Appealing to the Jeep collective mind here as I am new to the Jeep world... this is the same issue I posted on last week, resetting the computer made no difference. I drive about 15-20 minutes and the check engine light comes on. The key check method gives me 12 - 51 -55. The code lists posted here give this as O2 sensor stuck at lean condition (may be caused by bad MAP sensor system). Google searches turn up vacuum leaks and fuel pressure issues as other likely culprits.

I recently installed an APN header to fix a cracked manifold. The Jeep ran fine prior to the change except for an occasional stumble at idle. The check engine light never came on. I replaced the valve cover gasket and CCV elbows while I was at it. The vacuum boot for the metered elbow (rear of the valve cover) broke in half while I was removing it. My local Jeep parts department is impossible to get on the phone so I went ahead and "fixed" the cracked boot with liquid black tape. I also installed new quick disconnect clips, O-rings and plastic spacers on the fuel lines to the manifold while doing this job.

The Jeep runs great now, smooth idle at 900 rpm or so, plenty of power, no issues except for this "check engine" light. It always goes off when the Jeep is turned off and does not return until another 15 minutes or so of driving. I started checking things this morning. The "fixed" area of the boot appeared to have some pinholes through the liquid black tape repair, would a small vacuum leak in the CCV system cause a lean fuel condition and this code? As far as the fuel lines go, I do not see any fuel leaks around the manifold connections and don't know what else to look for as far as fuel issues that could cause this.

Finally, I pulled the MAP sensor this morning intending to test it per the write up posted here: http://www.cherokeetalk.com/forum/f6...rocedure-1261/ . I was rather surprised to find a MAP sensor with a "GM" label... Also, I was not sure which wires were terminal A, B and C on the harness as mine is not labelled in any way. Anyway, I am feeling a little mentally thicker than usual this morning, but the write up did not seem to indicate where the negative probe from the meter goes while testing the sensor. Does this get grounded on the firewall, touched to terminal A or connected to some other location? Any input or ideas would be greatly appreciated as I really do not have much more in the budget to throw at this right now and I do not want to replace random parts trying to troubleshoot if possible. Pardon the lousy cell phone pics, but here is one of the sensor with harness and one of the repaired vacuum boot.

 

For future reference, replaced the MAP sensor, problem solved.

 

Thanks for the follow up. Haha. Sorry you didnt get more help but you may have helped me. I also just put an apn header on and am getting codes 14 and 51.

 

My 94 Jeep XJ was running like crap, losing power, shutting off while driving, and threw a code 51. Replaced MAP sensor and CCV elbow and emission tubing. Ran like a new Jeep with POWER for 3 days and now doing same crap. Any ideas would be greatfully appreciated.

 

Check www.teamcherokee.com for a full set of those weird sized vacuum hoses and tubes. Prices aren't bad either.