2003 Jeep Liberty 3.7l sport has hissing noise from rear

Tiny
DJSPEEDYB
  • MEMBER
  • 2003 JEEP LIBERTY
Every time its started, there is a hissing noise from the rear of the vehicle. It sounds exactly like a fully inflated tire being deflated. But constant. Someone mentioned fuel pump, but it does not sound like a noisy fuel pump. It sound exactly like hissing. Are the fuel tanks on these pressurized? I crawled underneath and it sounds like that where its coming from. I can think of no other place on the back of the vehicle that would require air for operation.
thanks in advance. Steven
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Friday, August 17th, 2007 AT 9:08 PM

10 Replies

Tiny
SERVICE WRITER
  • EXPERT
Hard to say what your hearing, but my first thought is the evaporative system that controls the fuel vapors. The The LDP (leak detection pump) does in fact pressurize the fuel tank. However if there is a leak, it should set the check engine light.
This is the diagram of the system:


http://www.2carpros.com/forum/automotive_pictures/30961_ldp_1.jpg



The LDP is highlighted.

This is the above view of the system:


http://www.2carpros.com/forum/automotive_pictures/30961_ldp2_1.jpg



And a close up:


http://www.2carpros.com/forum/automotive_pictures/30961_ldp3_1.jpg



What we don't know is if this is sucking or blowing air?
Maybe it is sucking from the fresh air filter up by the neck?


http://www.2carpros.com/forum/automotive_pictures/30961_ldp4_1.jpg



#7 is the filter.
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Saturday, August 18th, 2007 AT 6:38 AM
Tiny
SERVICE WRITER
  • EXPERT
BTW, there was a recall on the ball joints for these. MAKE SURE IT WAS DONE! When it lets go, the stud of the ball joint drops dwon and it will act like a flat tire giving you a hard pull. IT wil act like a cutting tip on a lathe as it cuts through and splits your rim in 2.
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Saturday, August 18th, 2007 AT 6:42 AM
Tiny
MARC58
  • MEMBER
I don't have a hissing, but am failing the OBD with a "small leak in the EVS", and I'm trying to find the leak myself. It's a 2003 Liberty.

Your pictures are great, but a little too low resolution for me to see completely. Where did these come from? I didn't see anything about the EVS in Chilton's.

Thanks.
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Monday, August 20th, 2007 AT 9:01 AM
Tiny
SERVICE WRITER
  • EXPERT
Your bet bet is to start off by checking the fuel cap carefully and the neck of the fuel tank. IT has to be tight. IF that isn't the source, your going to need a smoke machine and or a scanner that can operate the evap. System. The tank may need to be dropped to go after this.
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Monday, August 20th, 2007 AT 10:20 AM
Tiny
MARC58
  • MEMBER
Thanks. I swapped the cap with my Caravan. Luckily they're the same. But the problem is still with the Liberty. The neck looks good to me, but I'm no expert either.

I did follow some lines that came down from the filler tube. I'm not sure I followed the right ones, as they disappear for a bit, but it looked, from your picture, like they went into the leak detection pump. A line coming out of that pump is joined by a rubber connection to another line, and that rubber sleeve was split. I gooped it up with Shoe-Goo (the best stuff I had on hand :-)) and am now waiting to see if anything comes of that.

Otherwise, I may leave it to the pros. I'm not a mechanic in any sense of the word and wouldn't know where to rent a smoke machine, nor what to do with it if I could get one. And dropping the tank doesn't look like my kind of fun :-(
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Tuesday, August 21st, 2007 AT 8:07 AM
Tiny
JEEPGIRL311
  • MEMBER
My jeep had this same exact noise- people would stop me to tell me my tire is going down. Really fast! I took it to my jeep dealer, while getting a oil change, and they replaced a vaccum hose, it was a @2.00 part that they did not even charge me for! Wished I knew exactly what hose was called or where it was located-
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Tuesday, August 21st, 2007 AT 2:45 PM
Tiny
WAHNSINN
  • MEMBER
Hi everyone, I have the same problem, the hissing noise and found where it's coming from...but I don't know what it is to replace it. I've circled it here in red. It's a hose coming out of the LDP, and in between that hose and another, there's a black "connector" that is cracked on both ends. When I cover the cracks with my thumb, the hissing all but stops.

If you look at the images uploaded by ServiceWriter, 3rd image, the hose coming out of the LDP on the left near the arrow for #15, follow that to the right and you'll see the "connector".

Anyone know what that "connector" is called?

Thanks!

Tim


http://www.2carpros.com/forum/automotive_pictures/75348_P3260116crop_1.jpg

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Wednesday, March 26th, 2008 AT 12:14 PM
Tiny
SERVICE WRITER
  • EXPERT
I don't know the name of it, but half the time with things of this nature the description leaves much to be desired.

However, by stopping at the dealer and askeing to look at an exploded view at the parts department, they can work with you to point out the particular leaker. This will be a dealer part.
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Wednesday, March 26th, 2008 AT 3:15 PM
Tiny
HAL RAYMOND
  • MEMBER
I have the same hissing sound with my 2007 Jeep Liberty and when I did a smoke tested it (using something that smoked) the smoke was drawn up to the top of my gas tank. I felt around up there and could feel air being drawn but I couldn't find the exact hole. I tried to smoke the fuel filler line and I couldn't keep the smoke contained enough as it was being sucked towards the top of the fuel tank. I guess I'm going to have to drop the fuel tank to find it. There is not enough room to see never mind get your fingers in. Those last photos on mine pass through the frame cross member. This has been going on for a year with a gascap light and a P0456&PD, P0455 recently. Now the engine misfires and diesels when the engine warms up. I have replaced all the hoses and some pipe from the solenoid to the engine and down under near the O2 sensor along with the solenoid at a previous time.
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Thursday, June 9th, 2016 AT 7:24 AM
Tiny
JJ1946
  • MEMBER
My 2002 Jeep Liberty Renegade had the same hissing noise coming from the rear of the vehicle & as others had mentioned, people were frequently saying I had a tire going flat. Ended up being the vacuum line from the engine compartment to the LDP had split. Shop Tech. Found the problem quickly. Thanks for posting info like this to assist others!
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Thursday, October 13th, 2016 AT 9:51 PM

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