Topic: Backfiring/stalling

[TexWalther]

Hey guys, having a little issue out of the old jeep. For some reason it has recently started stalling out and/or backfiring during acceleration. At first it seemed this problem just happened when the vehicle first started. i would floor the gas and it would act right for the rest of the time it ran. This problem has since gotten progressively worse. I have taken apart and cleaned the throttle body, and IAC. The TPS and Crank sensor are relatively new, past 2 years.. Last thing i tried was disconnecting the O2 sensor before the cat to see if it would clear up the problem. As of now I am out of ideas, any help would be appreciated.
Thanks in advance

[TexWalther]

Should also mention that it is throwing no codes...

[sharpxmen]

coil maybe?

[TexWalther]

Replaced it about 2 months ago.. honestly think i may have to give in and take it to a mechanic this time..

[sharpxmen]

what about loose connection to the coil, or maybe ASD relay going in and out. other than that fuel pressure, anything else should throw a code i think.

[VA_YJ]

Mine was having the same symptoms, and it turned out to be a loose connection on the coil.  The female connectors on the wire harness were not tight on the male plugs on the coil.  I found the problem by shaking wires while the Jeep was idling.  As far as the ASD relay, you can swap with your horn relay (assuming your horn works well).  The fuel pressure is best checked with a gauge of course.  Good luck!

[grumpygy]

Does it do this when cold or warm.  As in does it run good for a while then start or does it do this right off.

  Why did you change out the coil the 1st time.

[TexWalther]

It doesn't seem to change with temperature. I changed the coil last time because it was cracked and i was losing spark when it was moist out. since my post this morning i have checked the injectors, and checked my plugs for spark. the oddity of the day was when i would slowly disconnect my MAP sensor from my throttle body the idle would smooth out and the vehicle would be more responsive to steady throttle. However i changed that sensor and it is still acting the same way. It is almost like a timing issue on an older vehicle, am starting to suspect the PCM is going bad

[aw12345]

If all the ignition components are in good shape and as you say disconnecting the vacuum hose to the map sensor makes it a lot happier , I would check fuel pressure. Pretty good change the fuel pump is on the way out.

[JohnnyO]

Timing chain could be worn and loose and jumped a tooth.  That would be about the last thing I'd look at though.

[TexWalther]

replaced the fuel pump about 2 months ago. It's when i disconnect the MAP sensor itself that it acts better, not the hose...

[sharpxmen]

replaced the fuel pump about 2 months ago. It's when i disconnect the MAP sensor itself that it acts better, not the hose...

hmm,

1. did you try to measure the map output voltage at all?

2. did you test the tps voltage?

3. did you measure the fuel pressure?

4. did you check the ignition timing? is the distributor rotor positioned properly (did you take the distributor out and maybe missed the mark and it is off by a tooth? that might make sense if by disconnecting the map your ignition timing advance goes to zero although i never tried it to be sure it would explain why it starts to run better if you have the wrong position on the rotor).
 
check those and report back, a cheap timing light is about $15, you'll have to use it in the shade but it's good enough to get an idea what happens when you disconnect the map sensor - don't want to do it on mine so i don't store a code.

also check the rotor position when cyl 1 is in compression at TDC to make sure it's lined up with the plug wire (i think it's marked on the distributor body anyway). And the least likely make sure you got the right firing order (i'm sure you do but who knows)

[aw12345]

replaced the fuel pump about 2 months ago. It's when i disconnect the MAP sensor itself that it acts better, not the hose...

Either one makes it run rich

[sharpxmen]

Either one makes it run rich

he should at least check the fuel pressure when it does that so it can be ruled out or determine if that's the cause

[TexWalther]

Guess I will pick up a timing light and voltmeter on my way to work today... Have a jeep I bought solely for parts that I am probably going to take the TPS off of see if that is the problem.. I haven't taken the distributor off since I replaced the coil so i hadn't really thought to mess with it. I didn't think I could adjust the timing from there though so it is definitely worth a look too.