TJ 4.0 cuts out around 3k RPM...Fuel Pump???

[Boludo]

Update for the day....This morning I drove the same uphill stretch of freeway....70 to 75 MPH in 5th gear. I accelerated hard through the gears, shifting around 4000 RPM and no cut out. It ran normal. The only difference was a new tank of gas this morning. Maybe I had some bad gas....errr....my Jeep had some bad gas I mean. If so, it was really bad. We'll see what happens tomorrow.

 

[Bart]

If it comes back I'd say it's your cat or muffler. Could be a big flake the sometimes blocks the flow.

 

[BOB-CAT]

Bad Gas cap?

 

[NoTrax]

Changed my CPS when mine had the symptoms close to what your saying, but mine would just straight out DIE on the freeway.

 

[Boludo]

My wife's car did the same until I replaced the CPS....totally died with no warning. My jeep never died, just cut out, but so far I'm back to normal. Whatever is was, is has fixed itself.

 

[X1994J]

Sounds exactly like what mine did when the distributor came loose after some hard wheeling. Did you check your hold down bolt on the distributor to make sure it is tight? It was also intermittent, came and went until I figured out what it was, and ran great until I got it up in the 3K range.

 

[Boludo]

Nope, I didn't check that, but I will. Good point. Thanks.

Sounds exactly like what mine did when the distributor came loose after some hard wheeling. Did you check your hold down bolt on the distributor to make sure it is tight? It was also intermittent, came and went until I figured out what it was, and ran great until I got it up in the 3K range.

 

[JPTHING]

Crazy I was just posting about my 4.0 which runs like crap until 3k rpm then takes off like a rocket.

 

[Boludo]

Well, it wasn't a gas problem. It cut on me again yesterday after about a week of no problems. It felt a little sluggish too, but not as bad as before. Haven't checked the distributor yet, but will.

 

[rholbrook]

My money is on the CAT. Same symptoms on my TJ. The insides rot out and then as you get more RPMs going it actually pushes the insides back and blocks the exit. If you listened to it while someone actually reved the motor, you could actually hear that it was plugged. Mine had 115K miles on it.

 

[BOB-CAT]

It probably only happens when it is 1/2 full of fuel or under

 

[Boludo]

Yeah, now that you mention it, that does seem to be the case. Why would the amount of gas in the tank affect this?

It probably only happens when it is 1/2 full of fuel or under

 

[BOB-CAT]

I would bet that you have a bad gas cap or a small crack in the fuel line and it is sucking air causing the problem. Most cars today will set a code or run bad without a cap when the fuel is low in the tank.

 

[Jared]

I had a similar power problem on a 1991 4.0L XJ. The rubber hose from the fuel pump to the hard line inside the fuel tank had cracked. It would not build enough fuel pressure to feed the engine at high engine speed and under load, but it ran great with mild throttle and lower engine speed. It took quite a while to find that one... fuel pressure measured just fine unless you were hard on the throttle.

Good luck!

 

[Boludo]

Wow....so here is what it could very well be then....Last summer I dropped the gas tank to replace the pump (with a used one). I put it all back together and on my next fill up I found that I didn't get the big nut, that mounts the fuel pump, tight enough and gas leaked out when the tank got full. I found that if I don't put in more gas, and over fill it after the pump stops, then it won't leak. I have never had time to drop the tank again to tighten it up....dumb, I know. It never gave me any issues til now. Looks like I will be dropping it again soon. Time for a Jeep day. And I will probably replace the cat and muffler too.

Cracked hose inside the tank??.....I bet it took a while to find that one. I'm impressed that you did. I never would have thought of that.

Thanks for all the help and suggestions from everyone. Much appreciated!