Need help in troubleshooting ignition problem

but I don't know if it a PCM replacement or just an add on.>

First check the Crankcase Position Sensor. Many a jeep owner has cursed the *%$**!! who designed that stupid thing!

Next up I would replace the coil anyway. I've seen a perfectly good reading come from a coil that still won't spark. Rare, but I have seen it.

Can't think of anything else...but then again it's 4:00am (just finished putting in a new stereo in the XJ).

Drifter "I've been here, I've been there..."

Bill, do V6's have that CPS? He says he has the V6.

But other than a dead CPS, how is the body ground? If bad no spark. I test them by running a booster cable from the battery negative to the firewall. On the straight six, the ground is a wire mesh strap from the head to the firewall, don't know where it is on the V6 or V8.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"L.W.(ßill) Hughes III" wrote:

> but I don't know if it a PCM replacement or just an add on.> >

Steve should follow the advice given at the end of Bill's first URL (below) -- find the 2-wire plug for the CPS driver's side near the firewall, just behind the valve cover. Carefully unplug (don't break the keeper off), securely replug. My `89 XJ would refuse to start about once a year, curiously, usually just after an oil change. Unplug, reconnect, start up and I'd be good to go another 15,000 miles or so before it happened again. Never did have to replace the part.

L.W.(ßill) Hughes III wrote:

They get bad connections easy, some spray contact cleaner in them and dielectric grease on the seal helps. Just unplugging is still good, the pin gets scratched enough to make a new contact usually.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Lee Ayrt>

Good catch Mike. I am reasonably sure that the V6 4.0 in the 95 ZJ still has a CPS. Unfortunately the sensor itself is constructed of pure "FailureToReadTheFineManualanium" and therefore quite expensive. It is also somewhat difficult to locate, since the first problem would be locating the other cylinder bank under the hood.

Mike Romain proclaimed:

Thanks for the great help. It was the Crank Position Sensor. I purchased a replacement from AutoZone for $55. After installing it, the car cranked right up. The Crankshaft Position Sensor is not even mentioned in my Haynes Jeep repair manual. I would not have been able to fix this if it was not for the help in this group, especially L.W. ("ßill") Hughes III . I can't thank you enough. Steve Smith

I forgot to mention, I was incorrect to type "V6" in my original post. It's a I6. I realized my error right after I posted, but I figured you guys would know what I meant to type. Steve Smith

I'm still getting used to you Americans calling it an "Inline 6" instead of a "Straight 6" :-)

Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ

Dave Milne did pass the time by typing:

Well, the designation on the ZJs paperwork is L6, linear 6 I suppose.

The only issue is they now 'do' have a V6 for some of the Jeeps and Grands are their own animal....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Steve Smith wrote:

Which leads me to wonder if the problem is not the CPS, as is so often assumed, but really a fault in the computer -- some endless loop triggered when inputs line up _just_so_ or something (in my mind I'm picturing the old MS-DOS loop of "Printer not found - Abort, Retry or Fail? Abort, Retry or Fail?"). After all, the CPS is just a dumb sensor, unplugging it shouldn't fix or reset anything in it.

Which then makes me wonder how many CPS have been needlessly replaced and paid for either in cash or busted knuckles.

L.W.(Bill) Hughes III wrote:

They are computer signal pins. The socket has a point that scribes the pin every time it is plugged in. The power level is so low, the slightest amount of corrosion kills the signal, so just unplugging them gives a brand new contact via that scribe pin that will last for a bit. Same for replacing them, one half just got new.

The best is to clean them with a spray contact cleaner. WD40 will work in a pinch, but. Then sealing the plug skirt with dielectric grease also helps keep them clean.

We were told our TPS was dead 4 or 5 years ago now and all it needed was the spray clean with a fresh clean every couple years or so.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Lee Ayrt>

but I don't know if it a PCM replacement or just an add on.>