new guy here, have a stock 1999 xj 4.0, auto.w/122,000 miles that has developed an issue i haven't found in forums. driving down the road motor will just die- speed doesn't matter- put in neutral, turn to off, turn key to start, & off I go!! Well yesterday, died & would not restart, got a friend to drag me home, about 2 miles, hit key in driveway, darn thing started right up. have read about issues w/crank sensor, cam sensor, etc. but not sure where to start- don't want to start throwing parts at it I don't need. any ideas, suggestions would be appreciated.

 

No codes?

Can you idle it in the driveway and reproduce the problem (in other words, run it for 20-30 minutes to get it to heat up and presumably trigger the dying)?

First of all do the requisite ground cleaning/tightening and checking of connectors.

What I would do is get a fuel pressure tester loaner tool and check that and also I'd go through and test the cam sensor and CPS to the best that can be done. If nothing jumps out, then I'd say it might be worth it to load just a new Mopar CPS into the parts cannon since those suckers seem to especially prone to thermal failure.

 

Mind did that, new crank shaft sensor fixed it

 

Crankshaft position sensor is certainly a primary suspect here.

I agree checking for codes / pending codes would be job #1 here.

Is this the original crank sensor with 122K? If so, in the absence of codes or any other smoking guns, then replacing it would be a good idea. The #1 piece of hardware that experiences thermal failure on the 4.0 is the crank sensor. #2 is the ignition coil. You can test both of them but you would have to test them while in failure mode as if the vehicle starts and runs, testing will almost assuredly yield normal results.

If you do end up replacing it, do yourself a favor and buy a genuine Mopar crank sensor. Aftermarket crank sensors are "hit and miss" (with a lot of miss).

 

Jeep shows no codes, no CEL, & as far as I know is all original. bought last year & has been great up till now. am 45 miles away from dealership for parts, so will crank up the old Harley & make a trip to the --ity!! To tjwalker, my first car in 1966 was a 1948 ****** sedan delivery- no side windows, w/Studebaker flathead 6, three on the tree & 2 wheel drive. God what a TANK, wish I still had it!!!!

 

It may be hard to find the part at a local dealership. You can find them online, though rumor has it that they're getting harder to find these days.
Call them before making the trip and make sure they have it in hand if you go that route.

 

I have heard the same thing; can be hard to source a Mopar crank sensor. Call around before firing up that Harley!

Yea, my 49 ****** was a tank too. Dang that sheet metal was thick! My ****** had a Buick engine in it which made it easy to work on. Geared to go straight up the side of a wall.....

 

Hey guy's, thanks for all the input!! found part at Denver Dodge dealer- god I hate to go to the s-ity. We live @ 8800 feet & back up to a 3000 acre ranch- it's so very peace full, but will put on my game face & do battle with all the cityidiots!!!! thanks again, Mike

 

Geez I think we are rushing to judgement here a bit on the CKPS, The usual for one of those is it wont START after shutting off, not that the thing dies while driving. Have we checked fuel pressure?
He aint gonna be happy driving a bike 100 mi to the stealership and buying and installing a ckps that he dont need.
Then again, the rule of thumb is if the ckps has never been changed, it will need to be...

 

I wonder if that rule of thumb is specific to automatics. Between myself and my dad we put over 700k on 2 different manual Jeeps, both DD's for no less than 14 years and never once replaced a CPS. Then considering that an auto has cooling lines through the radiator and the sticks don't, it seems logical that the auto tranny generates a lot more heat and hence a lot of failing CPS's.

Of course, now that I say that I'm sure my CPS will fail right after I just had the tranny out (and easy access to it) in order to replace the clutch.

Edit - I have seen several posts about the CPS failure causing stalling while driving and folks having to wait 20-30 minutes for it to cool down and then it starts right up again. The O.P. was advised by someone, <cough cough>, to start with a fuel pressure test.

 

I had this happen to 3 90s dodge dakotas. Problem always turned out being the ECU. Take your ecu off and look at the back of it and make sure it is still sealed and water tight. Make sure the gel backing is not weather checked. If it is then I would replace the ECU.

 

ok, so made trip to Denver, got part @ nearest Dodge stealership-$96.00!!!! only took 1/2 hour to r&r, then it started raining. gonna wait till weather clears- probably Tues.- don't want to tow in rain storm if problem not fixed. we are in our "mud season" now, which is great after no snow this winter. will post results asap! thanks again for input, Mike

 

Are Crown crank sensors any good? Hard to find Mopar over here...
thanks.

 

I don't know specifically, Morat, but if it were me, I'd keep looking for a Mopar (NGK) unit.

 

sorry for taking so long to get back, getting OLD ain't easy. so replaced cps, & have made several trips to Denver with no issues!! jeep is running great & is reliable again. I did see on last post that Dodge part is a NGK- dealer sold me a BDW part! hope I didn't get hosed !! we'll see how long it lasts. Thanks again for all the info & suggestions, Mike- now "time to go fishing" !!!!!