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94 Explorer Rear Noise

3Dee

Member
Joined
May 15, 2020
Messages
19
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City, State
Guernsey
Year, Model & Trim Level
1994 Ford Explorer XLT
First post on here, hello everyone! I look forward to using the forums with you all.

Just recently bought a '94 explorer 4x4. The drive home was as quiet as can be. But this morning, theres a new high pitched, drill like sound (or a hydraulic lift or something, idk) coming from behind the rear wheel wells. Was wondering if anyone knows what this is, and possibly how to fix it. Thanks.
Here is a video of the sound
 



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Well, let's see if we can nail it down as the fuel pump first. If you were to turn the key to ON but not START, do you hear the same sound for a second?

If so, then it's the pump, or at least related to it. I wonder if the noise changes for a full tank versus empty... how full is it now?

Yeah, if it's the pump, it must be contacting the tank in some kind of way internally, and I would investigate that. You can drop the tank or cut an access panel... there's threads on here for both.
 






Well, let's see if we can nail it down as the fuel pump first. If you were to turn the key to ON but not START, do you hear the same sound for a second?

If so, then it's the pump, or at least related to it. I wonder if the noise changes for a full tank versus empty... how full is it now?

Yeah, if it's the pump, it must be contacting the tank in some kind of way internally, and I would investigate that. You can drop the tank or cut an access panel... there's threads on here for both.
When I turn it to ON, I hear a quick low buzz from the fuel pump, but it stops after a second. The high pitched sound starts a few seconds after I start the engine.

Also, the tank is completely full. I took it to the gas station this morning because I thought that it could be low, but it only took 3.1 more gallons to fill it.
 












Does the sound change with engine speed? I really have no idea what that might be, I'm just sifting for a clue!
I'm pretty sure the sound persists when driving, but the engine covers that noise.
 






I think you are going to have to get under, around, inside, etc... and see if you can hunt it down. You know what this could be, which would be really strange, but open the back hatch and the open the left panel where the jack is stored and see if it's louder in there. Or... try to use the rear window washer. I mean, this is really a stretch, but if your washer pump were stuck running for some reason, it makes that kind of sound.
 






I think you are going to have to get under, around, inside, etc... and see if you can hunt it down. You know what this could be, which would be really strange, but open the back hatch and the open the left panel where the jack is stored and see if it's louder in there. Or... try to use the rear window washer. I mean, this is really a stretch, but if your washer pump were stuck running for some reason, it makes that kind of sound.
When I saw this, I instantly had to see if it was the problem, but unfortunately, the wiper washer works just fine, and the sound still remains directly under the back of the vehicle. Tomorrow is my Graduation, but if I have time, I'll check under there and see if I can find the source.

The wiper noise and Another video under the explorer
 












If it were parked, as you show, and you bump the throttle, does the sound change?
No, it stays the same. Also it can only be heard from the drivers side.
 






I think it must be either some unknown third-party gizmo mounted under there somewhere or...

The fuel pump. I really don't know how a fuel pump could make that noise so loud, immersed in gasoline, inside a plastic fuel tank. But, that pitch is what I would expect if I ran a fuel pump dry on a bench. It would be great to figure out a way to rule in/out the pump without actually replacing it. Maybe it's a bad bearing in the pump motor and it needs to run a little bit to get up to that pitch of noise.

Ok, let's run through this and make sure we are on the same page:
1) You turn the key to ON, and you hear the fuel pump run for about one second. It's a brief lower-pitched noise.
2) With the key ON with the engine not running, you do not hear the higher-pitched noise, even if you leave it like that for a minute.
3) You start the engine, and you begin getting the high pitched noise immediately.

If all of these are true, then maybe we can make the noise happen by running the pump continuously with the engine off, and if we can, then we can relate the noise to the fuel pump.

If that sounds reasonable, you could do the following:
1) Locate the OBD I connector, it is loose behind the power distribution box (fuses and relays) under the hood. Or it may be clipped to the back of the box itself. It looks like this:
OBD_photo.jpg


2) One of those connectors manually triggers the fuel pump. Here is a diagram:
OBD_pinout.gif


3) Connect the connection labelled 'Fuel Pump' to ground. Ground please, not +12V... +12V would do bad things, it needs to be grounded.

4) In this condition, turning the key to 'ON' without actually starting the engine will cause the pump to run continuously. Turn the key to 'ON' without starting the engine and leave it like that for a minute. Do you get the noise? Can you control the noise by turning the key OFF and ON? If you remove the ground from the connector and do the same thing, does the noise not happen? That would be diagnostic proof that the noise is coming from the fuel pump.

Do not leave the pump running with the engine off for too long, just a minute or so. If you have a leaky fuel injector, it could start filling a cylinder with raw fuel. If you want to do this repeatedly, start the engine for a moment, stop it and try the test again. It's unlikely you actually have a leaky injector, but I just want to cover all the bases.

If this does not create the high pitched noise, I don't think it rules out the fuel pump definitely, it's just a test that might prove it IS the pump.

Anyway, I appreciate that you just graduated, congratulations by the way, and your time may be tight right now. Whenever you get to it, if you want to give it a shot.

Good Luck!
 






I think it must be either some unknown third-party gizmo mounted under there somewhere or...

The fuel pump. I really don't know how a fuel pump could make that noise so loud, immersed in gasoline, inside a plastic fuel tank. But, that pitch is what I would expect if I ran a fuel pump dry on a bench. It would be great to figure out a way to rule in/out the pump without actually replacing it. Maybe it's a bad bearing in the pump motor and it needs to run a little bit to get up to that pitch of noise.

Ok, let's run through this and make sure we are on the same page:
1) You turn the key to ON, and you hear the fuel pump run for about one second. It's a brief lower-pitched noise.
2) With the key ON with the engine not running, you do not hear the higher-pitched noise, even if you leave it like that for a minute.
3) You start the engine, and you begin getting the high pitched noise immediately.

If all of these are true, then maybe we can make the noise happen by running the pump continuously with the engine off, and if we can, then we can relate the noise to the fuel pump.

If that sounds reasonable, you could do the following:
1) Locate the OBD I connector, it is loose behind the power distribution box (fuses and relays) under the hood. Or it may be clipped to the back of the box itself. It looks like this:
View attachment 316337

2) One of those connectors manually triggers the fuel pump. Here is a diagram:
View attachment 316338

3) Connect the connection labelled 'Fuel Pump' to ground. Ground please, not +12V... +12V would do bad things, it needs to be grounded.

4) In this condition, turning the key to 'ON' without actually starting the engine will cause the pump to run continuously. Turn the key to 'ON' without starting the engine and leave it like that for a minute. Do you get the noise? Can you control the noise by turning the key OFF and ON? If you remove the ground from the connector and do the same thing, does the noise not happen? That would be diagnostic proof that the noise is coming from the fuel pump.

Do not leave the pump running with the engine off for too long, just a minute or so. If you have a leaky fuel injector, it could start filling a cylinder with raw fuel. If you want to do this repeatedly, start the engine for a moment, stop it and try the test again. It's unlikely you actually have a leaky injector, but I just want to cover all the bases.

If this does not create the high pitched noise, I don't think it rules out the fuel pump definitely, it's just a test that might prove it IS the pump.

Anyway, I appreciate that you just graduated, congratulations by the way, and your time may be tight right now. Whenever you get to it, if you want to give it a shot.

Good Luck!
Good news! I think the issue was the fuel level being too high, as I'm now lower than full and the sound is barely noticeable! Thanks so much for all your help! Again, I look forwards to talking with you all!
 






Well, it looks like the problem was something different. After the noise came back a few days later, I became increasingly confused. I took another look under the explorer and there was something I hadn't noticed. Sure enough, my muffler has a hole from rust. I should've seen this sooner, but I guess it's good to know where the problem really is.

Is there a thread with some info on replacing the exhaust system? And some wisdom on where to look for the parts?
 

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