Stumbling overheating and code p171 and 172 -
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Unread 06-08-2013, 10:42 PM   #1
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1996 ZJ 
Join Date: Jan 2013
Location: JBER, alaska
Posts: 32
Stumbling overheating and code p171 and 172

Ok so I have a 96 4.0 and I am driving from alaska to oklahoma haling a trailer. After a while out on the highway I have had a issue where it feels like it is having issues getting enough fuel. I have 703 injectors I just replaced the fuel pump at a hotel parkinglot by the way and has a new fuel filter. Can't ququiet figure out what the issue is any help would be helpful

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Unread 06-08-2013, 11:40 PM   #2
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Those codes are for a bad upstream oxygen sensor, which would cause the stumbling. Mine did the same thing when it went bad, even caused stalling at the end of it's life. It sends the fuel/air mixture readings to the PCM.

The overheating could be a number of things. Need more specifics of when/how it overheats.
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Unread 06-09-2013, 03:58 AM   #3
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1996 ZJ 
Join Date: Jan 2012
Location: Central, Ohio
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^ agree, on those codes are for a bad upstream o2 sensor. Only go with NTK/NGK which is OE and your upstream is a NTK 23121 available from Rockauto for $32.79 or Amazon for $40.

Curious what brand fuel pump you installed and did you replace the whole assembly or just the pump? If a new o2 sensor doesn't solve your problems you can get a loaner fuel pressure tester for attaching to the fuel rail at most auto parts stores. Your spec is 49psi +/- 5lbs. Have even heard of some duct taping the gauge to the outside of the windshield so you can check the pressure while driving down the highway.

Not sure about the overheating but have you flushed the cooling system lately and is the 190* thermostat still good? Is your header cracked at the welds where the tubes come together which is a common problem on your 4.0? I had to replace mine on my 96 4.0.

I'm also running new 703's, which took quite a while to adjust, along with a new Bosch fuel pump assembly which works great. Good luck.
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Unread 06-09-2013, 09:15 AM   #4
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1998 ZJ 
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Anecdoctally, some were saying the 703's lean out at higher rpm's but that is just internet stuff. But hypothetically, and this is a question more than a statement, if they did in highway driving with a maxed out duty cycle would the jeep throw a 02 code and possibly overheat from the lean condition? I don't understand all that stuff so just asked.
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Unread 06-09-2013, 11:47 AM   #5
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Ya in theory, and I say overheating it was running at the upper side of where I felt conferrable with it. I changed the o2 sensor the old one I think was original and the truck has hi mileage. I had already replaced the rear one. We will see if it helps tonight. I am leaving Colorado Springs for Stillwater OK the last 600 miles of my trip. To answer the earlier question I just replaced the pump and pre filter that's all I could find at the time. I wonder if some of it is the elevation change it truck has lived most of its life at sea level and when I have had the most issues out of it is at higher elevations. Just a thought.
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