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Old September 9th, 2015, 19:30
ewert35 ewert35 is offline
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Location: denver co
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Engine Dying Issues - Uphill and at Elevation

Dear Members,

I desperately need your help on this one. Friday I went to run Red Cone. I left my house in Erie and drove all the way up to the trail without any issues. Approximately 25-30 minutes up the trail, my jeep just died. I could hear the pump starting up, the engine was turning over like a champ, and I bleed off the injector flatter value and had liquid gas pour out, it just would not catch. I even smelled gas from the exhaust when attempting to start. After about 15 minutes it started right up and I continued up the trail. About 10 minutes later, my Jeep died again. We spent the next 2 hours winching around on the narrow trail to get me turned around to get off the trail, and right before we were about to hook up and head down the trail, it started up again. I was then able to drive down the trail and all the way back to Erie without issue. I even stopped in Conifer, shut off the engine, and it started up again.

When I got back home, I decided to drop the tank and replace the fuel pump, since the Jeep has about 150,000 miles on it, and I figured its first replacement might be about due. When I took out the old pump I was just about 99.9% sure that was the problem. The fuel gauge float and the filter had broken off the pump assembly and were both floating in the gas.

Once the new pump was installed, I started her up, and it was running great. I noticed the engine turnover was much quicker and the engine was roaring to go. I then drove up on Sunday and attempted Webster Pass. The entire drive up to the bottom of the trail, no issues what so ever. Then on the trail again, approximately 20 minutes into it, the engine died again. I came prepared this time and brought several milk jugs full of water. I also brought a contraption to block the hood open a little to help improve air flow. I poured water on the fuel lines, injectors, and the top of the pump. Still it wouldnít start. About 15 minutes later, it started right up.

I decided I would just try getting to the top this way, and sure enough I did. I would drive for about 15-20 minutes and then it would die. I would let it sit for about 10-15 minutes and it would start up again, and I would continue. My engine never over heated and it was a chilly 55 degrees with a little hail and rain, so I doubt vapor lock or temperature was really an issue. To help rule out other issues, I completely disconnected the air filter and was running straight air into the engine.

When I was about 30-40 minutes from the top, it died again. I climbed under the Jeep while I was waiting for the magical 10 minutes to pass, and I noticed the wires from the O2 sensor that plug into the fuel injector assembly had unhooked itself from its mount to the engine. Meaning the cables were still plugged in, but the cables and plug were bouncing around freely under the engine. Thinking the cables or sensor might have failed internally, I unhooked the one sensor. Interestingly enough, the Jeep started right up. I then drove for the next 40 minutes to the top, screwed around a little at the top, and then drove all the way back to Erie without it dying again.

I started to theorize there was some issue with lack of O2 getting to the engine or maybe the failed sensor was giving the wrong signals to the computer and I was getting a bad fuel mixture, but I donít know enough about how all that works. Could it be possible for that one sensor to completely kill the jeepís engine with such consistent precision? I also thought it was very interesting the engine only died going uphill and at elevation. The Jeep never had any issues turning over either. I am also going to check for spark at the plugs this weekend, I just havenít had time this week yet.

If anyone has some ideas or recommendations I would greatly appreciate it. This is the first time I have ever had any issues like this and I desperately would like to get my reliable Jeep in working order again!!!

Thanks in advance for everyone help and I apologize for the long winded post!

My Jeep is a 2001 XJ with approximately 150,000 miles on it. I replaced spark plugs, ignition coil, starter, battery, and A/C compressor within the last 20,000 miles and just replaced the fuel pump. No engine codes to report at this point (except for a disconnected O2 sensor).
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Old September 10th, 2015, 08:57
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thanasi85 thanasi85 is offline
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Location: Sacramento, CA
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Re: Engine Dying Issues - Uphill and at Elevation

In my experience the symptoms you describe are pointing to a issue with your CPS (Crank Shaft Position Sensor). Many times they will get warm an go out causing the engine to just die and then after letting them cool they will work again allowing you to start up no issue. I have had luck with cleaning the connection, and also hosing it down since dirt can build up on them causing them to not give a good reading as the magnet on the flywheel passes by it. Also check that the wires for it have not got to close to exhaust manifold and melted.
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Old September 10th, 2015, 09:30
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ehall ehall is offline
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Re: Engine Dying Issues - Uphill and at Elevation

May be related to changes in the air density. MAP sensor or Air Temperature Sensor may not be working properly at that elevation, resulting in overly rich mixture. Did you try holding the pedal down?
my '91 beater rebuild
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Old September 10th, 2015, 11:10
md21722 md21722 is offline
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Location: Colorado Springs
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Re: Engine Dying Issues - Uphill and at Elevation

My Jeep threw a code for the MAP at the top of Engineer Pass 12,800'. I didn't know at the time what it was but the engine ran fine. I would suspect the crankshaft sensor because of how you are fixing it, letting it sit for 15-20 minutes. Elevation and uphill aren't normally mentioned in problems, usually its folks sitting at traffic lights ready to stall. But going uphill on these trails you aren't moving fast and the engine is making heat... I consider changing the crankshaft sensor every 150,000 or so good preventive maintenance.
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Old September 10th, 2015, 13:26
RaptorXJ RaptorXJ is offline
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Location: New Jersey
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Re: Engine Dying Issues - Uphill and at Elevation

Now my jeep is a 1994 so my ECU not nearly as complicated. I had very similar issues but I never got a code for my MAP sensor (even though OBD1 I still should have) I was just throwing parts at it left and right. Got so tired of it even took it to a shop. They guessed crank sensor. Still nothing. All came back to one night I found a web site to test your MAP sensor. I found out mine was MAP sensor was bad, I never got worse MPG or any other "normal" going bad MAP sensor symptoms, just random shut offs and some times fired back up, sometimes took an hour.

Here is a link to test your MAP
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Old September 10th, 2015, 20:29
ewert35 ewert35 is offline
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Re: Engine Dying Issues - Uphill and at Elevation

I did try holding the peddle down, smelled a little gas at the exhaust, but it wouldn't start still.
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