troubleshooting possible braking issue

[uss2defiant]

Hi all,

Noticed another potential issue with the Jeep.
I'll try to describe the problem as best as I can.

Description:

As I slow the jeep down to a complete stop, right before it halts, the RPM rises a bit, ~50-100 RPM, and I can hear the rev go up. The RPM rises then falls back to previous RPM.
I feel the jeep sort off wants to nudge forward even though I have my foot down on the brake.
If I brake lightly, I can feel that last surge wanting to nudge the jeep forward.
It feels like if I want to stop at point X but instead it stops at X+nudge distance.

I haven't been able to find a leak around the brake booster.

My google-fu hasn't been able to find someone else with a similar issue.

Thoughts/comments?

Thanks!

 

[Hedsic]

If you are seeking an actual surge in the RPM's it's not going to be brake related at all. I don't have an asnwer for you on the issue but I am going to guess it's not the brakes. I bet it just happens to do it when it is almost stopped so it mostly oocurs while you are braking close to a stop.

Possiby something to do with a vacuum line maybe?

 

[Hedsic]

04 jeep liberty 3.7 engine surging - Fixya


See if this helps you any.

 

[LibertyTC]

Sounds like it also could be a sticking IAC plunger.
Remove the IAC torx screw & clean the interior port with carb cleaner & q-tips and use throttle body cleaner to the IAC and get all the carbon off.
Replace IAC and see if that levels the rpm's. IAC controls the idle.

 

[CactusJacked]

As I slow the jeep down to a complete stop, right before it halts, the RPM rises a bit, ~50-100 RPM, and I can hear the rev go up. The RPM rises then falls back to previous RPM.

If you are seeking an actual surge in the RPM's it's not going to be brake related at all.

Actually it can be brake related. A "leaking" brake booster, is losing vacuum. And vacuum leaks can make the engine speed up.
With the engine running, stick your head under the dash and push on the brake pedal. If you hear any kind of a hissing noise, the booster is bad.
If sitting in park and then stepping on the brakes, does the engine still speed up?

 

[tjkj2002]

Since you have the 45RFE it could be the trans downshifting into 1st gear.Mine does it sometimes and has since the day I bought it.

 

[uss2defiant]

Thanks for the replies.
I'll make sure to go through all the suggestions.

Please keep 'em coming if you think of something else.

 

[uss2defiant]

Actually it can be brake related. A "leaking" brake booster, is losing vacuum. And vacuum leaks can make the engine speed up.
With the engine running, stick your head under the dash and push on the brake pedal. If you hear any kind of a hissing noise, the booster is bad.
If sitting in park and then stepping on the brakes, does the engine still speed up?

Does it matter how fast the brake pedal is depressed to hear this hissing now?
While I am pushing it down fast I hear a hiss noise.
This is only when it moves.
I do not hear any other hissing noise while the pedal is depressed.

However, if I slowly depress the pedal I do not hear the hissing sound.


Thanks.

 

[CactusJacked]

You may hear an air sound when pushing the pedal down, that's normal. What's not normal is if you hear a constant hissing noise while you're holding the pedal down, that means the diaphragm is split. By your description, it sounds fine. I take it the brake test at rest didn't affect the idle speed at all?

 

[uss2defiant]

You may hear an air sound when pushing the pedal down, that's normal. What's not normal is if you hear a constant hissing noise while you're holding the pedal down, that means the diaphragm is split. By your description, it sounds fine. I take it the brake test at rest didn't affect the idle speed at all?

ah sorry. forgotten to post about it.

when depressing the brake, the engine's rev does not increase.
It does go up a 100 or 200 then back down to what it was prior after releasing the brake pedal.

 

[Mangate]

I'll go with tjkj on this one. Do you ever get the feeling someone shunted you from behind as you come to a stop?

 

[uss2defiant]

I'll go with tjkj on this one. Do you ever get the feeling someone shunted you from behind as you come to a stop?

Yes. I did notice that if I drove the jeep slow enough and still in 1st gear I do not feel that. I'm kinda leaning towards what tjkj mentioned but I want to also make sure that the brakes are functioning correctly too.

Thanks.

 

[uss2defiant]

hi all,

I finally got to changing the front rotors, calipers and pads last Saturday.
Prior to the fix, I could hear a jinggle-ish sound from both front driver and passenger sides that stopped when the brakes were applied.

However, after the fix, the jinggle-ish sound is still present but not as loud and does not stop when brakes are applied. Don't hear it on the passenger side.

Any clues to what it may be?

Thanks.

 

[John3seventeen]

Front driveshaft cv at the transfer case. Its a common issue usually easy to spot because of torn boot. But check it even if boot isn't torn.

 

[uss2defiant]

ive inspected that before and i know the rear boot needs replacement. the front boot was fine. what do i check for? some play? thanks

also,i checked the hubs while doing the brake job and they werent loose so i think they are fine.

 

[John3seventeen]

ive inspected that before and i know the rear boot needs replacement. the front boot was fine. what do i check for? some play? thanks

also,i checked the hubs while doing the brake job and they werent loose so i think they are fine.

If the boots gone the grease is gone and the cv joint needs replaced. Should eliminate your noise.

 

[CzarKJ]

http://www.jeepkj.com/forum/f202/how-change-front-driveshaft-change-driveshaft-head-47161/ :happy107:

 

[uss2defiant]

kinda hard to imagine that is the issue since i only hear it originating from the front driver side.
ill order the replacement boot kit first. this sure is going to be a PITA to remove.
thanks

 

[CzarKJ]

kinda hard to imagine that is the issue since i only hear it originating from the front driver side.
ill order the replacement boot kit first. this sure is going to be a PITA to remove.
thanks

If you are going to replace the boot you might as well replace the whole thing. Costs 50$ and peace of mind goes a long way. If your boot was torn there is most likely dirt/sand/junk inside that cv now and if it isn't dead already it will be in the near future.

 

[uss2defiant]

oh yeah. that's what I meant. The full replacement. Not just the boot.