Question about 1991 Jeep Wrangler

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Why does my jeep backfire and shut off when i drive

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  • Greg McCarthy Oct 04, 2010

    How often does it backfire and shut down?Backfire is too much air,not enough gas...most likely a lack of gas.Backfire is very serious and you need to avoid driving this vehicle until it is fixed if possible.Backfire causes alot of heat real fast,although it may not show on temperature guage,and i have seen it blow a hole right through a piston which is very expensive repair.It is basically an explosion in your combustion chamber and when the valves are closed,there is very little room for the explosion gas to escape.With the newer 4 valve per cylinder systems,it is slightly better,but only slightly because it is a very fast occurring explosion.As you can see,I cannot stress that enough.Once I was driving on the highway on a bike with some friends and we were about 30 miles away from our start point.All of a sudden one guy's engine boomed and shut down,would not start.We had to wait an hour for the rest of the crew to go get the rescue truck,come back and load it.When we took it apart the next day,there was about a 1 and a half inch diameter hole in the piston.Your best bet to see is if the fuel pump relay is working.Usually,when you turn on the key,the gas guage should start going up to your current fuel level.I have a 1995 diagram for a Wrangler and that is directly an output from the PCM.I would imagine 1991 should be very similar.The next to check if that is good will be tougher.You need to check the fuel pump,maybe injection system,which both are affected by the PCM.Easiest would be to make sure gas is coming out of injectors.If you get past that and all is good,just reply here and I will get an autolink to your post and will reply ASAP and we'll try to figure this out.Good luck!Greg


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Worn spark plugs and /or spark plug wires are the most common cause. Not sure what maintenance was performed, but with the info provided, this would be the first place I would suspect.

Posted on Oct 04, 2010

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