Mechanics

RPMS DROP AS YOU DRIVE

Jeep Other

Hey everyone,
My wife Jeep is giving me a headache. Its a 99 TJ automatic with a 4.0 that has 110,000 miles on it.
Hope someone here can help. This is going to be long please bear with me I want to give you all the info I can even though it might be to much.
Every morning she uses the remote start (I installed it myself over a year ago). She drives to work (about 45 minutes each way) with no problem, at lunch she goes out to her jeep to have lunch and starts the Jeep and lets it run only long enough to get warm. On her way home (without using the remote start) she gets about 10 minutes down the road and the Jeep RPMs drop down to idle or even lower. It doesn't matter what speed shes going (usually happens on the freeway). Every so often it will die on her. She can start it back up if it dies or if the RPMs only drop down to idle or below within a few seconds it will act normal again. The rest of the way home it will act fine. Once she gets home If I take it out it won't give me a problem. This started about 2 Weeks ago, it happen only once during the first week, the second week it happen almost everyday, and it just happen again today. The days it didn't happen it was raining. I disable (unplugged the whole thing) the remote start the night before the rain day. I thought maybe that was causing it, over the weekend (sprinkling rain) it acted fine. We took it for a long drive over the weekend and by the time we got to where we we going it was dry out, we stayed for about three hours and when we left we got about 10 minutes down the road before it died on us.
Today no rain and it did it again. I did a code scan to it last week and found no codes, I had her leave it running when she got home today so I could do a scan to it again and found no codes again. I tried to duplicate the problem in the driveway and I couldn't get it to happen for me.
I tried unplugging the Idle air control, the speed sensor, throttle position sensor and MAP at different times to see if the RPMs would not increase with the throttle. No luck. The only thing I can think of is the fuel pump or regulator. I can't see that being the problem because if that was it wouldn't it act up at different times not just on her way home. It doesn't make a difference if the tank is at 1/4 or full.
If the rain is solving the problem then what is the rain helping? I even went to different gas stations to get gas for this thing to make sure its not the gas, I also put in a bottle of gas treatment to make sure there is no water in it.
If anyone could give me a clue where to look for the problem I would appreciate it.
Muddy35
Avatar
Muddy35
January 8, 2007.




Now the engine is dying on her when its just parked and having her lunch. Out of the last 12 times the Jeep has acted up it has died on her 4 times.
Muddy35

Tiny
Muddy35
Jan 10, 2007.
I have a 96 Grand Cherokee that was doing the same thing. I changed the Fuel Filter and that solved the problem. Some fuel injected engines have a sensor that increases fuel pressure until the engine warms up. Once warm the pressure drops back to normal. With a dirty filter the pressure drops to low for the engine to maintain idle or run if the filter is bad enough

Tiny
Hawk1_1
Jan 11, 2007.
I put a fuel pressure gauge on it when she got home a few days ago and the pressure was at 49 ( it requires 49.2 +/- 2) I even took it for a drive with the gauge hooked for over 30 minutes and the pressure stayed up there.
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Tiny
Muddy35
Jan 12, 2007.

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