Random stuttering and stalling

[immacomputer]

Hi, going to try this again. My '95, stock KA24DE, 240 has been pissing me off for over 6 months now with this lagging hesitation stuttering bullshit. Sometimes the car runs perfectly normal with no back firing or issues and then randomly while driving, it will start to stutter with constant throttle. When its in this mode, it will stall if I put in the clutch. If I keep it in gear and slow down, it will backfire extremely loudly at 2k and 1k rpm. It never backfires when running normally.

It's not throwing any codes anymore and I've replaced the distributor, O2 sensor, IATS, MAFS wiring, coolant temp sensor, spark plugs, cam position sensor, knock sensor, and timing chain. What could be causing this??? It's driving me crazy... I want to sell the damn thing but it probably needs to be running consistently to get any money out of it.

Any help would be greatly appreciated. I'm hoping it's not wiring issues but I'm out of ideas and my mechanic friends are also stumped and pissed off as it's making them feel stupid.

[Ka-t in progress]

Have you checked the maf itself? But it sounds to me to be fuel related. I would check the fuel pressure at the rail, and check the injectors for a leaky o-ring,and fuel pump/filter. It could be dropping pressure at the pump or a clogged fuel filter could be the culprit. Hope this helps!

[Ilya]

Is your exhaust black? as in: the muffler tips and as far as you can see inside the muffler? I agree, back fire = a lot of un-burnt fuel in the Exhaust.
Possible Causes:
-FPR
-Leaky injector
-Leaky injector Oring
-Bad Vacuum leak causing your car to run extremely rich(egr, bpt valve, vacuum hoses)

Get an FSM for the S14, all instructions are in there. I just replaced all my injectors because my car would run extremely rich, bad mpg, black/smelly exhaust, but drove fine; turned out one of my injector pintle caps was broken so the injector was leaking but i had no way of telling without replacing them all.

-This weekend I built a smoker out of a Air Mattress Pump, 1 quart paint can, and some barbed hose nipples from lowes all for 10 dollars. Hooked it all up to my Brake Booster hose and saw where the leaks were, BPT Valve, some other small vacuum hoses.
http://www.fiero.nl/forum/Archives/Archive-000002/HTML/20130314-1-081547.html

Good luck, dont give up, and remember, if you dont have money, you should not own a car...the only way to make money is to invest some money

[stigo]

I agree that is probably fuel related. Also you can try to have a friend let you use his ECU and see if a may be that? Doubt it but you can rule it all out.

Also Ilya that smoker machine for vacuum leak detection looks good. I'm going to try this weekend.

[immacomputer]

Thanks for the replies! Having a car is required for me to get to work. There is no public transportation where I live and the commute is far too long for my mountain bike lol.

Fuel rails were 41 psi I believe and factory spec was 42 so I think I'm OK there.I don't think there are any vacuum leaks as the car idles and runs great when not in crazy mode. Most of the time its perfectly fine.

My mechanic friend said he had a scope and scanner and said he saw spark cutting out so we swapped out the distributer. The old one was corroted and nadty so it needed replacing but it didn't fix the problem just made it not as severe.

The only time I get black smoke is when its in crazy mode. If it is loss of spark, could that mimic rich f/a ratios?

Oh and injectors seem to be spraying fine and the fuel filter is also new. Thanks a lot for the input guys, hope this post can spark some new thoughts lol. I might try replacing the egr as everything replaceable on this car seems to be shit anyways lol.

Oh I'm also getting 25mpg and that's with it averaging running normal and poorly. When it runs normal, its really great and has way more power than it did a year ago. Everything we have replaced has improved performance but not fixed this annoying issue.

[Ka-t in progress]

Nothing much really comes to mind unfortunately. Did you turn the key over and inspect the injectors to see if any were leaking? Only other options that come to mind is still the fuel pump, never hurt to check the timing,are you running any kinda of afc or a tuned ecu? I wouldn't hesitate to send Martin at enthalpy an email regardless, he is very smart and helpful,he has straightened out my issues several times with little information about the car. Hope you get it going soon!