Jeep TJ misfiring when warm

Jakob McElhaney

Jakob McElhaney

New Member
Joined
Oct 3, 2017
Messages
13
Location
Zanesville, OH, United States
Looking for help again with my 97 Jeep TJ 4.0. Within the last 300 miles, I’ve replaced the exhaust manifold, plugs, wires, distributor cap, ignition coil, upstream o2 sensor, and also went and done the heat shield on the exhaust manifold, fuel rail and injectors. I’ve been chasing a battle of a horrible misfire when this thing gets hot. Especially when the temperature is hot outside. When trying to start it back up immediately, it will still miss, but it reeks of fuel. IMO, it has to be a heat soak issue. Any ideas or help? I’m tired of throwing money at the thing, and I would like to be able to enjoy the jeep with the nice weather.
 
It could be a bad upstream O2 sensor, they will screw up the air fuel mixture after the engine warms up which can cause all kinds of problems including misfires.

If you replace it make sure it is an NTK O2 sensor. Avoid Bosch and aftermarket.

Don't waste your money replacing the downstream O2 sensor too, it only monitors the catalytic converter and has nothing to do with how the engine runs.
 
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Reactions: Potomus Pete
Have you put a scanner on it to see what codes it's throwing? If it's misfiring on all cylinders, there is a likelihood of a bad upstream O2 like @Jerry Bransford said.
However, if you're experiencing a specific cylinder misfire there could be numerous causes.
 
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