88 XJ 4.0 random stall and no start

[SoCal88XJ]

Hey everybody, long time no see. My $200 XJ had been such a great vehicle that I rarely need to do anything except regular maintenance. However, it has developed an annoying problem which comes and goes but lately has been happening more frequently. It started as a random wont start issue, where the engine would crank over yet never even try and start. If the vehicle was left alone, it would eventually start normally and run fine for days. One day while digging around the engine compartment looking for bad wires, I discovered that wiggling the wiring harness near the drivers side firewall would temprarily fix the problem. An even closer inspection shows the wire from the crank position sensor runs very close to the exhaust manifold and had a surface burn. I later found that wiggling this wire would immediately solve the no start issue. Because it happened once a month or so, I ignored replacing it as a future task to be completed. This week, the truck started shutting off while driving which never happened before. At first it was a hiccup and later turned into a stall. Once stalled it is simply cranks over with no catch, the smell of fuel in the exhaust and sometimes a momentary start then stop. I noticed that the tach immediatly snaps to 0 rpm just like the key is shut off long before the engine finishes spooling down. Wiggling the crank position sensor wire doenst seem to have any effect on this. If I leave it for 15 minutes, it starts right back up as if there was no problem. Sometimes if I cycle the key switch on/off a bunch of times I can get the truck to start for a moment as normal then it just shuts back off. I can hear the fuel pump, smell gas out the exhaust and purge gas from the FI stem. My search on this site shows that the CPS might be the culprit but does this sound like how it acts when it goes out? Thanks for your help, I'm trying to get a CPS as a replacement now if only to fix what I should have done a while ago. I hate intermittent problems, sooo much harder to track down.

 

[CJR]

SoCal88XJ,

The Renix XJs are notorious for connectors that make bad contacts between the pins. Sounds like your CPS is either intermittenly bad or is just making poor contact in the connector. I'd suggest cleaning the CPS connector real well and then coating the pins with some Deoxit(available at Radio Shack). See if that helps? If not, then the CPS is defective. Without a properly working CPS the engine typically dies. For some reason, in this time frame of Jeeps, the materials used in the connector pins was terrible. My son's FSJ had a connector that was always green with corrosion. No matter how well we cleaned it, a week later it was green again.

Best regards,

CJR

 

[scca28]

I had the exact same situation with my '88. Word for word, in fact I had to look back up top at the name to see if I wasn't the original poster! Anyway, when I had my engine out for the swapover, I replaced every connector I could get my hands on. Got the parts from a guy on Ebay. He sold the pins seperate from the plastic housings, most of mine had the lock tabs broken from age. All of the new pins are crimped onto the wires and backed up with a touch of solder for good measure. The new housings snap together nicely and come with new rubber seals. Now, it's been a couple of months since the new engine, and there are still times when I brace myself for the stuttering or stalling, and it dosen't happen at all! Eventually I'll get used to it running so well...
Aside from that, if you are running on the original CPS, I'd still recommend replacing that anyway.

 

[SoCal88XJ]

Excellent, it sounds like I'm on the right track. I drove home to the truck at lunch just to take a look at the plug on the CPS. The plug was in pristine shape and still greased. Unfortunately, I couldn't get it to "not start" so I could check for continuity. I'm sure if I put the trailer on it and start towing into a busy intersection it will immediately fail as it did twice yesterday!!! Either way, I have the part on order. Thanks for all your help, I'll post back with my findings for good measure!

 

[SoCal88XJ]

As a note, ever since I inspected that crank position sensor plug the problem has vanished. While mine looks as good as you might expect, it seems it still may have been the source of my issues. Thanks for everyones posts, this site really has a good community with a lot of eyes! Got to love the XJ!

 

[SoCal88XJ]

FOLLOW UP: As it turned out the entire problem was from my coil/module. The connectors under the coil to the module are exposed to the elements and mine had become corroded with dirt. This was an easy problem to reproduce if the truck is intermittently running. While running, tap on the coil with the blunt end of a screwdriver and the truck would stall. Two torx screws hold the coil to the module. Clean the connectors and rebend to an arc. Easy free fix!