XJ died going down highway.

[MisterFubar]

99XJ 4.0L AW4 96K

I was cruising along at about 70 and it bucked a couple times, backfired and lost all power. I put it in neutral as I was rolling to a stop and it died. I threw it in park and it fired right up and idled fine, so I continued on to where I was going. A couple hours later I was driving home and it did the same thing, I couldn't give it any gas without it stumbling and cutting out. I pulled over, let it sit(still running) for about 30 seconds and continued my drive home without any other problems. I was monitoring the TPS, Map, Timing, and Fuel flow with my Scangauge and nothing looked out of the ordinary when it was acting up. It didn't seem to have any problems until it was good and hot. On the trip home I had my fuel pressure gauge taped to the windshield and fuel pressure stayed at 50 +/-2 PSI. What the hell is wrong with this thing now?

A little history on it... A few weeks ago I had a bucking/surging problem under throttle that was fixed with an IAC.(the details of that can be found here http://www.naxja.org/forum/showthread.php?t=926165 ) A week ago I had some hesitation when it was first switching into closed loop mode that would sometimes throw a code P0135. That was fixed with an upstream 02 sensor(along with a header, a new cat, and a catback) It had been running fine all week during the same drive in basically the same conditions and I would like to think this is a new problem.


Work that's been done/parts that have been replaced.
Exhaust manifold replaced with header
New Cat
New up and downstream O2 Sensors
New IAC
New Cap/rotor/plugs/coil
New muffler and tailpipe
New Crank Position Sensor
Grounds Cleaned/replaced
Fuel injectors heat wrapped
Vacuum hoses checked, double checked and a few replaced.

I haven't done any troubleshooting yet on this problem with the exception of watching the scangauge and hooking up the fuel pressure gauge on my drive home.

I bought this thing hoping it would be a good Daily Driver and so far it's really been letting me down.

[JNickel101]

Sounds like Crank Sensor....but you said that is new...so....ya got me. How long ago was it replaced? And did you get one from the dealer or....?

EDIT: Did it throw any engine codes????

[Bzamora]

You described the classic signs of either a bad crank sensor or cam sensor. Also check the harness and connections.

[MisterFubar]

Originally Posted by JNickel101

Sounds like Crank Sensor....but you said that is new...so....ya got me. How long ago was it replaced? And did you get one from the dealer or....?

EDIT: Did it throw any engine codes????

The crank sensor is 2 weeks old and it's a Borg Warner. I may take it up to the parts store and swap it out for a new one and have them order a distributor pick-up(cam sensor). It hasn't thrown any codes.

[MisterFubar]

Picked up the Cam sensor they ordered for me and took it out to the parking lot to install... wrong sensor, it was a little smaller and wouldn't fit in the distributor right and the bolt holes didn't line up. Took the old one into the store and crossed the Chrysler number on it and it came up with the one that they sold me... The box was a little beat up so they are thinking it might have got switched with another one at some point, and have another one coming in for me tonight...

If it wasn't for bad luck I wouldn't have any luck at all.

[Runnin'OnEmpty]

Yeah the cam sensor has to be matched to the distributor number; there were two different types for the HO engines. Murphy's Law states you'll always get the wrong one.....

At least they're very easy to change, and a new one should fix your problem.

Mine acted the same way when the cam sensor went out on my 96.

[MisterFubar]

Originally Posted by Runnin'OnEmpty

Yeah the cam sensor has to be matched to the distributor number; there were two different types for the HO engines. Murphy's Law states you'll always get the wrong one.....

At least they're very easy to change, and a new one should fix your problem.

Mine acted the same way when the cam sensor went out on my 96.

The one they gave me that didn't fit is the correct part number by app in the catalog and it's a direct cross off the chrysler number on the one in my Jeep... hopefully it's just boxed wrong, I'll find out tomorrow.

They are easy to change, it's about a 3 minute swap. I wish all the sensors were that easy to change.

[MisterFubar]

Got the right Cam Sensor and got it installed.

I drove my normal test loop that I was always able to duplicate the problem on twice and I never had a hiccup. looks like another problem fixed. I wonder what will break next.

[cygnus58]

did you replace the crank sensor for this same symptom/issue?
If not, i would bet you'll be back here with the same problem..

[MisterFubar]

Originally Posted by cygnus58

did you replace the crank sensor for this same symptom/issue?
If not, i would bet you'll be back here with the same problem..

The crank sensor was replaced a few weeks ago for a different issue.(just like it says in the first post)

I'm fairly positive that this issue is fixed. I was able to duplicate the problem several times and after the cam sensor was replaced I did the same drive under the same conditions and I wasn't able to duplicate it.

[XJ9888]

One thing you might want to try: if your fuel pressure guage has a bleed hose, do a volume test on your fuel pump. I had some similar problems(dying on highway when hot, bucking ect.) The guage said i had 50 psi, but it was 50 psi of vapor (when acting up). Fuel pump was the remedy.