junkmaro

Alright this is a little confusing but I have a 1997 camaro z28 with a 1994 lt1 new Opti new coil it does still have the 97 computer which I’m thinking is the problem just because of the differences in between the 93-95 and the 96-97 all it does is backfire through the intake and out the headers I also haven’t ran all the vacuum lines but I did plug them trying to get It to at least try an start but still just back fires an all the modifications I have is speed engineering headers, msd wires, and egr delete thanks in advance for all the help.

Injuneer

Are you sure you have the splined shaft for the new Opti indexed correctly to the cam sprocket?

http://shbox.com/1/93-94_opti.jpg


All the plug wires routed to the correct plugs?

junkmaro

Not positive of the Opti being indexed correctly but I know the wires are run correctly.

Injuneer

Approximately 10% of the Opti installs manage to incorrectly index the “odd” tooth on the splined shaft to the notch in the cam sprocket. In theory, that isn’t possible, but based on the number of times I've seen it happen over 20+ years helping people on this site, and others like it, it does happen. If it isn’t indexed correctly, the spark timing is off, and you get backfiring and popping.

What brand is the Opti? Did you loc-tite the rotor screws? Cheap Opti's (or even a $500+ MSD) can be bad right out of the box, and the screws falling out of the rotor can happen to any brand. Those issues can also cause your problems.

junkmaro

It’s a jegs Opti. It is good really good spark an sometimes acts like it’s gonna start but only backfired after you stop cranking.

junkmaro

What sensors are different in between the 94 an 97 I’m running mostly the 94 sensors could that be the issue?

Injuneer

The 94 does not have several sensors, none of which affect the way the engine starts or runs:

- after-cat O2 sensors (only there to sense if the cats are present and working)

- EVAP purge line vacuum switch

- crankshaft position sensor (used only to detect misfires in OBD-2)


You can get codes for those sensors, so it’s a good idea to have them “tuned out”.


- resistance of the knock sensor is different (93-95 = 4 Kohms; 96-97 = 100 Kohms)

If you are running a 97 PCM, your engine needs to have a 96/97 knock sensor.

Shoebox has the 94/95 PCM pinout diagrams, marked in red to show the 96/97 differences.

4th Gen LT1 F-body Tech Articles

junkmaro

I’m using the 94 knock sensors could that be the issue?

Injuneer

If you use the 94 knock sensor with the 97 PCM, you will likely get code P0332. That code doesn't turn on the SES light. When it sets, the PCM is going to retard the ignition timing based on engine load, RPM, coolant temp, etc.. I don't know if it does that during cranking. To eliminate this as a cause of what appears to be incorrect ignition timing at cranking, replace the KS with the correct 1996/97 piece.

junkmaro

Replaced the knock sensors with the 97 ones I had now it back fires immediately when cranking.

Rhansen

Sounds like a timing issue to me, if you are certain that plug wire routing is correct then you should verify correct indexing of the opti.
If the opti is indexed correctly the next thing I would check is that the valves aren't adjuted to tight. Hard to get compression if one or more valves are hanging open.

junkmaro

I’ll check to make sure the opti is indexed correctly next thanks for the help.

junkmaro

Could it possibly be bad gas? this car has been sitting for awhile don’t know how long exactly but probably 4-5 years with a half a tank

Rhansen

if the car fires/runs with a little starting fluid through the tb then I might suspect bad gas

junkmaro

The opti slid right into place that’s why I’m kinda confused on how it couldn’t be indexed correctly. But it has started before on starting fluid then I lost spark because of the opti spark wiring fixed that and I got spark back an now it’s back firing.