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-   -   Help -- High Pitch Humming Sound in 1991 Wrangler (http://www.wranglerforum.com/f218/help-high-pitch-humming-sound-in-1991-wrangler-41452.html)

JasonB 12-16-2009 04:43 PM

Help -- High Pitch Humming Sound in 1991 Wrangler
 
Hi Guys,

I get this annoying high pitched humming sound in my 1991 Jeep Wrangler (4.0 L, 6 cyl, manual 5 spd). The high pitched sound happens "after" I've been driving for an hour or so at highway speed or an hour or so of offroad driving. :confused::confused: I notice the sound when I've come to a stop. I don't lose power or performance in any way. The engine is not running hot at all. If I kill the engine and start back up in a few minutes the high pitch "hum" is still there immediately. If I let the jeep sit for and hour or so ..... and start it up the hum is gone. It sounds like it's coming from the rear of the vehicle. What's strange is the I get the exact same sound (under the same circumstances) from my '93 Jeep Cherokee, which has the 4.0L, 6 cyl engine but has auto transmission. This "noise" or sound does not happen during short trips in either the wrangler or the cherokee. Sorry guys but the noisy or hum is hard to describe. I've done a lot of "googling" but can't find anything similar to what I've experienced.

This btw has been going on for years..... Neither vehicle has ever left me stranded on a mountain top....


Any ideas???? Thanks much....... Jason

kik 12-16-2009 04:51 PM

When my 89 4.2 5spd had a slight whine sound from the rear, I changed the Dif. fluid and it made a dramatic difference.

JasonB 12-16-2009 05:12 PM

Quote:

Originally Posted by kik (Post 506726)
When my 89 4.2 5spd had a slight whine sound from the rear, I changed the Dif. fluid and it made a dramatic difference.

Thanks kik......... Would you still get the "whine sound" when you were stopped .....and say in neutral?

kik 12-16-2009 06:47 PM

No. The sound must be coming from the engine compartment or trans. because you're not moving. I would suspect more of a trans. problem if you had an automatic. I would start under the hood first, could be external or an internal engine problem. This is a tough one but maybe you can start ruling things out as you go. Good luck.

YjMopower 12-17-2009 12:42 AM

My blazer seems to do this with me to except it goes louder the faster i go. In most cases i just put it in 4wd hi then back to 2 wd hi , the noise goes away. did u ever try changing from 2wd to 4wd when this happens to see if it changes a video would be nice.

JasonB 12-17-2009 07:16 AM

Quote:

Originally Posted by YjMopower (Post 507074)
My blazer seems to do this with me to except it goes louder the faster i go. In most cases i just put it in 4wd hi then back to 2 wd hi , the noise goes away. did u ever try changing from 2wd to 4wd when this happens to see if it changes a video would be nice.

Once the whine or the humm starts it continues no matter what gear I'm in..... hi or low range. I can be in neutral and still hear it. As I said earlier if I kill the engine and let it sit long enough the noise goes away. (If I restart immedately the whine is still there)...:confused:

Again this can happen by a couple of hours of normal "highway" driving.... not just offroad in 4wh or 4wl... And as I said performance isn't affected in anyway....... I'm not mechanical at all, but it seems like as I drive the jeep..... pressure and/or heat builds up and the whine starts from someplace.. and continues even with the vehicle stopped and in neutral...:banghead::banghead:

Short trips (20-30 miles) do not bring out the whine......

RedWrangler 12-17-2009 08:41 AM

and you say this noise comes from the rear of the vehicle? I think I'd drive it around until it was hot enough to start making the noise, then I'd get out and under (carefully) to try to pinpoint the source. It could be some strange exhaust leak that only gets to the whistle poinbt once it's warmed up. Since it continues at idle when you are stopped, you can probably rule out from the tranny back. Does it increase in pitch or loudness with RPMs?

Jaydogg25 12-17-2009 09:15 AM

i have same issue in my 95 wrangler. mine is comming from under hood and starts up about 1min after i start driving then is there whole time i drive. i was thinking maybe vacume leak but cant find the issue. it's driving me nuts. whats strange w/ me is when i give it some gas it will go away (or not as loud) but only for a second, then comes back.

like stated above other than noise i notice no preformance change or anything. i have been just dealing w/ it for now. since looking @ droppin a 350 in mine sometime

morphious 12-17-2009 09:29 AM

sounds like a exhaust leak almost

JasonB 12-17-2009 09:43 AM

Quote:

Originally Posted by RedWrangler (Post 507187)
and you say this noise comes from the rear of the vehicle? I think I'd drive it around until it was hot enough to start making the noise, then I'd get out and under (carefully) to try to pinpoint the source. It could be some strange exhaust leak that only gets to the whistle poinbt once it's warmed up. Since it continues at idle when you are stopped, you can probably rule out from the tranny back. Does it increase in pitch or loudness with RPMs?

Thanks RedWrangler..... When it warms up (it's about 5 degrees here in Colorado at this time..) I'll have to do that. I really don't notice the noise that much when I driving on the highway.... probably because of the tire noise from my BFG A/T's. But when I stop the sound is alive and well.

I don't notice any change in the sound with different RPM's.

This is probably a dumb question but can pressure build up in the gas tank causing the whining noise?........ Thanks again..

morphious 12-17-2009 09:48 AM

not if ur roll over valve is working

RedWrangler 12-17-2009 09:58 AM

I've heard of people having pressure issues in their tanks, but you'd think that would create a fuel delivery issue alongside the noise. Since it seems to remain constant with the change in RPMs though, a fuel pressure issue may be very likely. I would think an exhaust leak would change in pitch with RPMs, as the exhaust pressure would increase as you revved. Have you noticed a large sucking sound when you pop the gas cap? Try this hot and cold. I suppose another possible culprit is the fuel pump itself. Let us know what you discover upon pinpointing the area or better the exact source of the noise, and perhaps we can suggest a good approach to addressing it.

Eagleridge5 12-17-2009 10:29 AM

Sounds like it has to be something with the exhaust when it reaches a certain temperature.

morphious 12-17-2009 10:35 AM

yeah like the cat heats up or something but seeing as he has no performance loss then i don't know

jeepers92 12-17-2009 10:50 AM

x2 on the fuel pump, if sound never changes, and neither does performance, rear of vehicle, moving or non moving, only thing working at the rear of jeep at all times is the fuel pump, that would be my guess when it starts get out and walk around jeep to pinpoint it!

JasonB 12-17-2009 02:10 PM

Thanks for all the replies folks. I don't drive my jeep much in the winter. I may have make a run over to the Moab, UT area just to see if I can get the whine..... If I do I will pop the gas cap just to see it that makes the noise go away.. Wouldn't that be a kick in the rear.......:wavey::wavey:

scott howard 12-17-2009 07:26 PM

When it does it again go to your local oil change place and ask if you can pull over the pit and go down in the pit and take a look.
and if your thinking gas tank pressure just take the cap loose while it is doing it and see if it stops if it does buy a new cap.
hope you find it soon that kind of stuff can drive you nuts

JasonB 12-17-2009 08:28 PM

Quote:

Originally Posted by scott howard (Post 507539)
When it does it again go to your local oil change place and ask if you can pull over the pit and go down in the pit and take a look.
and if your thinking gas tank pressure just take the cap loose while it is doing it and see if it stops if it does buy a new cap.
hope you find it soon that kind of stuff can drive you nuts

Thanks Scott....... The next time I notice it I will definitely take the gas cap off......

BTW, I've made countless trips thru your hometown of WF on my way to Colorado to vacation (I lived in the Dallas area then)..... I've lived in Colorado for many years now...... thanks again.......:wavey:

scott howard 12-17-2009 09:37 PM

Hey Jason, it has not changed any around here..lol
Bet your having a blast with all the snow up that way.

JasonB 12-18-2009 07:07 AM

Quote:

Originally Posted by scott howard (Post 507596)
Hey Jason, it has not changed any around here..lol
Bet your having a blast with all the snow up that way.

The biggest challenge for me when travelling thru WF is trying to figure out which exit to take to grab a burger..... (due to the overpass thru town)

We enjoy the snow a lot.... Didn't see a lot of snow while growing up in central Texas.....:wavey:

GatorDeve86 12-22-2009 08:40 PM

my 92 does the same thing.
i got out and it sounds like its coming from around muffler area

punkafi888 12-23-2009 03:05 AM

first thing you have to note. your driving a jeep wrangler yj. how old is it? exactly. i have squeeks, creaks, thumps, smacks, and a really nice suction sound when i hit about 2k (the air rushing throw the throttle body).

punkafi888 12-23-2009 03:08 AM

also check your tranny fluid, if its a manual change it out to sae60. if its an auto add a flush and change the filter, then add a decent atf3

GatorDeve86 12-23-2009 02:21 PM

Mine sounds kinda like when you leave a compuer moniter on with the computer off that kind of electric humming sound
is that what yours is like?

thechink09 12-23-2009 03:07 PM

im having the exact same problem with my 1994 jeep wrangler. have you been able to come to a conclusion to what it is?


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