2 weeks ago car running fine. Driving home from work engine stalls 2x, cranking several times finally starts. Get home turn off engine, now cranks but no start.

I replaced the opti, opti connector and external ignition module. (The coil is 6 months old) Now car cranks and tries to start, stumbles and sputters terribly.

I have 1 engine code, 420, which has been on for a few months. Fuel pressure is 50 psi when I turn on the key.

Any ideas would be appreciated. Someone told me MAF sensor is bad... wouldn't that trigger another engine code??

 

Well the P0420 code is catalyst system efficiency below threshold which means the downstream o2 is not satisfied with the work the converter is doing. Could be a number of things including converter iself or possible o2 but will not cause a no start. Always when diagnosing a no start condition you must start with the basics to make fire, spark fuel and air. You said you have 50 psi fp which is good but you need to be able to find out if the injectors are firing, the best way to check is a noid light and cranking.(Can find noid light kits at parts store pretty cheap) Obviously you will be wanting to check to find out if you have spark. You can start at the coil wire, if you have spark there but not to plugs then check opti/wires. Even though parts are new doesnt mean that couldnt have failed. Sounds like it could possible be a ignition module tweaking out but that a lot of times happens with heat and when they cool down they will again function. Hopefully something here can help you and good luck.

 

What led you to replace the opti and ICM - did diagnostics lead you to those, or did you just try parts replacement to solve the problem?

When you intalled the opti, are you sure you got the dowel pin in the correct hole?

50psi fuel pressure at the turn of the key seems excessive. System is supposed to run at 43.5psi, with the specs 41-47psi. Not likely to keep it from starting, but worth checking out when you do get it started.

 

What led me to replace the opti was a no spark/no injector pulse condition. I borrowed a noid light kit and discovered no injector pulse. I checked for spark and had no spark as well. I was told if ignition failed that would shut off the injectors.

Before I replaced the opti and ICM the engine would crank and not attempt to run. Now after the repair, it cranks and attempts to start and stumbles terribly.

As far as the correct hole for the dowel pin, I carefully checked the location of the dowel when removing the old opti. There are 3 possible holes for the dowel on the back of the opti, 2 holes look "hourglass" shaped, 1 hole is not, this is the hole I used.

Thanks for your help so far...

 

Ok, here was the problem... Seems that the brand new opti that I installed was NO GOOD. We suspected the opti again when the timing on the car didn't retard when cranking. It just stayed at 12 degrees.
Another brand new opti installed and the engine fired right up!

 

What does the Opti have to do with retarding the timing for start? That is set by the PCM.

 

So the opti was making your car misfire and run rought? My camaro is running rought and it has stalled a few times, then when I go to turn it on sometimes it just truns over but it doesnt want to start.????

 

@ Injuneer, I am not an expert on these engines. I'm just an enthusists that enjoys working on my own car. My post was based on the problem I saw and I wanted to try to help others understand their problems. I guess I stand corrected. Either way, my problem is solved and the engine runs fine.

@ dirtgar, My experience with the Opti is this... It either works or it dosen't. I've had my 96 Z28 for 1 1/2 years and replaced the opti 2x. Both times the engine cranked but would not start. During the 2nd replacement, I bought an Opti that was defective. The engine barely started and stumbled badly. We suspected the opti again, replaced the brand new but defective unit and the engine fired up.
Good luck with your issue. This site is a great tool.

 

Did you check fuel pressure??

 

Did you buy a GM opti or one of those $130 units?

 

Glad you got the problem fixed but why not also check the coil in a no spark condition? Just a thought to others who read this thread, include that in the diagnostics.

 

@ moparman, 1st opti I bought was from Summit Racing. It lasted 8 months or so. 2nd opti was from my local parts dealer (not a chain store) it was manufactured by Cardone. That one was defective and they gave me another and that one worked. If this one fails, I will go to see the General, but that's prob some big $$$.

@TDavanzo, This thread obviously does not contain all my troubleshooting efforts. I checked fuel pressure, spark, replaced the ignition module, the coil was new 8 months ago when I changed the opti the 1st time. Also had the car hooked up to Tech2 computer that is commonly found at GM dealerships looking for potential problems. My parts supplier was kind enough to lend me a new MAF to see if that was a problem, just cause I knew 96 was 1st year for OBD2 and I wasn't sure if it was advanced enough to see all sensor failures. Luckly I have another vehicle to drive, so I spent several days diagonsing the "no start" problem. Knowing the old opti was only 8 months old, I didn't think it would have failed in such a short amount of time.