Hey guys, I have a 2002 Jeep Wrangler Sport 4.0. I have been chasing down a misfire for almost two years now. I have replaced spark plugs and coil rail with no luck of fixing it. I have codes for multiple cylinder misfire and misfire cylinder 6. I took it to the dealership recently to see if they could pinpoint what’s going on. They said the next step would be to do a compression test. They didn’t tell me whether or not it could be the injectors. Then they called me a couple days later and said they can’t do a compression test because it isn’t ACTIVELY misfiring, it only has the codes for a misfire. They said if they do a compression test without it actually misfiring then the results would come back normal. I’m confused. Isn’t that a good thing? Doesn’t that mean the engine should be fine and that the misfire is coming from something else? What do you guys recommend me do? Should I do a compression test myself? Should I replace injectors? Or do you guys think since it’s not actively misfiring or jumping could it just be a sensor throwing off the system? The jeep isn’t noticebly running badly, but I definitely want to solve this problem. Thanks.
Multiple Cylinder Misfire/Compression Test
- Thread starter JBarger94
- Start date
ohiopatriot
TJ Enthusiast
Compression won't come and go. Either the engine is sound or it's not. It won't hurt to do a test just to confirm engine condition, but you have some other problem.
Without proper equipment, I would move things around. Move injector from six to one. Move spark plug. Just to see if miss follows.
Without proper equipment, I would move things around. Move injector from six to one. Move spark plug. Just to see if miss follows.
Examine the wiring around the fuel injectors, 02 sensor, and crankshaft position sensor.
A short in these wires could set off a misfire code.
Make sure there are no bare wires that could arc under a load.
Check the plastic loom wire covers, if they touch an exhaust manifold, it melts a hole in the loom and can cause a short.
I fixed my code 43 misfire this morning by replacing the loom and re routing the wiring to keep it away from the exhaust mani
A short in these wires could set off a misfire code.
Make sure there are no bare wires that could arc under a load.
Check the plastic loom wire covers, if they touch an exhaust manifold, it melts a hole in the loom and can cause a short.
I fixed my code 43 misfire this morning by replacing the loom and re routing the wiring to keep it away from the exhaust mani
How well does it start? I ask because I had a misfire code for cylinder 1 that would come on. I swapped injectors and spark plugs, trying to see if the code would follow. It did not. I also had a bad check valve in the fuel pump. When I fixed the fuel pump, the misfire went away.
..wow, a misfire caused by a bad check valve in the fuel pump?
That is the last thing I would think would cause a misfire.
May I ask how in the world you were able to trace the problem to the bad check
valve ?
I would have never made the connection
It was an accident. I was fixing a hard starting problem. Only thing I could figure is that I wasn't getting enough pressure while it was cold...whereas the new check valve keeps the system pressurized so it doesn't have to work OT to build back up. Engines need more fuel when cold, and I only got the misfire code when it was idling and cold...wow, a misfire caused by a bad check valve in the fuel pump?
That is the last thing I would think would cause a misfire.
May I ask how in the world you were able to trace the problem to the bad check
valve ?
I would have never made the connection
Ok guys, so I have attempted multiple compression tests and none of them are working. I have used two different test kits and every time I am cranking the engine the needle on the gauge just bounces up and down and won’t give me a reading. Am I doing something wrong in this test? I’ve removed spark plugs, coil rail, and fuel pump relay just like everyone I’ve asked has said to do. The gauge is threaded into the spark plug hole, but it will not give me a reading. Is there a specific compression test kit I should be using for the Jeep TJ? Or are they just bad gauges?
ohiopatriot
TJ Enthusiast
There is a Schrader valve that appears to be working but for some reason compression gauge still won’t hold a reading. If anyone has done a compression test themselves on a TJ please share which tester you used.
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