Rough starts and P0740 and P0700

[cccarlson]

First of all, thanks for the add and reply’s

2006 LJ, Had a couple rough starts, thought it was just from it getting real cold here in NC. Drive this jeep every day to work, sitting at 190k. Yesterday the jeep starting and had a flashing check engine light while driving. Got back home and ended up replacing the spark plugs, testing compression and all are sitting at 180+. No codes related to this issue, but do have P0740 and P0700. Could this be the PCM? Runs better now but is hitting a severe misfire at 4k rpm no load. Going to test the fuel pressure and solenoid's this morning.

 

[Chris]

First of all, thanks for the add and reply’s

2006 LJ, Had a couple rough starts, thought it was just from it getting real cold here in NC. Drive this jeep every day to work, sitting at 190k. Yesterday the jeep starting and had a flashing check engine light while driving. Got back home and ended up replacing the spark plugs, testing compression and all are sitting at 180+. No codes related to this issue, but do have P0740 and P0700. Could this be the PCM? Runs better now but is hitting a severe misfire at 4k rpm no load. Going to test the fuel pressure and solenoid's this morning.

The codes P0740 and P0700 typically indicate a problem with the transmission, particularly relating to the torque converter and an overall transmission issue flagged by the PCM. The misfire at 4k RPM could be related to a few things. It could be something in the ignition or fuel delivery system, especially if it’s still present under load.

Testing the fuel pressure and solenoids is a smart next step. Make sure your fuel pump is providing the right amount of pressure and check for any potential blockages in the lines or injectors. In addition, consider checking the wiring and connections to the transmission and PCM to rule out any electrical issues or bad grounds. This is more common than you think and will require some thorough investigation in most cases.

If the problem persists, it might be worth looking into the condition of the ignition coils or even the wiring harness associated with them. Also, keep an eye out for vacuum leaks, as they can sometimes lead to rough running and misfires. Good luck, and keep us posted on what you find!

 

[cccarlson]

The codes P0740 and P0700 typically indicate a problem with the transmission, particularly relating to the torque converter and an overall transmission issue flagged by the PCM. The misfire at 4k RPM could be related to a few things. It could be something in the ignition or fuel delivery system, especially if it’s still present under load.

Testing the fuel pressure and solenoids is a smart next step. Make sure your fuel pump is providing the right amount of pressure and check for any potential blockages in the lines or injectors. In addition, consider checking the wiring and connections to the transmission and PCM to rule out any electrical issues or bad grounds. This is more common than you think and will require some thorough investigation in most cases.

If the problem persists, it might be worth looking into the condition of the ignition coils or even the wiring harness associated with them. Also, keep an eye out for vacuum leaks, as they can sometimes lead to rough running and misfires. Good luck, and keep us posted on what you find!

Got it all fixed after a few headaches. Ended up being a couple holes in spark plug boots. Tested fuel pressure, coil pack. Cleaned MAF, reset PCM. Went for a drive and all codes disappeared. The 4k misfire ended up just being the in park rev limiter and now I feel stupid.