PLEASE HELP... engine studders

[bowmans86mj]

i have a weird studder at low RPM's but seems to get better when warmed up. i got new wires plugs cap and rotor all in already. i did recently undo the front axle vacuum lines to fix the 4x4 and did not re apply them is that possibly the prob???.. PLEASE HELP! :wall:

[Geonovast]

It can't be those vacuum lines. They're not part of the engine's vacuum system, they operated off Transfercase vacuum.

 

A likely cause could be a dying CPS.

[bowmans86mj]

what exactly is that and whats the cost for one

[Geonovast]

CPS is the Crank Position Sensor. It's a magnetic pickup bolted to the top of the bellhousing, on the driver's side. It reads teeth on the flywheel so it knows when to tell the coil to fire. If it's dying, it may not read fast enough every time, causing late firing.

 

It may just need to be cleaned up.

 

I believe new ones run about $60-$70, but you might be able to find a used one for much cheaper. I believe you can get one from any 86-90 2.5L or 87-90 4.0L

[jpdocdave]

crank sensor is usually a no start, or stutters then dies w/ a no start for a short time. and it difenatly could be a vacuum leak, especially at low rpms are when they show up, i've never heard of the disconnect using t case vacuum. it usually runs right to a vacuum canister that is supplied by the engine vacuum in my expereince, and if there is an open vacuum line from there it can cause this sort of problem.

 

if those vacuum lines are just hangin still, to make it simple just plug them all up, and see if it helps.

[bowmans86mj]

will do and also can anyone get a pic of where that sensor is located?? cause i can't find one good enough to c it

[Geonovast]

It isn't likely, but a Dying CPS can cause those symptoms.

 

Hm.. I thought the T-case/CAD vacuum was a separate system. I'll have to examine the XJ tomorrow to see what's going on under there.

[jpdocdave]

It isn't likely, but a Dying CPS can cause those symptoms.

 

Hm.. I thought the T-case/CAD vacuum was a separate system. I'll have to examine the XJ tomorrow to see what's going on under there.

 

i could be wrong to, i have been lucky enough to avoid that stupid system most of my life. my jeeps that have it have always worked. but i thought i've heard of people taking it out of play, and leaving a vacuum line open off the engine.

[bowmans86mj]

plugged the lines and she purs like a kitten again... thank you for the help

[jpdocdave]

good, thanks for posting the fix, i guess that confirms i wasn't crazy that the vacuum is supplied by the engine.

[bowmans86mj]

yeah.. well looking the vacuum lines actually hook up to metal lines similar to brake lines and run up the fire wall or close to it.. but again. yes it did work and thank you for all the help