Mechanics

99 IS INTERMITTENTLY STALLING WHEN IT IS HOT OUTSIDE.

1999 Jeep Grand Cherokee • 169,000 miles

I have a 99 Jeep Grand Cherokee 4.7L V8. It started intermittently stalling 9 months ago. At first it didn't occur very often and it would start up after a couple of minutes. It has gotten progressively worse (and the weather has gotten hotter). Now when it stalls it takes 3-4 hours before it fires right up. When it stalls, it doesn't sputter or anything, just shuts down. It will crank but won't fire. The engine temperature is always at 210 when it stalls and no codes show up. When it is running it runs great. This problem has gotten so bad that it stalls every time it is driven - making it useless. We have changed the crankshaft position sensor (and it ran great for a couple of weeks after that)we found that the wires doing to that sensor were bare, so we fixed those. We have changed the ASD relay and the fuel pump and filter. Something new that we just noticed is after it stalls, we put it into neutral and it started right up. When put into gear it shut down again. I love driving this car, but it has become to unreliable my husband is ready to push it off a cliff.

Any help would be greatly appreciated!
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Sharilord
August 21, 2012.



Does it stall while driving at highway speed or just when going real slow like pulling up to a stop sign? To restart it, have you tried holding the gas pedal down about 1/4". Also, when it starts, do you notice if it has a nice "idle flare-up" to 1500 rpm for a few seconds?

Caradiodoc
Aug 21, 2012.
It has stalled going 50mphto and it has stalled coming to a stop light and everywhere in between. When you start it it does idle up to 1500 rpms for a few seconds. One time when we started it in neutral after it stalled the security light came on. It shut down and the security light hasn't come on again (but then again we haven't driven it much).

Thank you!

Tiny
Sharilord
Aug 22, 2012.
Dandy. That rules out a low idle speed problem. Given that you have already replaced the crankshaft position sensor, which would be a logical suspect, we can rule that out. Be aware there is also a camshaft position sensor that can cause the same symptoms and those types of sensors usually fail intermittently by becoming heat-sensitive, and they work again when they cool down. Also look at the connector terminals in the crankshaft position sensor's connector to be sure the terminals aren't "spread" and making intermittent contact. We always tighten them up a little when replacing parts. You mentioned that the stalling problem didn't occur for a few weeks after replacing that sensor. That is exactly how spread and corroded terminals act. The scratching action of plugging in the connector scratches through the light film of corrosion and makes a better contact, ... For a little while.

Since you aren't getting a fault code, you might suspect a problem with the ignition switch; specifically an arced contact internally or an overheated terminal in the connector. Check its plug to see if any terminal is blackened or if the connector body is melted.

There are two other tests that can be done with the Chrysler DRB3 scanner. While driving, it will let you monitor the state of the ignition switch and the automatic shutdown (ASD) relay. If one goes to "off" when the problem occurs, we can figure out which circuit to start looking in. The second test involves driving with the cruise control engaged. When the engine stalls, do not touch the ignition switch or gear shift, just coast to a stop. Under the "Cruise Control Tests" menu it will list the "reason for last cutout". You have to view that right away before your speed drops below about 35 mph. The reason listed will be "speed" meaning as you coasted to a stop, the vehicle speed dropped below the minimum set speed, but before that, if the reason is "ignition switch", that tells you that circuit turned off while you were driving. 99 percent chance that is due to the switch itself or the connector, but the problem could be in any of the associated wiring.

If you don't have a scanner, about the only thing you can do is monitor the ASD relay circuit to see if it is turning off. That will be easier now that it is staying in the defective state for a long time. That gives you time to do some testing. Look for the wires that are the same color at all of the ignition coils and all of the injectors. That is the wire to check for voltage. You can also measure for that voltage on the smaller wires on the back of the alternator. You can use a digital voltmeter but a test light is better because the initial voltage pulse happens so quickly, a lot of voltmeters don't respond fast enough to see it. You should see 12 volts there for one second after turning on the ignition switch. At the same time you might hear the fuel pump hum for that one second. What is important is that voltage must come back during cranking. If it does, you have a fuel pump, injector wiring, coil wiring, or Engine Computer problem. All of those are relatively uncommon. If that 12 volts does not come back during cranking, there's a problem with the camshaft position sensor or the crankshaft position sensor or their wiring.

Caradiodoc
Aug 22, 2012.