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-   -   Brief rpm increase while driving. (http://www.jeepforum.com/forum/f13/brief-rpm-increase-while-driving-1535779/)

xcaliber81 06-12-2013 08:07 PM

Brief rpm increase while driving.
 
This has been happening randomly since I had my trans leaks sorted out, but while im driving i'll notice a slight increase in my rpm every now and then. Today while driving home i was going 65ish kp/h rpm's were at about 1800 rpm and it briefly increased rpm about 200. Trans is full and fluid is a bit lighter than a maroon color but the atf new was almost the same color new just a bit lighter.

What should i start looking at would this be the engine or trans causing this?

ZeeJay1997 06-12-2013 08:24 PM

this is usually caused by a bad brake switch. to confirm, hold accelerator steady and lightly touch the brake pedal. the rpms should quit cycling.

normal operation is the brake switch deactivates the torque convertor clutch solenoid. this is on a different set of contacts than the brake lights and speed control.

xcaliber81 06-12-2013 11:35 PM

It doesn't always do it though and I have not figured out a pattern yet.

StPaul59 06-12-2013 11:36 PM

Quote:

Originally Posted by xcaliber81 (Post 15555171)
It doesn't always do it though and I have not figured out a pattern yet.

Is it when your cruise control is on? If so you have a bad TPS.

xcaliber81 06-13-2013 08:38 AM

So far everytime its happened I have not been using the cruise.

xcaliber81 06-13-2013 12:46 PM

Ok so watching the tech pump out some fluid today I noticed how dark the fluid was when it came out so if I wanted to do a cheap fluid flush and remove the pressure line and let some fluid out will that work or is there another way so I dont have to buy a gasket again. I just did the atf fluid change but the remander of the fluid that was in there must have darkened up the new stuff. Ive only put 5000 kms on it since the change.

a70eliminator 06-13-2013 02:13 PM

So what advise did you get from the tech?

xcaliber81 06-13-2013 02:22 PM

That I should service it lol duh.

xcaliber81 06-13-2013 02:24 PM

I just dont want to replace another pan gasket because I get trans fluid free and I can do this on saturday if I had some input

a70eliminator 06-13-2013 02:33 PM

Well as already discussed the lock-up-converter recieves input from the brake switch, have you ruled that out?
I had the same issue it's like the trans would slip in and out of OD causing a 100-200 RPM fluctuation, I only then realized I was subconciously riding the brake pedal with the side of my leg. it doesn't take much you barely have to touch it. try it and find out for yourself.

xcaliber81 06-13-2013 03:30 PM

Ill play around on the way home then thanks. But as for the atf change will dissconecting the pressure or return line work to empty out my fluid and how much will come out that way. Enough to make a difference?

xcaliber81 06-13-2013 06:09 PM

So i tried stepping on the brake while driving and was getting no fluctuation. So im not loosing rpm im gaining like 200-300 rpm and its completely random sometimes it will go weeks without doing it and sometimes it will happen multiple times in 1 run. Now that i know the fluid is fairly dark will old fluid cause that kind of behavior?

ZeeJay1997 06-13-2013 06:21 PM

Quote:

Originally Posted by xcaliber81 (Post 15558549)
So i tried stepping on the brake while driving and was getting no fluctuation. So im not loosing rpm im gaining like 200-300 rpm and its completely random

What you are describing are the exact symptoms of a bad brake switch. Think of the TCC as fifth gear. If you drop down a gear at the same acceleration, the RPMS go up. What you need to do is catch it fluctuating and then lightly touch (not "step on") the pedal while holding steady acceleration.

You haven't eliminated the brake switch as cause yet.

If your fluid is dark you need to change it regardless of any perceived problems it may be causing.

qxotic 06-14-2013 02:09 PM

I have the same surge on occasion. I replaced the brake switch but still have the problem. It will do it with or without the cruise on. I have a slow transmission leak but I watch it and keep it within the safe zone. I have not noticed it doing it as frequently since it got warmer.. but it does still happen. Usually on fairly level pavement.. more often I think as I'm entering a curve but not always.

Any ideas?

Thank you,
Daniel

xcaliber81 06-14-2013 04:15 PM

Well I cant be of much help because its so random for me. I wonder if it has something to do with the overdrive itself?


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