1998 Jeep Grand Cherokee Engine Randomly Shuts Off.

First, we have to know which engine you have when discussing an engine running problem. Next, you said it won't turn over. That's a starter system problem, but you're also describing a stalling problem which would be related to loss of spark, fuel, or both.

Have you checked for diagnostic fault codes? Do you know how to do that by cycling the ignition switch?

You're confusing "turning over" with starting and running. Turning over and cranking are the same thing. Once it's turning over, if it doesn't start, that's a no-start / stalling condition. I understand now that you have a no-start condition that started out as an intermittent stalling problem. Most commonly that is caused by a failing camshaft position sensor inside the distributor or a crankshaft position sensor. Either one can become heat-sensitive, fail when the engine heat migrates up to them, then work again after they cool down for an hour.

Most of the time a failure of one of those sensors will set a diagnostic fault code, especially if they stop working while the engine is running, but those codes won't turn on the Check Engine light. Only codes related to things that could adversely affect emissions must turn the light on. Chrysler makes it real easy to read engine fault codes yourself. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the code numbers show up in the odometer display. Hopefully there will be one to give us some direction. If not, the next step is to determine if there's spark and fuel pressure, and if the automatic shutdown relay is turning on.

I have to run out of town for a while. I'll check back later tonight to see how you're doing.

Let me add a couple of observations. First of all, a paper spacer is needed to set the critical air gap of the crank sensor. If the gap is just a fuzz too big, you can get the exact symptoms you're describing; an intermittent no-start, intermittent stalling, and even a backfire. Second, if the battery was disconnected or run dead recently, the Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. The engine will be hard to start unless you hold the gas pedal down 1/4". It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine, and the engine will want to stall when coming to stop. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

For checking fault codes, try cycling the ignition switch four times, just to be sure, but three is all that should be needed. If the starter ever tries to engage, even for an instant, that aborts the test. You'll have to wait a few seconds, then start over.

Chrysler fuel pumps almost never quit while they're running. That's common for GM pumps that let you sitting on the side of the road. When the brushes are worn in the motor, Chrysler pumps fail to start up. You won't hear the hum for one second after turning on the ignition switch, and you won't have any fuel pressure. The clue to looking at the pump is you'll still have spark.

My guess is that noise has something to do with a shorted starter motor or corroded battery cable, but to be sure, look for the starter relay in the under-hood fuse box. Bypass that to see if the same noise occurs. You can remove the relay, then use a piece of wire or a stretched-out paper clip to jump terminals 30 and 87 together, or you can remove the cover from the relay, reinstall it that way, then squeeze the movable contact.

Think of the fat battery cable going to the starter as a garden hose. If you step on the hose and partially kink it, the water will just dribble out the end. That water won't have enough power to do anything. Also, if you unscrew the nozzle, the water will run wide open but won't be able to build any pressure either, so it won't have the power to do anything. A corroded cable is like standing on the hose. You can't get enough current through it to run the starter motor. When you try to run water current through the restriction in the hose, you lose all the pressure. When you try to energize the starter, it draws so much current that the voltage drops. Voltage is electrical pressure. When the voltage drops enough, other things that are turned on are also affected. In this case you see the results of low voltage when the interior lights get dim, but the starter solenoid is also affected. There's actually three switches involved with the starter. The last one is that solenoid which also does mechanical work. Because of the low voltage, the spring-loaded solenoid doesn't have enough power to stay engaged, so it releases. When it does, it turns off the very high-current switch to the starter. If you turn off the faucet feeding the hose, standing on the hose has no effect on anything. When the solenoid turns off, that high current to the starter stops trying to flow. As a result, voltage goes back up. That higher voltage is what the solenoid needs to engage, so that's what it does, then the process repeats again. That solenoid typically turns on and off multiple times per second, and the lights will flicker in time.

You can expect the same results when you bypass the starter relay. We're just doing that test to verify it's a starter circuit problem and that we don't overlook something unusual. The ignition switch can not handle much current without overheating. It passes a fraction of an amp to run the starter relay. The contacts in that relay can only handle about 15 - 20 amps, but that's enough to run the solenoid built into the starter motor. When the solenoid engages, it first runs a small gear into mesh with a ring gear, then it turns on a high-current contact to pass about 150 - 200 amps to the starter motor. You have to have really beefy cables and solid and clean connections to pass that much current.

Excessive resistance anywhere in that circuit can cause a buzzing noise from the train of events I described, but besides bad connections, corroded cables, and the rare shorted starter, a bad battery will do the sane thing. You can find that by measuring its voltage while under load. It's hard to do that when running the starter because that voltage will be pulsing, but you may be able to determine the battery's condition by turning on the head lights and heater fan. A good battery that's fully-charged will read 12.6 volts. Without going into a lot of unrelated details, if the battery has a shorted cell, you'll find it's around 11 volts.

The sound in your video does not sound like the normal buzzing caused by any of the things I listed. That's why you should bypass the starter relay and verify the same noise occurs. By leaving the ignition switch off, nothing else will be trying to run.