1997 GC Laredo 4.0L I6 with about 97K on it. All started with a check eninge light and a LOT of exhaust noise. Pulled the code and got a 51- O2 sensor sez lean so the fuel system is dumping gas into the engine, which has caused the cat converter to overheat and go to pieces. While I'm down there, I discover that the exhaust manifold is cracked (suprise) and I figure the leak has caused a faulty O2 sensor reading. I replaced the exhaust with a Thorley tri- Y header, a Magnaflow high flow converter, and a flowmaster series 70. (If you have a typical Jeep exhaust manifold crack I HIGHLY recommend this upgrade- email me if you want to hear more about it) Also replaced the downstream O2 sensor- with a Mopar- since I was replacing the cat. Didn't replace the upstream one because I used the stock head pipe. Also replaced the blackened spark plugs. Ran a can of additive thru the gas to clear out the carbon. After all that I still have my code 51. I took the Jeep to the dealership who helpfully charged me $165 to tell me that there was nothing wrong- my upstream 02 sensor was "lazy."
So I replaced the upstream O2 sensor today and so far the light is out BUT while I was under there I discovered that there is a vacuum line running from the front diff that is just hanging loose. I wouldn't swear I didn't knock it loose during the exhaust replacement, but I've looked everywhere and can't find a vacuum port for this hose to fit on. My 2 questions are this: 1) Does anybody out there know where the vacuum line from the front diff is supposed to connect and 2) What is the likelihood that the vacuum leak is causing my lean condition.
Thanks for any help! Stu snipped-for-privacy@yahoo.com