Hey all....i got a 97 xj sport...4.0 automatic. 3 weeks ago....i started getting a week start and lumpy idle. I removed the throttle body and cleaned it. Replaced the gasket and Iac. Worked great for a few days...then it started a low rpm lumpy start about every fourth start. Until yesterday. It wouldnt start unless i had my foot on the gas...if not it would stumble and die. So this morning i replaced cap...rotor...plugs...and wires cuz they needed it anyway. First start was great. Second start...again lumpy and weak and had to have foot on gas. 3rd and 4th starts were great. Its throwing no engine codes...fuel pressure is in spec.....im clueless...any ideas???

 

Might try to pull and clean your CTS (coolant temp sensor).

 

Surprised its not throwing any codes.
Have you done the basics, plugs, distributor cap, etc.?

Could also be a vacuum leak somewhere.

 

i cleaned the throttle body a few weeks ago...iac is new. Replaced distributor cap...rotor...plugs and wires today...i checked fuel pressure...it was at a solid 46psi...so thats in spec. Once it starts it runs perfectly fine...no hesitation and good idle. Just about every fourth or fifth start it will spit and sputter and idle very low for a few seconds ( 250ish rpms ) then picks up to normal. And once about every 12 start cycles it wont start unless i put my foot on the gas pedal and keep it there. If not it will spit and sputter and die. However if i keep my foot on the gas pedal til it gets to opperating temperature i can let off the gas pedal and then its fine...it will drive perfectly fine. It is just an occasional start up issue.

 

CPS is a suspect, as is the CPS.




Wait.... what?


Your Crankshaft Positioning Sensor (located on the bell housing) and your Cam Positioning Sensor (located in the distributor) are both suspect. There are test procedures around here somewhere.

Yeah, I know. Two different things with the same abbreviation. Some people write the Crank sensor as CkPS to make it clear. Makes sense to me. It would be nice if we would all do that. Then there wouldn't be any confusion.

The Cam sensor can be inspected visually, too. Just pop the distributor cap and you'll figure it out. If it looks like it's been hitting something, you may need a new distributor. If the bushings get worn badly enough the sensor can get hit, and things don't go well from there. If there's any sign of contact, you have a problem.

 

i inspected visually the cam sensor yesterday when i replaced my cap and rotor. I couldn't see any signs of damage. I was curious if the crank sensor could be my culprit? Ive replaced it before a few years ago. Mechanically im pretty good. Not so much with electrical though....ill try to find how to test it and see what i find. I will say....generally if im gonna get a bad start its when the xj has been sitting and thd engine is cool. When its warm...it starts good for me.

 

i found then info how to check the crank sensor...i checked between pins b and c and it read open...which is what i saw it should be...so im guessing the crank sensor is good. Could the coil be bad? I replaced it a few years ago...about 15k miles ago.

 

I fought this for a while a few years ago. I changed the distributor and coil (both had 200k on them anyway), since my Crank Sensor tested OK.


Still had the same problem pop up a few days later. I had put in bigger cables, new grounds, etc...


Long story short- I ponied up and bought a Chrysler factory crank sensor and dropped it in. Worst case scenario? I have an extra.


That was 2 years ago- not a hiccup or a miss since then.


Always guess Crank Sensor. Always. $0.02

 

Bingo. If there is one sensor on a Cherokee that should never be anything but OEM, it's the crank sensor.

Testing good and operating bad is S.O.P, for aftermarket CPSs.

NTK/NGK is the only thing you should use.

 

Well...i went ahead and replaced the coil tonight....ill see how it acts between now and this weekend. If i get another bad start ill replace the crank sensor this weekend.

 

Check that connector to the coil, too.

 

Well....after replacing the coil and a few days of no problems...i had a bad start this morning after getting gas. I went and got a crank sensor and will replace it after the xj cools down. Ill check back in after i replace it

 

Well i replaced the crank sensor Saturday....so far so good.

 

Also, a weak start with low idle that dies unless you stand on the gas pedal is a classic XJ symptom for low system voltage during startup. The low voltage causes the computer to basically recycle itself. If the low voltage is a transient problem, sometimes it will pick itself up and being running/idling normally.

It may not be obvious, but your starter and/or battery, and/or connections between them may be dragging the system voltage down when you crank to start. With the vehicle running, go visit an auto parts store and have the battery, starter, charging system tested (they normally do this for free). If the system isn't maintaining sufficient voltage during the start, their test will usually catch that.