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Rpm's surging at highway speed


Carla G
01-30-2005, 01:49 PM
Hopefully someone can help me. I have read several post and cant seem to find exactly the same problem I am having. I have a 98 Jeep Grand cherokee limited V-8 5.2 L. eng. I purchased it April of 04, and it had 80000 miles on it. There were a few things wrong with it and the dealer fixed all of them, rear bearing and rear main seal leak, ran great after that. Took it to Ann Arbor for Camaro fest in July, no problems. starting noticing gas mileage was deceasing in October. dealer put a new oxygen sensor in it no problems till november. I started noticing this surge in the rpm's one day coming back from the city. It was very noticable because I could feel the jeep pull down as well as see the rpm's go up slightly and then go back down. Took it to the repair dealer machanic again, told him symptoms along with another rear bearing he said he fixed it and cost me $225.00 for what ever he did however it was not fixed. Took it back to him again had him drive it and he noticed it was surging as well. Told me it was prob. the soilenoid or the torque convertor. He said well do the cheaper of the 2 first which h quoted me at soilenoid costing me $40 in parts. I agreed and he did not tell me till after he installed it that the part was actually $174.00. Total cost $300 I was not happy and this did not seem to fix the problem. They even reset the computer hoping to clear up any problems with the transmission? I have no idea what that was going to help and it didn't. Told him it was still surging and he test drove it but of course it won't do it for him. I do not want to take it back to him because he doesn't seem to have a clue whats wrong with it and my pocket book can't take his guessing game. It does it when you hit a bump and it does it when your going up hiil on flats whenever it wants to. usually at 1800rpm it just jumps to 2100rpm's then back down. The problem is getting worse. why is this doing this only on the highway. A friend suggested maybe the fuel pump is going out and about a month or so ago for 2 days whenever I shut off the jeep there was this sound in the rear like a pump shutting down but it just stopped. Can anyone please help me?

dksob81
01-30-2005, 06:52 PM
Surging, sounds like a bad TPS (throttle Position Sensor), The CPS deermines the ammount of fuel delivery to the injectors.

ussually with a bad TPS you would have surging while idling also.

It does sound right about the TCC going in and out of lock-up. But ussually when this happens it's a bad TCC Solenoid. I have the test for the TPS just email me if you would like them

Joe
Dksob81@hotmail.com

jello
04-28-2005, 12:15 PM
I had the same problem on the highway ide be going about 70mph and RPM needle would jump back and forthfrom 2000 rpm to 3000 rpm and could feel the car change in speed, the tranny was slipping and now get slipping in all gears, so Im going to overhaul the tranny seem the foward clutch is worn.

ImChasbo
08-10-2005, 07:39 AM
Now, I believe we're getting close to my symptoms. My 1998 Jeep Grand Cherokee Ltd has a 5.9 litre engine. This erratic surging has been plaguing me for more than a year now and appears to be much worse in the warmer seasons. I began noticing the problem when using the cruise control. The RPMs would increase erratically, almost as if my transmission was slipping. As the problem worsened I began to notice a feeling that the engine was accellerating when I was braking (like a two (2) footed driver). I've been burning through brakes at about every 20,000 miles and I think this is why. Now, I routinely slip her into neutral when approaching a stop. I see this surging often after I've parked. The engine will tach up to as much as 2,000 rpms and could hang there for as long as 15 seconds. I also notice when decending a long hill, at about 1500 to 2000 rpms, throughing it into neutral never reduces the engine speed. In fact it occasionally increases and wou't drop until the ground speed drops significantly. I'm trying to understand the throttle's theory of operation, what components are in the loop, their function, and likelyhood of causing these symptoms. I'll look to Joe for his diagnostic advise but if anyone can help, I'd be forever in your debt.
Chas@Virtuserv.net Thanks - Charlie

89ltd
08-10-2005, 07:58 AM
I would also think about the speed sensor, when they go bad its just as if the tranny is ready to fall out.

tashit
09-09-2005, 08:48 AM
Any luck on finding the problem to this? I have an '01 4.7L with 67,xxx miles and the same thing just started happening to me yesterday. At around 1800 rpm it will jump down to 1700 and then up to 2000-2100 or so and feel like the engine is missing. I also feel a little jerk sometimes around 30 mph when I let off the gas just for a moment. My uncle thought it could be the fuel filter but it sounds like that usually isn't a problem with Jeeps (he's always been a GM guy). Today on my way to work I didn't use overdrive so the engine was around 2700 and it didn't do this at all.

ImChasbo
09-09-2005, 12:12 PM
Any luck on finding the problem to this? I have an '01 4.7L with 67,xxx miles and the same thing just started happening to me yesterday. At around 1800 rpm it will jump down to 1700 and then up to 2000-2100 or so and feel like the engine is missing. I also feel a little jerk sometimes around 30 mph when I let off the gas just for a moment. My uncle thought it could be the fuel filter but it sounds like that usually isn't a problem with Jeeps (he's always been a GM guy). Today on my way to work I didn't use overdrive so the engine was around 2700 and it didn't do this at all.
I did have luck - Please see the thread entitled '99 Grand Cherokee LTD - Engine Racing' and good luck.

tashit
09-12-2005, 12:57 PM
Thanks. My problem was a dirty IAC. I cleaned that and my throttle body since it was already out and my problem is gone. It was a very easy fix!

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