Jeep Cherokee Cutting Out Periodically

[Swimmer]

I've had the old '93 Cherokee in to my trusted shop, they replaced the coil, checked the fuel pressure -- its OK. A couple days later she died again (instantly turns off while running down the road-- accessories still working -- will sometimes restart in two seconds on its own or I can restart it in Nuetral while coasting, then eventually it will not restart unless it sits for hours), brought it back to the shop and it wouldn't act up for them. So, I took it back and the same thing happened 30 miles later. Any ideas would be appreciated? Neutral safety switch (my thought, but shop said no)? O2 sensor?

[Jeremy airjer W]

Pickup-coil! Its located under the distibutor cap. Try tapping lightly with a hammer sometimes this will trigger the pick-up coil to act up.

Did they have crank sensors in 93? if they do this could be the other possibility. Typically the crank sensors will short and you see a loss of power to things like the coil, injectors, and some other computer controlled devices/sensors.

[Swimmer]

Thanks for the quick response airjer. My mechanic replaced the "ignition coil" the first time around and said he checked the crank/cam sensors and they were OK. I assume the pickup coil is the same as the "ignition coil"? I have an aftermarket remote start in that vehicle...wonder if that could be it?

[Can'tFishEnuf]

I had the exact same thing happen to me with my 98 Cherokee. I changed out all the ignition hardware and it got better but would still do it every once in a while. I took it to a dealer and they couldn't find anything wrong with it. Of course it didn't act-up while they had it. I was at an AutoZone looking for some part to try and the guy there asked me how old my battery was. Anyway he said that he had heard about Cherokees cutting out when the battery gets old and weak. I went ahead and put a new battery in and it hasn't done it since. That was about 3-4 years ago. Sound a little wierd, but it worked.

[Jeremy airjer W]

No they are not the same. The ignition coil is the part that produces spark. The pick-up coil is the sensor that tells the computer when to fire the coil.

[BlueBasser]

I had the same problem on my 91 Cherokee, for me the problem was that the fuel pump had rusted, I also had problems with the Neutral switch. I would just hit my automatic shifter and it would usually click in. I know how much of a pain it is because it never acts up once they get it to the shop! Good luck

[Jeremy airjer W]

The only Purpose of the nuetral safety switch is to disable the starter if the transmission is in any gear other than park or nuetral. Once the vehicle has started the switch plays no part in its drivabilty.

[Swimmer]

Thanks again guys. The fuel pump seems to check out OK...I think it would show weakness all the time if it was bad. And airjer, I messed around (moved it while Jeep was running) with the wire coming out of the distributor (that I think is connected to the pick-up coil) and I was able to get the motor to hesitate. Also, the connector for that wire was laying against the ignition coil, and I wondered ir that may effect anything. So, the next step is to open the distributor cap and inspect...I'll probly not see anything so I'll go to Carquest and spend 86 bucks on a pick-up coil or 75 on a remanufactured distributor with a new p-up coil in it. You tell me why the one is cheaper that the other?! I should be able to loosen and move the tab holding the distrubutor down, lift it out, and stick the new one in? Darn, I hope thats it. I'll call you a genius in advance airjer!

[End of the Line]

Had a 1988 chevy corsica with the exact same problem. Same thing, take it to the shop, checks ok. There was 2 coil packs, no distrubutors. They changed one coil pack, turns out it was the other one that they finally tracked down later. Not sure if the Jeep has that, but just thought I'd throw that out there.

[john.wells]

the only real good way to check the fuel pump is to put it on a lab scope to read the pulse width from the pump motor. You could have dead spots in it. Another possibility is a wire periodically grounding out. Spend a little time jiggling wires (not your spark plug wires!) around while the engine is running to see if you can get it to act up. Be careful when doing this, obviously.

[Jeremy airjer W]

Over the years I have seen a couple of bad wires cause problems. Mostly on Fords (the ever popular wiggle test is a factory prescribed diagnostic aid) and one chevy and one chrysler.

The blazer was an intermittent stall with no rhyme or reason it had a broken wire near the coil connector. The insulation was in tacked so there where no obvious signs that it was broken internally. I bumped it by accident trying to figure out what was going on.

The caravan was a no start. The previous shop had replaced the crank sensor and returned the vehicle to the customer. The customer made it to us and I had my turn with it. Every indication showed a week crank sensor. I verified it with the lab scope and the generated signal was not as strong as it should have been (this should have been my first clue). I requested that we replace the crank sensor to eliminate the possibility of a bad part, Still would not start. Backprobed the computer and had the same signal unplug the sensor and Full signal returns. Aha, I have a wiring issue. Sure enough the loom around the wiring harness had become brittle and pieces had fallen off. The harness had rubbed a spot of paint off the trans pan, about the size of a quarter, to expose the steel. The insulation on the signal wire from the crank sensor also rubbed through causing it to poorly ground to the pan. repaired the wire and harness and it ran like a top!!

[Swimmer]

Yup, I've jiggled and re-jiggled every wire on that sucker. I hope to have time to look at and fix? it today...I'll let you'all know if it works. Airjer, how long does it take for the coil charge to disipate?? I got zapped once a few years ago and I remember it wasn't a fun feeling.

[Jeremy airjer W]

A coil shouldn't zap you unless the vehicle is running or possibly when the key is on. You probably thinking of a condesor which was used with a points ingnition system. We still still like to order one of those up every once and a while and either charge it up and zap the new guys or send it back to the parts store and waite for the phone call thanking us for the laugh!!

[Swimmer]

Ya, pretty funny once you get over the "shock". It was my old Buick 455 Rocket motor that sent me to the moon.

[Swimmer]

OK, so I got the rebuilt distrubutor in over lunch. The rotor was pointing exactly perpendicular to the block, so I thought there would be not problem aligning it. Of course, the gears in the crank must have turned some when I took the old one out. So, it will not "run". Now I need to find TDC, right? Pull out #1 plug and wait for compression pressure on your thumb, then turn rotor to #1 plug and insall distrubutor. Does this sound right?

[upnorth]

I think the best would be to put something in the number 1 plug and turn until the piston reaches its highest point and also make sure the timing mark on the crank is lined up and then make sure the rotor is pointing to the number one plug wire.

[Jeremy airjer W]

Yup feel the pressure and line up the timing marks on the crank pulley.

Or after you feel the pressure on your thumb, take a long screwdriver and stick it in the spark plug hole when it stops going up you're right around TDC (you would be amazed how many vehicles timing marks are missing or are no longer visible or are rotted away in MN). You may have to play with turning the distributor a little bit to get it started but you should be right in the ball Park.

I guess we where posting at the same time. The reason you want to feel for pressure is that the crank will turn two times for every one crankshaft revolution. If you simple install the screwdriver and wait till it stops going up there is a chance you will end up 180 degrease off.

[Macgyver55]

Quote:

---

the crank will turn two times for every one

crankshaft

revolution.

---

Air, I'm thinking you meant to say camshaft not crankshaft here.

[Swimmer]

OK, just got back in after install. No go...will not fire. I pulled the distributer out, then put some white-out on the crank mark, put a socket and breaker bar on the crankshaft bolt and turned the crank until the white crank mark aligned with the zero on the timing plate. The flashlight showed the #1 piston close to max. Then turned the rotor so it matched up with #1 plug on the cap. Stuck the distributor back in, bolten it down, rewired and nada, no fire. This is the type of distributor that I don't think you can turn the body to further adjust...part of the body forms the "U" bracket that the bolt goes into to lock the whole down. Am I missing something? Does the proceedure sound valid?

Is it possible even at TDC to be 180 degrees off?

[Macgyver55]

Even if it is in wrong it should at least pop or backfire when cranked. If it is not even doing that, the distributor may be just be a defective one. Have you cranked it and checked for spark?

[Swimmer]

Havn't checked for spark yet. I got a bad feeling that it wasn't the pick-up sensor that caused the original problem...and the original problem is the reason that it will not fire now...it was a good suggestion to try this though. Any other ideas?

[Jeremy airjer W]

Ah no, The Crankshaft has the smaller pulley, half the teeth of the Cam pulley. The crank has to turn twice as many times as the cam. So for every two revolutions of the crank you get one revolution of the cam. oh, wait a minute I see what you are sayin yup that was a typo!! Crankshaft turns two times for every 1 camshaft revolution

So yes it is possible that you have the distributor in 180 off. When the crank is aligned with the TDC mark the piston may be at TDC or it may be on the exhaust stroke. However you should hear something as you crank like the above mentioned.

If your getting nothing then why not drop the old distributor back in and see if it fires. It ran before you put the new one in right? This would let us know if the distributor is defective or not. If it doesn't fire than check to see if there is 9 volts on the orange wire going to the pickup coil connector. There should be 9 volts when you turn the key on (you'll have to have somebody turn the key for you, the auto shutdown relay will only stay on for a short period of time, once it turns off you will not see any voltage. If you see voltage I still think we are on the right track. If you don't see any voltage than disconnect the crank sensor plug located on top of the intake near the firewall. This should also have a orange wire to it. Then check voltage at the pickup coil again while somebody turns the key on. If you now have 9 volts than you have a shorted out crank sensor.

Hope that helps!!

P.S. Where did you get the parts? Never mind I see you said carquest. They usually are pretty good and pretty reliable.

[upnorth]

Yeah, I forgot about that earlier, my bad. You need to be on the compression stroke. You may be trying to fire on the exhaust stroke. And with no compression it just ain't even going to try to fire.

[Swimmer]

Thanks again guys. Could it be on the exhaust stroke, even if the timing mark is lined up at zero and we could see the piston through the #1 spark plug hole in the extended postion (using a flashlight)??

Airjer, I will try using the multimeter next week. The Jeep is stuck at work and I have till Wed. off.

[upnorth]

Like some else posted earlier the crank turn two revolutions to each revolution of the camshaft. 1 revolution is the compression(valves closed) the other is the exhaust(valves open). So yes you could be sending spark during exhaust revolution and there is nothing there to ignite.

[Jeremy airjer W]

Yes it is! In a four stroke egine the piston will make four strokes, up twice, down twice. The camshaft and the distibutor are turning at half the speed of the crankshaft. Each piston goes up twice and down twice for every "cycle"

This is for the number one cylinder

Intake - piston goes down, intake valve is open, Timing mark is at TDC, distibutor rotor is pointing away from #1

Comression - piston goes up, all valves are closed, timing mark is 180 from TDC, rotor is 1/4 turn away from #1

Combustion - piston is at the top of its stroke, timing mark is at TDC, Rotor is pointing at #1

Exhaust - piston returns up, exhaust valve is open timing mark is 180 from TDC, Rotor is 1/4 turn past #1

So if you put the distributor in with the rotor pointing at number one while the piston is at the end of exhaust/beginning of intake (or up all the way) and the timing marks are at TDC then it will be in 180 off.