I have a 94 Z28 with a 383 LT1, Msd ignition, BBK headers, throttle body, intake, injectors, mailorder tune, etc. I purchased it like this. One day, out of the blue, the motor started missing and backfiring. For example, When your cruising at highway speed on level ground with neutral throttle, you can feel the engine hesitating and the instant you give it throttle, it clears up and accelerates til you return to neutral throttle and it does it again. Also, when under moderate to hard acceleration, the engine is popping and backfiring and hesitating slightly, yet still accelerates quite rapidly. Just not quite as fast as it does when running properly. The backfiring and popping seems to be coming from under the hood area. Cant tell if its from the intake or the headers/Y pipe. The check engine light also comes on and goes off intermittently while driving. Any ideas on what this might be? I can tell you that the car does need a chassis dyno to give a proper tune. It does run slightly rich. Any and all suggestions will be greatly appreciated.

 

First thing is to get the codes pulled.

 

Can the scanner read the codes even though the light isnt on? Does the computer store the codes?

 

Not for sure about the OBDI, but the code(s) should be stored.

 

Yes, ODB1 stores codes and can even store codes that don't iluminate the SES light. Step one is to check for codes.

Do a quick glance of the spark plug wires to make sure one isn't burned or worn through. Pull a plug and look at the gap...since you're running a modded engine I suspect you're running one heat range cooler plug at a gap of about .035".

Good luck!

 

It could be either you opti on its why out and will throw a Hi-RES code.

Or it could be you opti harness thats old.

Listen for vaccum leaks... My Buddy has a WS6 and was having the same kinda problem your having I told him to check for vaccum leaks and it ended up being his rubber intake not be properly on... It gave him the same symptons of an opti going out he said.

 

I assume your talking about the opti-spark distributor. Everything was replaced with MSD components when the engine was done, approx. 5000 miles ago. I had a burned wire, awhile back, and a non firing cylinder. Didn't run anything like it is now. Fixed it and replaced all the plugs. I know that one of the O2 sensors has a wire thats barely attached. Could this be a problem?

 

Instead of guessing, you really need to get the codes pulled. It might be the O2, or it might be something else. If you can get your hands on a scan tool, it would be obvious if the O2 is screwed.