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kennyb28, Service Manager
Category: Jeep
Satisfied Customers: 355
Experience:  Service Manager with many years of hands on experience
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Jeep Grand Cherokee: 1999 Jeep grand cherokee with misfire

Customer Question

1999 Jeep grand cherokee with misfire on cylinder 5 code. Replaced spark plugs, fule injector, muffler, engine flush, oil change, air filter, fuel filter and belt. Did compression test and seems to be fine. Do not know what else it can be. Other symptoms are hard idle when in drive, or going in reverse as well as around 40 to 50 mph. Spark plug has smell of gas to it.
Submitted: 4 years ago.
Category: Jeep
Expert:  kennyb28 replied 4 years ago.

Welcome to JustAnswer! I'm Kenny and ready to get started helping you.


What were the compression readings?


Have you tried to clean out the carbon in the cylinder?


Have you checked to see if the plug is firing on this cylinder?

Customer: replied 4 years ago.
I am not sure of the compression readings because it was Tuffy who did it. The spark plugs were just replaced last week and I believe it is firing but for some reason we keep getting an error code of P0305 and P0702. It is so strange. Tuffy told us to replace our gas cap? I am not sure if they tried to clean out the carbon. How would we do this?
Expert:  kennyb28 replied 4 years ago.
I realize the spark plugs were replaced but may have an issue with the coil or the powertrain control module not firing the plug. I would start by cleaning out the carbon as you may have a valve sticking or not seating correctly and either one can cause a misfire. The make products you spray into the vacuum lines that will go into the engine and clean out the carbon. You can get this at any parts store. Just ask them what they carry and what they recommend and just follow the directions of the can
Customer: replied 4 years ago.

Do we need to change the coil pack as well? My jeep has 110,000 miles on the engine and it is the original?

Expert:  kennyb28 replied 4 years ago.
It is possible it is causing the problem and also possible the powertrain control module is causing the problem. The coil is easier and cheaper to replace than the powertrain control module and would try it before the powertrain control module