It almost acts like it's running out of gas, but it keeps going just sputters. It idles a little rough too, but then as soon as you hit the gas it clears out and runs fine up until about 55mph, it seems to chug when letting off the accelerator. Seems like a fuel-to-air ratio issue.. not sure. As soon as I put my foot into the pedal, it doesnt do it.
I've replaced the tps, cps, map sensor, plugs, plug wires, cap and rotor, Fuel filter. I've seafoamed and tried injector cleaners.
Any suggestions? Maybe an O2 sensor...

thanks

 

vacuum lines check them

 

I can't find or hear any vacuum leaks... I'll double check though.

 

it sounds like the same thing my dads truck did we took it to a auto shop and the inatially said a blown intake manifold gasket then we took it somewhere else and they hooked up one vacuum line and it work fine

 

I just had mine smoged it had a bad o2 sensor,it ran fine,just very rich.Try testing with ohm meter,my new one was about 6 ohms,also try running it unpluged to see if helps becouse if it is bad it may have faild on the lean side

 

I tried unplugging the 02 that didn't make a difference, I'm almost starting to wonder if the trany would cause that? It works 100% in all gears, but I get this terrible shudder at speeds past 55 when just trying to keep a constant speed. If I accelerate it stops or if I let off on the gass enough to start slowing down, and it only does this going faster then 55, thats what I dont get? tranny fluid looks clean and doesn't smell bad.

 

its a shutter like death wobble? or sputter like the engine is dieing

 

it sputters/shudders like the engine cuts out, almost like a back-fire, but I cant hear it. Maybe you're right about the intake??.. its weird because it doesn't do it unless past 55mph which would sounds like a death wobble, but It doesn't have the death wobble, I made sure of that. it has all new control arm and sway bar bushings up front, and leaf spring bushings in the rear. All polly urethane. And it also stops as soon as I give it gas no mater what speed, only when Im trying to keep a constant speed or letting off on the gas it does it. I dont get any weird viberations even at 65+ just the engine or now Im starting to think trans....

 

Check if it's RPM related or speed related - note your cruise RPM at 55mph, then shift into third. Get to the same crankshaft speed, and see if the problem recurs.

Then, get up to 55mph and see if it recurs.

If it's engine speed related, check your TPS function and see if there's a "flat spot" (check the sweep of the thing using an analogue ohmmeter - the test in the manual simply verifies adjustment.) If it's vehicle speed related, check from the driveshaft on back.

 

Sounds good, I'll try all that. Note the TPS is brand new, but I will check it anyway. Also when it's sputtering-out, I don't see either the speedo or tach moving at all. Any ideas what to look for on the driveshaft back? Also wouild an IAC cause something like that on highway speeds? It does have a bit of a idle problem, but once it's warmed up, it goes away.

 

I would do the fuel pressure test at the test port on the fuel injection rail. It's a very easy test that takes about 5 minutes and you can rule out or identify a bad fuel pump or fuel pressure regulator.

Hook a pressure guage up to the test port. Start the Jeep. You should have 30+-1 PSI. Anything lower is a bad Fuel Pump. If the pressure is good at that point. Then, remove the vacuum line form the Fuel pressure regulator at the front of the fuel injection rail. You should now have 39+-1 PSI. Anything else and your fuel pressure regulator is bad.

 

That sounds like a good idea. I'll work on that too. Would the jeep still drive fine under highway speeds if one of those were bad?

 

Sure. The fuel pump usually goes bad gradually rather than just quitting. Your Jeep starts stumbling under acceleration and when pulling hills, first. Then, after a period of that it will just quit.

 

I've been through a few TPS units (got up to 5 RENIX XJs once...) and I did have a faulty one out of the box. Fortunately, I'm in the habit of checking things like that before I put them anywhere near a vehicle...

 

I still haven't solved the problem and it seems to be getting worse. However the pressure regulator and pump are good along with the tps. Now I notice it happening at all speeds but mostly still hwy. I can actaully see the tach dropping rpms when it does it. I have a bad feeling about this. think it's tranny related or possibly the rear diff. I'm clueless.