I tried to post this early this morning but must have done something wrong. Just a little background as I know it helps. I am 63 years old and have owned my 1989 Firebird GTA for over 20 years. It is not a daily driver and just a big boy toy. I drive it maybe 1000 miles a year now.
Over the past 20 years I have done a lot with the car. Sub frame connectors, new lake wood traction bars, brakes, sway bars, monster 700r4 transmission ect. The engine is now a 383 which was built by a very good shop in my area. He builds stock cars, drag cars and even drag boat engines. I have no smog stuff left on the engine at all. Air pump , EGR and Cats are all gone. I am running a new BBK throttle body, adjustable MAF(never been adjusted) , SLP runners, SLP headers, Hook cat back system, 26lb injectors (tried 30lb and took them out) ZZ4 cam with roller rockers and harden push rod with guides, 7 quart oil pan with a high volume pump, I have also had several chips burned for the car as I made changes. I can't remember right off the top of my head the company name but the guys name is Ryan. The chips have always been fine. Now here where I am, last fall we went for a ride and was just crusing along at 50 mph and the car cut out once and then just died. I ended up getting flat bedded home. I have a nice garage and most everything I need to work on stuff. My first thought was it was the control module in the distributor and I have had them go bad before. So I put an accel one in and no difference at all. Then I thought maybe the pick up coil or regular coil. So I decided to just replace the distributor and coil as they both had come from e-bay and I herd that stuff is junk. So I contacted Jeg's and bought top of the line stuff. So I pulled out the distributor and changed it and the coil and the car started but run badly. It was near winter so I just let it set until this spring. In the mean while I pulled the tune port off and sent it out to be powder coated which is something I always wanted to do. When I put every thing back together I decided to change the throttle position sensor and air control motor being they were right there and years old. I set everything up by the book. I also decided to pull the distributor again as I thought it may be a tooth of which it was. So they everything started and ran fine but the service engine light came on. Went for a ride and the engine ran good for a while and then all of a sudden it acted like the ignition just died for a second the tech dropped but then everything was fine for a while. When I stand on it ,it does not miss a beat. Revs right up to 5700 rpm which is where the shift points are set. On the low end it has everything you want. I can break the tires free at 10mph. But every now and then the ignition just plain fails when you are just riding along. I checked the codes and the only code is 12. I am open for suggestions. Is it a wire somewhere grounding out or something? What about a loose plug? I am stumped and don't have a clue where to look. I can start it up and it can sit there 20 minutes and run fine. Somethings I can go out and nothing happens and sometimes it drops the ignition and I fear the tow truck again. These on and off issues are hard to find and you guys know these cars better than anyone. Thanks

 

wow, you wrote a lot!

 

Does "a wire ground out" at some particular engine RPM? Reliably, every time, take it to the bank?

No.

Your problem is probably not that.

Code 12 = "No Reference Pulses". Which means, the ECM can't see that the distributor is turning. It's not sending out the signal that says that. COMPLETELY OK for a motor that's not running. Obviously, if the engine is spinning, not so OK.

Can't say what might have happened all about "powder coating" and all that. LOTS of opportunities for solutions involved there.

Personally, I'll take troubleshooting a "no start" ANY DAY over a "runs like crap". No-start ALWAYS means one of The Big Three - air/fuel, spark, compression - is missing. Doesn't get much eeeeeeeeeeeeeeeezzzzzzzzzzier than that.

Compression doesn't just "go away" in an otherwise perfectly running motor, unless the timing set fails. EEEEZZZy enough to see that by watching the distributor. Does it turn? Does it point at the #1 cyl at #1 firing over and over again? OK, not the timing set. Not a "compression" problem.

That leaves air/fuel, and spark.

Does the TB open fully? OK, not air. Either fuel or spark now.

Spary some starting fluid, or gasollne, or MEK, or whatever VERY FLAAMMABLE substance, into the TB. Does it start? Run for a second or 2 and then quit, or, just not ever hit a lick AT ALL?

Runs for a second or 2 = YOU HAVE A FUEL DELIVERY PROBLEM.

NEVER EVEN TRIES TO RUN = you have a spark problem.

Go do this EXTREMELY SIMPLE thing and tell us what happens, and we'll tell you whether you need to be working on the mechanicals of the motor, the fuel system, the ignition system, etc. It's just TOOOOOOOOOOOO EEEEEEEEEEZZZZZZZZZZZZZZZYYYYYY. It's just a no-start. The eeeeeeeeeezzzzzzzzzzzzyyyyyyyyyest thing in the whole hot-rodding universe to troubleshoot.

NOW... if it graduates from a "no-start" to a "runs like crap", that's a horse of a different color. BUTTTT: one issue at a time. Let's get it to run, then if it doesn't run RIGHT, figure out WHY.

 

Car runs fine 90% of the time and just dies all of a sudden. I am sure it is some kind of ignition issue. Why code 12 even when it is running fine? This car runs like a raped ape and then just cuts .