Okay so i put it in the shop and had them do diagnostic work,they said the Fuel pressure regulator was bad,so its now been replaced.The regulator helped a little bit,restored a small amount of power.Im still having the problem of it backfiring and completely falling on its face after its been driven for about 30 minutes or so.

At this point im totally lost with what to do with it,i need ideas on possible parts that can act stupid after they warm up.The pain in the *** part is that it throws no codes at all,just runs like crap.

I am testing the Ignition control module today and the injectors to see if they have anything to do with it.

Coil,cap,rotor,plugs,wires,O2 Sensor,and now the fuel pressure regulator,all brand new.Also im going to say the Firing order is right ive checked this several times,it is 100% right.

Please help,im about to the giving up point and im just about out of money,and getting deeper in debt trying to get this on the road.

 

Could the cat be causing a restriction once it gets good and hot?

 

Did you change the plugs after the FPR was repaired? or could they still be fouled?

 

Two things:

1) Have you tried pulling codes by flashing the SES light?

I inherited some problems on an '89 I acquired a couple of years ago, and today's "modern" diagnostic equipment returned NO codes, even though it was obvious that something was wrong. So I went back to the good old fashion way--flashing the SES light, and I got 4 codes, all pertinent to the problems I was having with the car. And your shop probably used "sophisticated" equipment, rather than flash for codes, so that's why I asked...

2) Regarding "falling on its face," does it do this during all throttle conditions everytime you drive it, or only under certain conditions, such as moderate-to-heavy-throttle-only? And when it acts-up, are you getting any engine knock? Because a bad, disconnected(unplugged or broken wire), or incorrect knock sensor(305 and 350 used different ones) can allow such a drastic change to occur under moderate-to-heavy throttle, after sustained "pinging." Then if you shut the engine off and restart it, all will be back-to-normal... until it experiences the appropriate throttle condition again. No specific amount of running time is needed to cause this, but the engine will have gotten hotter under such conditions, which could be equated to the "warmed-up" condition of having been running for a period of time.

This condition should cause the SES light to illuminate, but not always. And even if it did light-up, it wouldn't return after a restart, until the conditions are met again. So diagnosing this electronically isn't as much a "science" as diagnosing other problems.

Another reason this seemingly-obvious condition can be misdiagnosed is because when engine knock occurs, people tend to think of timing and/or ignition, and rightly-so, usually. Afterall, who would think of something as simple as the knock sensor?

Any chance you or a shop replaced the starter before this began occuring? The starter and the knock sensor are very close to each other, and I've seen knock sensor wires get broken during the process.

I realize this is probably a long-shot, but there's no better way to describe the condition than "falling on its face," because that's exactly what it would be like, which is why this came to mind.

 

Thanks to everyone who replied,its back on the road now.Ended up being the ignition control module that i had tested about 2 weeks earlier not knowing that they needed to be tested more than once :/

Only problem remaining is a loss of a lil power that i believe the distributor is the cause of,theres some rust all inside it,getting a MSD this friday so hopefully that will help it.

Once again thanks to everyone for the help.