Weird backfiring issue. Any suggestions??
 

Hey guys,

I have a 93 with PFC, and reliablity mods. 25K on rebuilt engine, etc.

Lately I have had an issue where once the car warms up, sometimes it will turn off/backfire, then I wait about 30 seconds to 3 minutes and it will run fine then do it all over again, the longer it runs the worse it gets. Also the radio turns on and off (I think this is a seperate issue from the backfiring though)

Everything is good at the battery, starter, and alternator.

Would a clogged fuel filter/ or bad fuel pump do this? Grouding issue?

Any help would be greatly appreciated. Carll

maybe ground wire loose.
whats the a/f say?

What you mean by "sometimes it will turn off/backfire..." u meant the car itself? or accessories? What have you done to it recently? Have you tried pulling codes? Because it seem liked you've set ur cat to a limp mode like i did to my car when I changed my fuel filter by unplugging the fuel pump relay to release fuel pressure. So there might be a possibility that if you've done something to your car, and accidentally set a code that you're unaware of, which will cause the car to run crappy and backfires. If theres a code, try detaching the ground cable of the battery and step on the brake pedal for about 10-20 seconds. Attach the ground back and drive the car above 40mph and see how it goes. Let me know how this works out. Pm me if needed.
-Eric

Clogged fuel filter = restricted fuel pressure, can cause blogging, lack of power, and even stalling. A possible issue for your problem.

Bad fuel pump - excessive fuel pump pressure - causing the car to run richer than normal, but will not cause the car to stall or lack of power like you've described. But it is so excessive that fouled a spark plug, which might foul a spark plug, can also caused the car to have lack of power.

Bad fuel pump - not providing enough pump pressure - resulting a leaner mixture, lack of power, but will not stall. But if too lean, it can create a tremendous of NOx which will result in a melt catalytic converter results in blogging and lack of power.

Grounding - Please verify you ground cable on the battery is good. Make sure it is not corroded somewhere hidden which you did not see. And since you've verified that the battery, starter, alternator is good. It is possible that you've got a ground somewhere which can sent false signal to the PCM creating this issue.

Hope this helps a bit.
-Eric

P.S. Sorry for the double post, should've replied everything in 1 single post =D

Thanks Eric. I know fuel must be getting cut off somewhere, ie the backfire. I have nippenso? fuel pump off a parts car I bought, this may be a good time to install that. I'm pretty sure it still has the stock fuel pump/filter on it with 118k on it.

I put a stock ECU back in and it threw codes but I was told by the tuner that with the mods my car has, it would throw these codes anyway and the pfc would eliminate them.

Grouding at the battery is perfect, it has a new terminal,etc.

I doubt it could be a spark plug/wire because it will run bad then perfect all the sudden.

25K on a engine rebuild, wtf is it made of....gold!

No problem.

But from the number I saw here, 118k is pretty high not to have a fuel filter replaced. I've actually did mine 3 weeks ago, and I've noticed a quite a performance differences after I've replaced mine. I.e. faster response on throttle reactions, and the car just seems faster and quicker. And when I pulled that thing off, man, it was dirty. All the stuff that came out of it is dark brown... like nasty!

I'd think it was fuel if it was down on power or sluggish but thats not the issue, it will go like stink until it turns on and off/ and backfire. That makes me think its an electrical issue.

If it's built right!!! And you don't abuse it and don't run a ton of boost they will last a while!!!

I think he was referring to 25k as being how much you spent on the rebuild...miscommunication.

are your coils in the stock location maybe 1 of them is cracked and only arks when warm sense it sets on top of the motor??

if that makes any sense

Good point! Do I have to take off the UIM to take out the coils?

yes

Rotaries do back fire evey once and a while, it happens with a fuel thirsty engine. However, they shouldent backfire excessively. Over the years, I have had some backfireing prolbems, each with a different cause. The causes I have been able to find are:

-faulty knock sensor
-spark plugs covered in carbon
-old coils

It was the damn alternator!!! The monkeys at advance auto parts said it was good too, now I know to double check stuff!

I was going to recomend the wireing and it would cause radio to quit as well.

how did you find out it was the alternator. for future searchers =]