Mechanics

MY TRUCK KEEPS SHUTTING OFF ?

1996 Jeep Grand Cherokee • 6 cylinder 4WD Automatic •

Ok so I just got a jeep from a car lot and as soon as I drove off it cut off so they came and got it and put it in the shop. They kept it for 2 weeks saying it never shut off on them so when I came get it I did a test drive with one of the owners and it shut off, so I took it to auto zone and got a diagnostic test. I changed my muffler cause it had a huge hole in it, I got new spark plugs and wires and they all got changed, and a new ignition coil but my truck seems to keep back firing and shutting off. My car lot said my starter, my alternator, and my battery are all good so what keeps making it shut off?
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5wagged5olo
March 22, 2014.




The backfiring has me concerned, but if it's only doing that as a result of the stalling, and not while you're driving, what has probably happened is the idle speed is too low. It is real common for car batteries to go dead while the vehicle sits on a used car lot. That can happen in as little as three weeks. When that happens, or when you disconnect the battery, the Engine Computer loses its memory. It has to relearn "minimum throttle" before it will know when to be in control of idle speed. Until that occurs, hard starting and stalling can be expected unless you hold the accelerator pedal down 1/4". On Chrysler products meeting the conditions for the relearn to take place is pretty easy. Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

Caradiodoc
Mar 22, 2014.
WAS IT BACKFIRING THE 1ST TIME? (I KNOW IT WAS SUCH A SHORT PERIOD OF TIME)

MAYBE IF THIS IS A NEW SYMPTOM, THEY POSSIBLY MONKEYED WITH THE TIMING WHILE IT WAS IN THEIR SHOP?

OK.I STAY OUT NOW AND WATCH YA'LL HASH IT OUT

THE MEDIC
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Tiny
CJ MEDEVAC
Mar 22, 2014.
It backfires when I start it or right before it cuts off

Tiny
5wagged5olo
Mar 22, 2014.
If low idle speed isn't related to the problem, you're going to need a scanner to view live data. Most have the ability to record a few seconds of sensor data when the problem occurs. Later, it can be played back slowly and you can see what changed. In particular, I'd be watching the crankshaft and camshaft position sensors' signals to see if one is dropping out. They're responsible for ignition timing, and backfiring is going to be related to incorrect timing.

Caradiodoc
Mar 23, 2014.

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