Jeep dying...help?

Dirty Wop · Jun 7, 2006

So I am driving down the road the other day and approaching a stop sign. Shortly before I reach it as I am braking the engine dies. Nothing electrical, just all of a sudden the engine stops. I come to a stop and try to restart it, starts up just fine, but immediatly revs to about 3000rpms for about 6 seconds and then drops down to its normal idle and runs fine. This has happened a few times to me.

It's a 91 XJ 4.0L I6 HO.

Details:
-Only happens when I am slowing down, or at slow speeds and not on the pedal
-I know that the PCV valves are bad and I have some oil in the air filter (fixing all that tonight

)

Any help would be greatly appreciated.

Toyoda1 · Jun 7, 2006

Ive seen similar problems on non-Jeeps and it has been the idle air control valve. Hard to say without actually looking at it, but its possible thats it.

yjkrawlin · Jun 7, 2006

ive had the high idle thing happen if the jeep dies on the trail, i just assumed that it was the excess fuel dumped that the computer was compisating for

Dirty Wop · Jun 7, 2006

yjkrawlin said:
ive had the high idle thing happen if the jeep dies on the trail, i just assumed that it was the excess fuel dumped that the computer was compisating for

I can understand that, but what would cause it to die in the first place?

KarlVP · Jun 7, 2006

My renix XJ used to do that all the time too. I never really solved the problem 100%. I did clean out the computer contacts. Replaced the TPS and IAC.

Try cleaning your throttle plate. As for the revving, push your gas pedal all the way to the floor for three seconds with the engine off. Then re-start.

That seemed to happen on my XJ only when making short "errand trips" around town. The highway trips didn't seem to bother it.

More info can be found by hitting up www.naxja.org and using thier search feature. They will crucify your ass if you post the question straight up, so many people ask it there, it makes thier blood boil.

yjkrawlin · Jun 7, 2006

when i first bought my jeep, it did the same thing, but would have a hard time starting back up(sorry just remembered, it was while ago) it wound up being just the cap and rotor/ plugs where worn out

yjkrawlin · Jun 7, 2006

can you run the codes on xjs like a yj or a tj, with the ign. switch?

NotMatt · Jun 7, 2006

Crank Position Sensor is a common cause for this problem. First thing I would do is unplug the connector and look to see if you've got any corrosion or moisture in there. Clean it will and put some dielectric grease in and hook things back up and see if the problem goes away.

The CPS connector is pretty easy to find, it's on the driver's side on top of the intake manifold near the firewall. You'll have to trace the wires to find the one that goes down to the bellhousing. On a '91 it should be a round-ish connector just sitting there basically.

Dirty Wop · Jun 7, 2006

Thanks guys...I will give it a shot tonight and let ya know how it works.

KarlVP · Jun 7, 2006

NotMatt said:
Crank Position Sensor is a common cause for this problem. First thing I would do is unplug the connector and look to see if you've got any corrosion or moisture in there. Clean it will and put some dielectric grease in and hook things back up and see if the problem goes away.

The CPS connector is pretty easy to find, it's on the driver's side on top of the intake manifold near the firewall. You'll have to trace the wires to find the one that goes down to the bellhousing. On a '91 it should be a round-ish connector just sitting there basically.

If the CPS were going, it may have a "it's not starting at all" symptom.

NotMatt · Jun 7, 2006

KarlVP said:
If the CPS were going, it may have a "it's not starting at all" symptom.

Yes, if the CPS is just plain bad, it will do the "no start at all" thing... but it can also just simply cut in and out while driving if the connector is corroded and not making good contact. Had this happen on a friend's XJ... almost the exact same symptoms, it would die sort of semi-randomly and then would sometimes start and sometimes not restart. Cleaning the CPS connector fixed it and the problem has not returned.

It's so simple and easy to do that it's worth a shot at least. The same goes for cleaning the connectors for the IACV and TPS.

Dirty Wop · Jun 7, 2006

NotMatt said:
Yes, if the CPS is just plain bad, it will do the "no start at all" thing... but it can also just simply cut in and out while driving if the connector is corroded and not making good contact. Had this happen on a friend's XJ... almost the exact same symptoms, it would die sort of semi-randomly and then would sometimes start and sometimes not restart. Cleaning the CPS connector fixed it and the problem has not returned.

It's so simple and easy to do that it's worth a shot at least. The same goes for cleaning the connectors for the IACV and TPS.

Yeah, and generally speaking cleaning never hurts.

Sometimes it starts right back up, sometimes it has to work a bit more at it.

Bunk1 · Jun 7, 2006

Dirty Wop said:
-I know that the PCV valves are bad and I have some oil in the air filter (fixing all that tonight )

Any help would be greatly appreciated.

I thought it had a fixed orifice for the crank vent, I am most likely wrong. At any rate mopar has a repair kit to fix the oily air filter.

NotMatt · Jun 7, 2006

Bunk said:
I thought it had a fixed orifice for the crank vent, I am most likely wrong. At any rate mopar has a repair kit to fix the oily air filter.

Yeah, there's a good write-up on how to fix the oily air filter problem on NAXJA (or at least make it less of a problem if you have an older/worn out motor).

The gist is that the little orifice in the back of the valve cover gets plugged so all the oil laden vapors get pushed out the front and into the air box instead of getting sucked out the back and into the intake manifold.

Which reminds me, I need to go check my rig to see if drilling the rear hole out a bit bigger fixed the problem.

junkyard jim · Jun 8, 2006

Check the CPS and wiring on the trans (had the backup light wiring melt to the exhaust and only short when I hit the brakes. Took me a couple hours to figure out why it kept stalling when I hit the brakes while rolling forwards only!)

Dirty Wop · Jun 8, 2006

**UPDATE**

So I didn't get a chance to replace the PCV valves and clean out the air filter. But I removed the IACV and found that it was VERY dirty and had alot of oil in it. I cleaned it all up. Checked the elec connections on the CPS and IACV (they were good). Cleaned out the throttle body.

After starting it up it seemed to even idle a bit better. I drove it home and it was fine.

But then this morning, it has some issues starting. Numorous times when driving to work it tried to die on me when coasting to a stop, but after giving it a little gas it would stay running.

Kelly · Jun 8, 2006

Dirty Wop said:
**UPDATE**

So I didn't get a chance to replace the PCV valves and clean out the air filter. But I removed the IACV and found that it was VERY dirty and had alot of oil in it. I cleaned it all up. Checked the elec connections on the CPS and IACV (they were good). Cleaned out the throttle body.

After starting it up it seemed to even idle a bit better. I drove it home and it was fine.

But then this morning, it has some issues starting. Numorous times when driving to work it tried to die on me when coasting to a stop, but after giving it a little gas it would stay running.

CPS homie...

Dirty Wop · Jun 8, 2006

Insert ignorance here--> Is the CPS the same as TPS?

Kelly · Jun 8, 2006

Dirty Wop said:
Insert ignorance here--> Is the CPS the same as TPS?

Ones crank position sensor, ones throttle

KarlVP · Jun 8, 2006

CPS is on your bellhousing. It detects that position of the crankshaft and tells the computer where it's at. No info from it, and the engine will turn over, but won't get any spark at all.