So heres the story. I have a 2001 4.0L swapped into my 84 cj-8.

Started a while ago just stuttering once in a while going down the highway (slightly annoying but not critical)

Starting about last Memorial day at Rubicon it started loading up at low rpm's, If I revved it up it would clear out and run normal. (this is where I first noticed the loss of power) Also, in neutral it revs up fine all the way to red line......but when in gear going down the road it is slow, and won't rev past three grand.....and won't kick the trans down.

Over the summer it started not wanting to start when hot (almost like it was flooding, again I revved it up and it would clear out), I noticed a large drop in power and started sucking down gas around town. It threw a code for multiple cylinder misfire which told me injectors or 02 sensors...replaced injectors and o2 sensors with no improvement.

I took it to a shop where they tested sensors (seemed to be operating within tolerances) they also noted the sluggishness but couldn't reproduce the hard starting or stumbling. They seemed to think the only option left was the computer. But couldn't figure it out for sure.

Any Ideas??? I am lost!
~Robert

P.S. I am stuck in a borrowed minivan until I get my jeep running right, HELP!

Maybe the cam position sensor had mine go out last year and seems like similar symptoms

X2 on the cam position sensor. i had similar issues with mine and once i replaced the sensor it was all good.

I had a similar problem with my wife's 2001 Cherokee. It was under warranty and the dealer went round and round with it. I ending up isolating the problem myself and demanding an engine replacement. When the engine was hot and you went to start it it would stumble and then clear up when you revved it. It was leaking small amounts of coolant into the cylinder when hot and under pressure due to a warped block and head. How's your oil pressure? Mine was a little low when hot due to excessive bearing wear caused by the warped block. You may want to get it hot and pull the plugs and inspect for coolant. I had none in my oil and it was almost unnoticable amounts missing from the resovoir. I only found it in the cylinder. It also threw the codes for the multiple cylinder misfire. One of the first things the dealer did was put heat shields under the fuel rail and around the injectors. Apparently there was problem with heat causing fuel vaporization in the rail before the injectors. This was not my problem but according the the Jeep tech had been causing the same symptoms in others.

Im having similar problems with mine right now. My system started fumbling the first Day I arrived in Farmington NM(5800 Ft elevation). My jeep was originally sitten at 1800 FT in Barstow CA. I got sick of it, and ended up dropping the Jeep off at the local Community College. There is a Guru up their that is a instructor and specializes in Forced induction. Anyways, He called me back and told me I had a bad MAP sensor! He replaced it with a factory 1 BAR MAP and the jeep idles fine and is crisp in throttle response. I hope this helps out any one else out there. He will take it for a drive and see how the system responds to boost on a 1 BAR MAP. This will be interesting.

My dad was having the same problem with his Cherokee. He changed the CPS but it was still having problems with it stumbling so he decided to change the fuel pump. It fired right up and is running perfect now with no hesitation or stumbling. You might want to check your fuel pressure if you haven't already.

Is there a way to test the CPS or Map sensor? Had a fuel pressure gauge in line...45-50psi running.

intake gaskets.... spray flammable brake cleaner where the intake meets the head with the motor running if you hear a change in how it runs then change the gaskets and be done with it. be sure to spray underneath the intake too because that is where the gaskets usually fain due to the heat of the exhaust manifold. i would bet a pretty penny that is what it is due to the multiple cylinder misfire sucking to much air into the cylinder.

Thanks, I have not had a chance to work on it yet but as soon as its running well I'll post up............if not I'll be back for more i-dee-errrrrs.

I just had the exact same symptoms in my YJ. I swapped in a used fuel tank last week , it still had the fuel pump/sending unit in it so I though I would keep my old one as a spare. The first couple of days driving around seemed just fine. Then I started to notice lack of power/ sputtering/surging etc.. only after driving for 30mins or so. Same thing if I revved through it , it got better (sometimes). Gradually got worse.
I could hear the fuel pump come on before starting and pressure at the rail was good too, but I still figured it must be the fuel pump or I pinched a line when installing the gas tank, dropped the tank a bit checked the fuel lines, all ok. I kept the fuel pump from my old tank, so I ended up swapping it out , now my Jeep feels like new again. Wooohooo.
I guess the pump was just getting tired and was giving up after running for a while.

PS I cut an access hatch in my rear floor above the fuel pump. Makes it really easy to swap out the unit ( dont have to drop the tank ).

HTH
Rob

update... still not working...Top

My speedo sensor was going out and it did the same thing... Just thowing that out there.

Reproduce the no start when hot issue, and then run a compression test...that'll tell you whether or not the head gasket is on its way out.

had similar problems with mine...rebuilt the head and replaced the gasket...no symptoms yet...knock on wood

OK here is a weird condition for your problem..
Check your fuel tank pressure by releasing your gas cap when it starts stumbling. I have a Mopar kit on my 4.2 and with the stock tank it builds gobs of heat/pressure due to the return fuel line on the 4.0 EFI. Your conversion may be having the same issue with the stock tank if your still running it.

I ended up removing the little gasket at the gas cap and it hasn't happened since. Not the safest thing but it works for some reason.

had a similar problem when I got a little water in my intake... ended up being the Throttle position sensor in the throttle body.

Thanks for the help amigos, Turns out it was the fuel pump.........the old one sucked up some shit from the tank, from a shitty gas station ( ie metal shavings and formagasket) dropped the fuel pressure to 20-30 psi