88 Jeep Cherokee - 4.0L

Been running great, suddenly one day it would not start. Did all the normal stuff, plugs, rotor, coil, blah blah blah... still no start. Cranks, but no start. I took out one of the spark plugs and cranked it for fun... it started. Ran fine the rest of the day even when I shut it off and restarted it. Next day no start. Tried the plug trick again. NO start. Pulled a random vacuum hose. Started. RAn fine for a day or two... then one day... no start. Started disconnecting things at random and trying to start with them disconnected: idle speed stepper motor worked once not repeatable - spark plug removed works sporadically, MAP disconnected works sporadically, vacuum hoses work sporadically. ONe day I just insulted it's manhood... it worked, not repeatable.

Once I do get it started it will run fine for the rest of a given day and occasionally for a day or two after that. Then it won't start again and I have to go through a whole series of the above listed steps to see which one will start it today. I am thinking about replacing parts starting with the idle speed stepper motor until something fixes it permanently. Was hoping someone smarter than me could point me in the right direction before I rebuild my engine one piece at a time.

88 Jeep Cherokee - 4.0L

Been running great, suddenly one day it would not start. Did all the normal stuff, plugs, rotor, coil, blah blah blah... still no start. Cranks, but no start. I took out one of the spark plugs and cranked it for fun... it started. Ran fine the rest of the day even when I shut it off and restarted it. Next day no start. Tried the plug trick again. NO start. Pulled a random vacuum hose. Started. RAn fine for a day or two... then one day... no start. Started disconnecting things at random and trying to start with them disconnected: idle speed stepper motor worked once not repeatable - spark plug removed works sporadically, MAP disconnected works sporadically, vacuum hoses work sporadically. ONe day I just insulted it's manhood... it worked, not repeatable.

Once I do get it started it will run fine for the rest of a given day and occasionally for a day or two after that. Then it won't start again and I have to go through a whole series of the above listed steps to see which one will start it today. I am thinking about replacing parts starting with the idle speed stepper motor until something fixes it permanently. Was hoping someone smarter than me could point me in the right direction before I rebuild my engine one piece at a time.


Have you checked for spark when it won't start. Next time check for spark at the coil wire , if you have spark at coil wire . Remove one of the plug wires and check for spark. holler at jeepman600@aol.com
dale If you know where the wire connector for the crankshaft sensor is try unplugging and replugging it, see if it starts. Its at the fuel rail, back at firewall drivers side , oval connector with three wires . It's hooked on a small bracket of fuel rail. Have pics. if you need can't send thru forum. :2cents:

Hey Dale,

Thanks for the reply. I have been out crawling all over that thing for the last couple hours. I read an old thread about the crankshaft position sensor and went looking for it. I am not sure I found the sensor, but I found a set of wires leading from the wiring harness down toward the transmission. As I followed them I found a plastic connector that connected the wires form the harness to wires that went to the top of the transmission. As I was looking at them I noted that the plastic connector was dangerously close to part of the exhaust manifold. When I pulled them away.... I'm sure you know what I saw. I don't know if they go to the CPS or not but I am guessing they are part of the problem. If they do go to the CSP I have no idea how to reach it other than dropping the transmission.

Anyway... I appreciate your reply and I'll let you know what I come up with. Once I get the connector replaced, I'll try the checks you suggested.

the crank sensor bolts are 11mm, you have to get at it from under the jeep, drivers side, it helps if you remove the down shift cable and bracket, then you need universal on the socket, with extensions, just don't drop a bolt in the bellhousing....

Hey Dale,

Thanks for the reply. I have been out crawling all over that thing for the last couple hours. I read an old thread about the crankshaft position sensor and went looking for it. I am not sure I found the sensor, but I found a set of wires leading from the wiring harness down toward the transmission. As I followed them I found a plastic connector that connected the wires form the harness to wires that went to the top of the transmission. As I was looking at them I noted that the plastic connector was dangerously close to part of the exhaust manifold. When I pulled them away.... I'm sure you know what I saw. I don't know if they go to the CPS or not but I am guessing they are part of the problem. If they do go to the CSP I have no idea how to reach it other than dropping the transmission.

Anyway... I appreciate your reply and I'll let you know what I come up with. Once I get the connector replaced, I'll try the checks you suggested.


Sounds like you found the sensor, if you email me direct i'll be glad to send info on removal & installing it. Ive got pics. if you need. The hareness runs close to manifold exhaust. I always use plastic wire ties to tie it up high from the heat and exhaust. Heat really takes toll on the sensors. You don't have to drop the transmission. Ive changed them in 15-20 min with no problems. Questions holler jeepman600@aol.com Dale