Now at a loss! 98 4.0 Auto stumbling

Wow! Really tired of this one!
History.
Bought 3 years ago. Ran fine for 2yrs, Noticed leaking heater core. replaced.
Soon after had stumbling issues small at first then check engine light and started getting worse. Code read P0340. Replaced entire distributer as the shaft was loose along with Cam sensor. Replaced crank sensor. Still the same and sometimes P1391 Intermittent loss of cam or crank sensor. Finally took to shop yesterday and they said cap and rotor were toast! Ooops, thought I replaced that!
After they replaced cap/rotor the light came back on (P0340). They tested all circuits, wiggle test, etc. All tested good. They reset PCM and ran it for hours both idling and driving around. Ran fine for them and code didn't return.
I picked up this morning and after driving to work (about 35 min.) it started stumbling baaad, worse than ever and died as I pulled into parking lot.
Checked the cap/rotor. Both look very new. Checked fuel pressure. 49psi at start and run and doesn't "leak down" after shut off at all.
I can start and run it but will stumble and miss when I put in gear.

Any ideas, please!

Please no "use your search button" comments. This ain't my 1st rodeo!:roll:

First idea, what year? If this ain't your first rodeo you should know better.

It's in the title! 98 4.0, Auto..........:confused1

Right you are! Sorry..

It's been my experience that with p0320 and p0340 codes that the indicated circuit is the opposite of the problem sometimes. AKA the p0340 (cam) is actually implicating the crank sensor.

Did you replace it with a dealer sensor or aftermarket?

JJacobs said:

Right you are! Sorry..

It's been my experience that with p0320 and p0340 codes that the indicated circuit is the opposite of the problem sometimes. AKA the p0340 (cam) is actually implicating the crank sensor.

I'm not a big fan of chucking parts at problems, but crank sensors are a known weak point and replacing it just might fall into the 'least intrusive test' (dollars and time) category.

Click to expand...

Yeah, I know what you mean. I'm leaning that way but I just put one in in September. It was after market cheapo tho.

Any other ideas? I hate to throw money into this thing. Ready to be done with itHasta

88xjlover said:

Any other ideas? I hate to throw money into this thing. Ready to be done with itHasta

Click to expand...

test the cps and make sure the cps wiring and harness are not damaged. cheapo electronics show their value as they age.

Check the firing order? Should be 1-5-3-6-2-4. Not saying you're stupid, or that the mechanic is stupid, but it's so easy to check you may as well get it out of the way.

Start at the beginning, of course. New cap and rotor, how about the wires, plugs and coil ? Test the CKP, test the CPS, test the CTS, test the O2 sensors, clean the ground wires connections, inspect the wire harness for loose or dirty plugs, inspect the wire harness for chafed insulation causing an intermittent short circuit.

Thanks guys! I will start again on all the testing after work. It's stuck here anyway! Did check firing order and is good. Didn't have a spark plug socket yesterday here at work. brought my tools today so I'll check those to start with.

Tim_MN said:

Start at the beginning, of course. New cap and rotor, how about the wires, plugs and coil ? Test the CKP, test the CPS, test the CTS, test the O2 sensors, clean the ground wires connections, inspect the wire harness for loose or dirty plugs, inspect the wire harness for chafed insulation causing an intermittent short circuit.

Click to expand...

Cap and rotor new. Will pull plugs as noted above, all sensors tested good according to mechanic but after replacing cap and rotor it didn't have a problem for them.... Forgot my book :sure:so I'll google testing specs for coil and wires, etc.

O.k. got it home. Bad wiring on the harness before the coil. All those wires were slightly melty. pulled them all apart and wrapped the two wires for the coil. Also noticed by accident that the vacuum line on the back of the intake manifold is a little funky. I move it up or down a little and it stalls the motor. I noticed that it made the same motion when I gassed the throttle with the motor moving up and down. I secured it in a slightly different spot with a zip tie and made it home.
Black electrical tape and zip tie's. Is that McGyver or what!

Duct tape will do both jobs, and you get extra points on your Man-Card.

Curious as to what caused the melting.

joe_peters said:

Duct tape will do both jobs, and you get extra points on your Man-Card.

Curious as to what caused the melting.

Click to expand...

That part of the harness was between the distributor and the block when I replaced the dizzy. I thought it was a little strange to be there so I moved it to the outside of the dizzy. The heat damage was probably already done at that point but I didn't notice it till now. All the factory tape was hard as a rock and came off in a hundred little pieces.
Duct tape was available but when I saw the electrical tape I figured do it with the right stuff. I may have to replace that part of the harness later but it got me home!

It did have a overheating issue before I did the heater core. I never let it get very hot but maybe the extra heat of the motor melted the insulation on the wires. They were all kinda stuck together but easily pulled apart.

Gave me a miss as I was coming back from dropping my daughter off. I'll try and fix that vacuum leak tomorrow and see where it goes from there. I know you all can't wait!

88xjlover said:

Also noticed by accident that the vacuum line on the back of the intake manifold is a little funky. I move it up or down a little and it stalls the motor. I noticed that it made the same motion when I gassed the throttle with the motor moving up and down!

Click to expand...

where/what did the other end of the vacuum line go to? was it by any chance the vacuum line to the MAP sensor?

No it's the one that goes to A/C and cruise.

Sounds like a run of the mill vac leak causing uneven idle on that one.

Also, all obd II XJs have the MAP mounted directly to the side of the throttle body, so it can't be that.

If the vacuum doesn't fix the issue, the coil may be suspect. Mine was faulty as it wouldn't produce the correct voltage. This caused a miss and thus a rich condition as it didn't produce enough voltage to correctly light up the plugs. A spare in the Jeep is always a good idea. -B