YJ 2.5L hesitation/ backfire

[centralmax]

I recently had a 1994 mpi 2.5L YJ.. yes YJ fall in my lap. NO wrangler forum has members as badass as naxja so heres my problem.
When i first got it she had 60 psi at the fuel rail causing it to backfire and hesitate under accel. I blew out the fuel lines and it was a clogged fuel return line that fixed it.
Now the psi is right at 31 but it has slowly returned to the old problems. If i push the gas pedal down 1/2 or so it will accel. smooth and slow. but when i give 2in. or more pedal to accel. faster, it boggs and backfires until above 2500rpm or so then smooths out and goes like hell. It is running rich at the exhaust tip and i had black creasote on the tip of the exhaust.
My fixes: not plugs or wires, fuel pressure at the rail, o2 sensor, idle air control valve, throttle position sensor.


IM LOST HERE!!!!!!!!!!!

thanks,
damn YJ

 

[87manche]

timing or low speed ignition miss/weak spark would be my guess.
See what the spark looks like, if it's yellow it's weak, and may not be enough to ignite a rich WOT mixture, it should be thiick and blue.

 

[centralmax]

ok, will check that.. any other ideas....?

 

[DesertYJ]

I know you said it was not the O2 sensor, but I would suggest you double check that.

 

[Luggz]

MAP sensor on my YJ was doin that...

 

[centralmax]

I replaced the O2 sensor about 400 miles ago.. it helped then, but not the symptoms r different thats why i assumed it wasnt that. Is there any way to test the MAP sensor?

 

[DesertYJ]

I replaced the O2 sensor about 400 miles ago.. it helped then, but not the symptoms r different thats why i assumed it wasnt that. Is there any way to test the MAP sensor?

Yes.
The repair manuals (Hanes, Chiltons) you can buy at parts houses will walk you through testing the O2, MAP, Crank, and other sensors.
Sorry but I don't have mine with me here in Iraq.
You will have to go and pick one up and read the book.
The intenet is cool :compwork: but so are books.:read:

 

[centralmax]

FIXED IT!!!!!!!!!!!! IT was a pin hole leak in the intake manifold to MAP sensor vacuum line. RUns like a wimpy 2.5L should now. thanks for the help