Occasional rough run, crazy tach, no start

[schtevo]

'94 JGC, strait 6, 255k. What's happening is this; once in awhile, regardless of speed or idle, the motor struggles to keep running, acts like it's going to die, the tachometer fluctuates wildly (although the motor isn't really revving up and down), and after 15 seconds of this, it runs fine again. There have also been several times when it's running great and suddenly just dies. I pull over, start it back up and it runs fine again. Sometimes it's hard to start. It's cranks just fine but doesn't fire at all. After a few tries it starts normally. Basicly it either runs great or barely runs at all, but never in between. This has been happening for a few months now.

My uneducated guess is that it's a spark issue. Either the plugs, cables, dist cap, coil, etc. Would these show a code if I had Autozone or somebody check it? Just seems like an arc could be the type of thing that comes and goes. Maybe I'm wrong. Suggestions?

[reekor]

Sounds like a classic crankshaft position sensor problem.

Originally Posted by schtevo

'94 JGC, strait 6, 255k. What's happening is this; once in awhile, regardless of speed or idle, the motor struggles to keep running, acts like it's going to die, the tachometer fluctuates wildly (although the motor isn't really revving up and down), and after 15 seconds of this, it runs fine again. There have also been several times when it's running great and suddenly just dies. I pull over, start it back up and it runs fine again. Sometimes it's hard to start. It's cranks just fine but doesn't fire at all. After a few tries it starts normally. Basicly it either runs great or barely runs at all, but never in between. This has been happening for a few months now.

My uneducated guess is that it's a spark issue. Either the plugs, cables, dist cap, coil, etc. Would these show a code if I had Autozone or somebody check it? Just seems like an arc could be the type of thing that comes and goes. Maybe I'm wrong. Suggestions?

[fredjacksonsan]

That's classic for the Crankshaft Position Sensor. Do a search, there are many threads about it, both here and in the Cherokee section.

Easy repair, couple hours and a $90 part.

[pkellymc]

CPS gets my vote.

[gatoratoy227]

your crankshaft position sensor is going (if not allready there) sour. the worst thing about replacing it is the clearence issues. you're going to need about 3-4 feet of extentions for your ratchet, and depending on ourdriveline set up, some times more,for my 93' cherokee sport i needed 6 feet of ratchet and exention to get at it. fun fun