nrk

I'm a new member, long time lurker, hoping to make my first request for help INTELLIGENT.

Bought a 90 Cherokee as a fix-up project and bond with the son over tools (and hopefully do a better job than MY old man).

I have a component under the hood of my 90 Cherokee that is running, and making a bit of a racket, after turning off the ignition. It was running continuously after shutting off the engine (keys removed). It's been a continuous problem since purchasing, and I've needed to leave the battery disconnected to stop the noise. By trial and error I happened across the electrical harness that powered the component and disconnected it.

The harness is at the left (passenger) side of the engine compartment, near the top of the firewall, opposite side of the engine from the master cylinder.

While testing out my new brake lines I installed, I realized that I had poor braking while I left the harness unplugged (and an illuminated BRAKE light lit on the dash). As soon as I re-connected the harness, the BRAKE light went out, and the brakes got normal operability (and resumed the "noise after-key-off" condition.)

Any idea what my problem is? I thought the power brake booster was on the master cylinder, so I didn't think that was the problem, but admit to not having much of a clue.

I'm hoping it's a relay type issue, since it's running after shut off. Any ideas or advice appreciated.

jeepxjho

Well about the only component under the hood that might be giving you this issue since you also said there is a issue with brakes would be the ABS motor.


I would go out to the jeep with the ignition off with the noise going and unplug your ABS relay and ABS fuse from the fuse panel under the hood and see if it quits working.

If so you might have a bad abs motor or relay if removing the relay does stop it i would go pick a new one up or swap it with another realy under the hood real fast to see if it stops with the other relay.

Now if you dont have ABS and you have this noise then i'm lost LOL unless it a electric fan still running.

Willys55

When you say it had poor stopping , did you mean the pedal was real hard to press ? As if it had drum brakes all the way around and no power booster?
I believe this is one of the models that had that stupid electric brake booster. Most times they just failed and you had a rock hard pedal.
Can you tell me what it looks like

jeepxjho

AHHH i forgot about that system here's a write up on how to remove that system if it is bad and to swap back to a normal brake system.

http://www.naxja.org/html/techarticl...ll_OEM_ABS.htm

Willys55

Cool! I was looking for that for him. Awesome Dude.

nrk

...the pedal is easy enough to depress, but it took a bit of pressure at the bottom of the pedal's travel to get it to stop. But, in a word, yeah, like it was operating on drum brakes.

The vehicle's not close by (wish I'd taken a picture under the hood). Although from what I've read in the article in the swap out, i believe it may be the electric booster system described there. I remember seeing brake lines or hoses labeled "brake fluid under high pressure".

Guess I'm screwed, or at least will need to seriously consider the swap procedure described in the article you linked to.

Of course, I'm still going to try disconnecting the fuse and/or relay to see if it stops the noise.

I don't have a manual for the vehicle, any idea which relay and fuse I'm looking for?

Willys55

I remember seeing a post on here about someone helping out with wiring diagrams. When I remember I will send you the link. The best way to find the fuse with out a diagram is to pull one fuse at a time out of the fuse box until you discover the one that is in question, being sure to put each fuse back if not the one. This should help you locate the relay. Sounds like there may be a short to power on the relay causing the relay to remain latched, but relay could be bad as well. Let us know OK.

NickM

If I had to hazard a guess, I would think that the pump relay (mounted on the underside of the bracket for the coolant surge bottle) is stuck.
It should not be receiving voltage to the pressure switch (what triggers that relay) when the key is off.
Try a new relay (this one is pretty beefy, BTW, you can sub a regular relay for test purposes, but don't leave it in).
Operating properly, it should activate the pump when you hit the brakes, then shut off after a couple of seconds (runs for a minute on first start up).

Nick