Misfire/Spluttering Issue

[NBM]

Hi all,

I'm in desperate need of some help with my KJ. Recently there has been a very intermittent misfire/spluttering when driving. This usually happens at higher speeds, but can happen at other times as well. What happens is it will (out of nowhere) chug a bit, and then shudder as it struggles to keep speed (occasionally it will just lose speed). During this time the CEL/MIL will come on and also the ESP light (no idea if this is even related) - sometimes the MIL will flash. The flashing is always remedied by restarting the car and the issue goes away until the next time. This problem only happens sporadically, so sometimes I can go 20-30km's without it even happening.

Have had a look at the codes and it's showing PO300 and PO339. At this stage, the spark plugs, ASD relay and fuel pump relay have all been replaced. The cat doesn't glow red after driving, there is no smoke blown etc. I know PO339 is the crankshaft position sensor, so that has been ordered and will be changed this week.

Can anyone help me please!

Thanks in advance.

[projoe]

The advise given in this forum to check a faulty cps is to pour cold water over it while the engine is missing & carrying on if the engine starts to run smooth you've found your problem. have you ordered a Mopar genuine cps it seems to be the concenssus on this forum that they are more reliable.

[NBM]

Thanks for the reply projoe.

Unfortunately I can't really do that test as it happens so sporadically that I can't get it to misfire on the driveway etc. and even if I carried water with me, by the time I pull over it's generally stopped.

I did order a genuine CPS though, so hopefully it should fix the issue - although I'm planning on the worst.

[Hayesio]

I think you are on the right track. P0300 is Multiple Cylinder Misfire and as you say, P0339 is Crankshaft Position Sensor Intermittant. I would think the dodge crank sensor would cause the misfire. Also, the ABS control module need to know engine speed, at all times. With the crank sensor playing up, its not happy so thats why you are getting that light come on.

[NBM]

Just a follow up on this, and for anyone who has the same problem in the future. The CSP eventually came in from Jeep, and it was the issue!

Changed it over, and she has run perfectly since (done over a 1000km since). My big tip to anyone else out there is make sure you get a genuine CSP, not one off amazon etc. They are only about $50 from Jeep.

Thanks for all your help guys!