I went out to the garage one morning recently and my ‘88 IROC was making a loud vibrating sound. I think it was the electric fuel pump running (just a guess) though there was no key in the ignition… the battery was on a trickle charger.

I took off the negative battery cable to make it stop.

Any ideas as to what might be wrong?

Has anyone else experienced this?

 

Your gonna need to get a whole lot more specific here......

Generally speaking, if the noise is coming from the back of the car, there are really only two two things back there that could cause this, the fuel pump or the hatch pull down motor. If the noise is coming from the front of the car, the three things off the top of my head would be the electric fan for the radiator, the blower motor for the heat/ac, or the power antenna motor. A fourth possibility could be the wiper motor, but then I'd think you'd see the wiper arms moving as well.

PS, the above advice only applies to a stock, unmodified car. If anyone has installed an aftermarket fuel pump or anything like that, that would be important info to share as well.....

So, in other words, hook the battery back up and follow the sound to it's source, and then come back here and tell us where, exactly, this "loud vibrating sound" is coming from, if we are gonna even begin to be able to help you

 

Without more details, best guess is stuck oil pressure switch.

 

The sound is coming from the right rear, and it’s not as loud as I remembered (I was half awake when I first noticed it). It does sound like the fuel pump.

the rear hatch motor died awhile ago and I have a replacement kit from a guy on another thread.

My mechanic suggested that the fuel pump relay must have failed.

 

More likely the ops is stuck shut as mentioned

 

I had the Oil Pressure Sending unit changed a few years ago because my oil pressure guage was pegged, but it did not solve the guage problem. My temperature guage is also pegged, so maybe there is a broader problem with the guages. Too bad Haynes doesn’t show the locations in their book, but there are lots of YouTube videos.
it has the 5.7 liter engine, only 22,000 miles.

I will do the unplug test and see what happens, once I find out where everything is located.

 

On tpi ops is next to distributor or side of block by oil filter

 

thanks!

I remember it being down where I couldn’t reach it from above the last time I checked. Maybe AutoZone sold me the wrong one before.

 

New info:
I did another test and now realize that the sound is not coming from the right rear of the car but more in the middle, behind the engine, toward the passenger side.

 

Hi kwahamot, The most likely suspect, based on your description of where the sound originates, is the power antenna (if your car has one). My next move would be to unplug the accessories fuse.

In this diagram I found, it appears the power antenna circuit gets it's constant power feed from the accessories fuse, so if you do have a power antenna, pull that fuse and see if the noise stops

 

I think it’s the power antenna.

What relay would fail to allow direct current to that?

 

Hi kwahamot,

It's not usually the relay itself that fails, it's the two switches shown in the diagram in post #10 labeled "Up Down" that are not being properly activated within the power antenna motor unit . You can unplug the relay to stop the antenna motor from continuously running so that you can put the accessories fuse back and have all the other things it provides power to still work (interior lights & so on). If you do a search here you'll find that a certain model of Jeep antenna is a very close match for your failed unit, or perhaps there are places that will rebuild it, I think I recall reading somewhere of a place that rebuilds them (finding a new one is a needle in a haystack proposition, it's been discontinued for quite some time now) . To unplug the relay you will go under the passenger's side dashboard by removing the plastic covers under there, and find the relay with orange, pink, black, white, grey and dark green wires going to it, unplug that and the antenna motor will stop running continuously, then the antenna unit itself will need to be removed and repaired or replaced.

This pic is of a T/A, but it'll be in the same spot on your IROC

 

I pulled that fuse (third row, third column, 20 amps) and the noise stopped! Yay!

Now what to do?

 

Begin the process of removing the power antenna. The plastic inner fender liner has to come out, there will be both a 3 wire wiring connection and the antenna coax connection that feeds the radio signal that'll need to be disconnected, as well as a mounting support bracket along with, of course, the threaded piece you can see at the top of the fender. The antenna coax can be disconnected at the antenna itself, but the three wire connector (that runs the motor), has no disconnect at the antenna, it's wires run through a rubber pass through that's behind the passenger side kick panel and plugs right into the relay. If you want to be able to use the car before you tackle the whole antenna replacement job, you can unplug that connector at the relay and put the fuse back in so that the other stuff on that fuse will still work. Once you get the antenna unit out, the real work of either getting it repaired, or finding a suitable replacement will begin.
Full disclosure; on my car, when it failed (as they ALL always do) I replaced it with a non powered antenna and that was that. Your car sounds much too nice for not trying to get the power antenna working one way or another....

You'll need to unplug the black connector here;


And once you've removed the failed antenna unit, it'll look like this;

(note the screw in connection on the gold colored mast section for the coax, and the black plug at the end of the wires)

 

Thanks OrangeBird and everyone. Great info and support. Great resources!

I’ll dig into the repair/replacement when time and budget allows.

 

If I have more questions down the road, I will post them here or start a new thread.