Strange noise - help!

[HIPCHIP]

90 Ranger XLT 4X4 with 4.0 L V-6. 100K on motor and tranny.

Went wheeling today for the first time in this truck. Pretty easy, fire roads and slow speeds due to washboard.

I start the truck and I now hear a "Thump" sound on the passengers side and it sounds like it's behind the glove box and under the dash. No noise in the engine compartment.

When I shut the engine off, it sounds like "rumbledump".

It kind of sounds like a valve or vent opening when I start the engine, and the valve or vent closing when I shut off the engine. I does it everytime I start and stop. Didn't do it before today after wheeling.

I also believe I heard it when I'm driving down the road as I heard something go "Thump" which I assumed was something moving behind the seat.

I also noticed an oil leak from I believe the tranny right at the bell housing, but that's not where the noise is coming from.

Any ideas?

Thanks all,
Dan'o :}

 

[MAKG]

Perhaps the climate control vacuum motor or outside air door? That's inside the cab, more or less exactly where you describe. Note that they won't move on startup unless the check valve is blown. Then, they see engine vacuum (in max A/C only) on startup.

I've seen the door pop off the vacuum motor before.

Another possibility that comes to mind is air in the heater core, but that seems kinda unlikely not to make sounds under the hood as well.

 

[HIPCHIP]

Perhaps the climate control vacuum motor or outside air door? That's inside the cab, more or less exactly where you describe. Note that they won't move on startup unless the check valve is blown. Then, they see engine vacuum (in max A/C only) on startup.

I've seen the door pop off the vacuum motor before.

Another possibility that comes to mind is air in the heater core, but that seems kinda unlikely not to make sounds under the hood as well.

I'll keep searching around, just don't want to pull everything apart only to find out it was something else, so I'll do some double checking first, but afraid I'll have to yank stuff.

I don't have A/C on this truck, so could this still be a problem?
Thanks,
Dan'o :}

 

[snake]

Yes... the vents still use vacuum and move around. Mine does it occaisionally but sounds like it comes from the right floorboard or maybe forward of that location. Check the vacuum "egg" under the hood (pass side up front but down by the frame) and see if a line got pulled off or rubbed through. Also try to notice where the air is flowing from your vents with the fan on. If it goes to defrost when the defroster isn't on, you've lost vacuum, as it defaults to defrost when the vacuum disappears. Whe the engine is running it may straighten out because there is vacuum present, but no vacuum reservior when the engine is shut off.

 

[HIPCHIP]

Yes... the vents still use vacuum and move around. Mine does it occaisionally but sounds like it comes from the right floorboard or maybe forward of that location. Check the vacuum "egg" under the hood (pass side up front but down by the frame) and see if a line got pulled off or rubbed through. Also try to notice where the air is flowing from your vents with the fan on. If it goes to defrost when the defroster isn't on, you've lost vacuum, as it defaults to defrost when the vacuum disappears. Whe the engine is running it may straighten out because there is vacuum present, but no vacuum reservior when the engine is shut off.

I pulled the under dash cover and started the engine. The thump seems to be coming from under the transmission hump but under the dash area of the hump. When I shut the engine off the rumble seems to come from under the dash but more in the center area. I'll see if I can figure out what you're talking about and give it a good look over.

I checked my trans, and I have a definite leak at the front of the bell housing, so I assume the main seal in the trans blew ( I'm pretty sure it's only trans oil coming out) so don't know if that could be a cause. I'm trying to find a trans shop in my area now.

 

[HIPCHIP]

Between the battery and the airbox, I couldn't see anything down on the frame, but I did check my air and it flows to all the different vents.

 

[skippy]

I pulled the under dash cover and started the engine. The thump seems to be coming from under the transmission hump but under the dash area of the hump. When I shut the engine off the rumble seems to come from under the dash but more in the center area. I'll see if I can figure out what you're talking about and give it a good look over.

I checked my trans, and I have a definite leak at the front of the bell housing, so I assume the main seal in the trans blew ( I'm pretty sure it's only trans oil coming out) so don't know if that could be a cause. I'm trying to find a trans shop in my area now.

trans modulating valve vacuum leak/fluid leak?

 

[HIPCHIP]

trans modulating valve vacuum leak/fluid leak?

I couldn't tell you, I'll see what I can find in the Chilton manual. I don't even know what that stuff is as it's been way too long since I did much wrenching on a car, and I don't know nothin bout no Fords.

I looked underneath at the trans to see if something else was leaking, and all the drips seemed to be only at the bell-housing.

Can you please advise where the trans modulating valve is and I'll definitely check it? Hopefully the Chilton manual has a good description and I'll be able to find it easily.

Thanks for the advice, again, at least it gives me something to check. Looking up prices for trannys is scary. More than I paid for the whole truck!

 

[MAKG]

If this works when idling, remove ALL the vacuum powered parts from the intake manifold except for the fuel pressure regulator, and cap the nipples. If the hiss is gone, reconnect them one by one until it comes back. This will help you isolate.

 

[HIPCHIP]

If this works when idling, remove ALL the vacuum powered parts from the intake manifold except for the fuel pressure regulator, and cap the nipples. If the hiss is gone, reconnect them one by one until it comes back. This will help you isolate.

No hissing sound, just the "Thunk" when I start the motor and the "Rumble" type sound when I shut the motor off. When I was driving home from wheelin yesterday I thought I kept hearing a "Thunk" sound while driving, but I thought it might be something moving behind the seat, but I now think it was the "Thunk" sound that I hear when I start the motor. The "Rumble" sound is much quieter than the "Thunk".

I used to have Datsun and Toyota's, and when you would open the vent for the heat to come out it would make a "thunk" sound, and that's what this reminds me of, but it could also be something thunking the bottom of the trans hump, I really can't locate it for sure. A buddy of mine is supposed to come by tomorrow to help me see if we can figure this thing out. Hopefully I'll have more info tomorrow.

Thanks for all the help folks. I REALLY do appreciate it.

 

[snake]

Modulator valve is toward the rear of the tranny, and will have a vacuum line going to it...

 

[tobey_maguire]

the good one car...!!!
I like it...!!!