Soooo, I had the dreaded P300 code pop up randomly for the last 2 years. Sometimes it would be P301 or P306 and everything in between. It would happen at idle or above 3k rpms. There seemed to be no rhyme or reason as to when it would go off. It should be noted that this is in a 2000 Jeep TJ with a 4.6 stroker and 32rh auto trans with all new parts and only 8k miles on the motor. I know its not the stock 4.0 but the testing procedures are going to be the same. I started going down the rabbit hole of testing parts or just flat out replacing them. I even went as far as to pull the engine bay wiring harness and ohm each wire if it was bad or even looked bad I spliced in new wires. Here's a list of everything that was replaced through the last 2 years just to show what has been done.
Spark Plugs 3 different sets // Coil // CPS at least 4 all OEM // Fuel pump // fuel rail // 3 sets of injectors // Cam position sensor and synchronizer // all new sensors on the throttle body // Flywheel // Cats.
Basically I replaced or tested anything that had something to due with spark or fuel.
Here's what finally fixed my random P300, I used the Autel Maxicheck MX808S to test everything and of course it all passed, looking through its functions I noticed a test called "synchronization" I thought what the hell lets give it a shot.
What this test does is bump the rpms up to 1k and measures the cam sensor signal and crank position sensor signal and sees if they are in sync. Mine was not, it was off by 15 degrees.
I had the cam synchronizer facing the firewall like all the forums say and the manuals but the signal was off. This test is done in real time so with the motor running I loosened the cam synchronizer bolt just enough to move the synchronizer until the signal showed 0 degrees, the MX808s then gave me the "in spec".
Its been close to 500 miles from highway miles to trails and no P300 codes at all. Not sure if this will help with your P300 but this is what worked for me.
Spark Plugs 3 different sets // Coil // CPS at least 4 all OEM // Fuel pump // fuel rail // 3 sets of injectors // Cam position sensor and synchronizer // all new sensors on the throttle body // Flywheel // Cats.
Basically I replaced or tested anything that had something to due with spark or fuel.
Here's what finally fixed my random P300, I used the Autel Maxicheck MX808S to test everything and of course it all passed, looking through its functions I noticed a test called "synchronization" I thought what the hell lets give it a shot.
What this test does is bump the rpms up to 1k and measures the cam sensor signal and crank position sensor signal and sees if they are in sync. Mine was not, it was off by 15 degrees.
I had the cam synchronizer facing the firewall like all the forums say and the manuals but the signal was off. This test is done in real time so with the motor running I loosened the cam synchronizer bolt just enough to move the synchronizer until the signal showed 0 degrees, the MX808s then gave me the "in spec".
Its been close to 500 miles from highway miles to trails and no P300 codes at all. Not sure if this will help with your P300 but this is what worked for me.
