 50% of the time, and it was possible to notice the incorrect injector order when the engine was cold, and the injectors were firing against the back of cold/closed valves. Electromotive tried everything to make the Opti-Eliminator work with the crank position sensor in the 96/97 engines, and could never overcome the problem..... as long as the injector firing was not correctly synched to the actual ignition firing order, they got the code for random misfires. After 20 or so production Opti-Eliminators, they killed the product. (Same guy who invented the "Delteq"...... )

 

Thanks for the reply man. I guess that definitely explains why the car ran great but kept getting that code.