88 mj backfires at WOT

[ComancheGurl]

Its a 4.0 FI automatic tranny

recent tune-up

Starts fine when hot or cold.

Hesitates,backfires,and sputters when accelerating in all gears.

Any thoughts?

[Geonovast]

Sounds similar to when my fuel pump was going out in my 2.5. First thing I would do is check fuel pressure.

[Darren]

Wouldn't hurt to replace the fuel filter either, it's only like $5.

 

Why did this get edited?!

[fiatslug87]

Check the EGR valve.

[dasbulliwagen]

O2 sensor could cause this too if its bad. My 2.5 would act like that sometimes while accelerating. I tried several things with the fuel system hoping to get it to go away, finally put a new O2 sensor in it just because, and as soon as I took it out on the street, it smoothed out and has been running great ever since. But like the other posters said, check the EGR valve for proper operation and closing ( it would cause a vacuum leak if it didnt close all the way), Vacuum lines, fuel pressure, fuel filter, check that the intake manifold bolts are tight... My 258 I had in My Grand Wagoneer would do this, tightening them regularly would keep things working properly. But I don't think the 4.0's had much of a problem with this. Good luck!

[carnuck]

Vacuum leak, clogged injector, water in the gas, slightly bent pushrod, bad dist cap (or incorrectly installed)

[ComancheGurl]

Took apart head and replaced a bent pushrod.

Brand new gaskets on the thing.

All vaccuum hoses have been replaced within the last 3 months.

All injectors are firing.

After installing new pushrod it still acts the same.