The return of the hiss - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > The return of the hiss

The Original 3/8" Ruffstuff Diff Cover!Building a Bumper?Introducing MONSTALINER™ UV Permanent DIY Roll On Bed Line

Reply
Unread 03-13-2014, 10:54 AM   #1
jbsj33p
Registered User
1993 ZJ 
 
Join Date: Feb 2012
Location: , Virginia
Posts: 205
The return of the hiss

If anyone remembers earlier this year my jeep was making a terrible hissing noise and I thought it was my down pipe flange, well I fixed that leak at the down pipe (thanks everyone) but it turns out that wasn't making the noise. So I figured it was just another exhaust leak somewhere and since I had about had it looking for exhaust leaks I took it in to the shop; big surprise they couldn't find any exhaust leaks either they actually complimented me on how well the exhaust system was put together. Then I went to second shop and a third shop, no leaks, they couldn't all be wrong. The only explanation now is that I don't have an exhaust leak.

The noise:
Sounds like air escaping or being sucked in, like a hiss or an air compressor blower attachment(technical term). It only happens when the engine is loaded up, going up a hill or high rpm, if you drop it in neutral and rev it the hiss is immediately gone. Its not a quiet hiss either, at around 3,000 rpm its louder than my exhaust and engine (I have a flow master super 44)

What I have done so far:
-Replaced all the vacuum-hoses and connectors I could get to
-checked for manifold leaks with my handy dandy spray bottle
-cleaned and inspected throttle body and replaced gaskets
-changed air filter

Nothing has been changed on the engine, no throttle body spacers, no CAI, its all stock.


I haven't noticed any other problems with the jeep, it idles fine and runs smooth it just makes that horrible noise! Help its driving me nuts! :

__________________
Never trust a Jeep that doesn't leak oil.
jbsj33p is offline   Reply With Quote
Unread 03-13-2014, 12:51 PM   #2
speedbucket
Registered User
1993 ZJ 
 
Join Date: Jan 2011
Location: chesapeake, VA
Posts: 3,552
Pcv valve/hose on the side of the intake would be my guess
__________________
http://www.jeepforum.com/forum/f22/speedbuckets-zj-build-1361322/
V8 zj at 6" . Double tri rear and true 3 link front. Stretched to 108"
speedbucket is offline   Reply With Quote
Unread 03-13-2014, 01:00 PM   #3
crouse11c
Registered User
1985 CJ7 
 
Join Date: Oct 2011
Location: Oahu, Hi
Posts: 319
I will start off saying thy ZJ are not in my wheel house and not sure what type of this application you have so this is a wild guess. In my cj I had the same prob and it ended up being a leak in my evap hose to my charcoal canister. If you are in Cali it may have a different setup i hear but mine was as load as my blow off valve in my Mustang. And happened when ever under load of pressure.
crouse11c is offline   Reply With Quote
Unread 03-13-2014, 08:37 PM   #4
Brendan4862
Member
1998 ZJ 
 
Join Date: Aug 2012
Location: , New Hampshire
Posts: 100
It could still be an exhaust leak. I had one once that would only do it under load, because the engine/transmission flexed when accelerating. For me I tightened some exhaust clamps/flanges and it went away.

Food for thought.
__________________
There is no substitute for a Jeep
Brendan4862 is offline   Reply With Quote
Unread 03-13-2014, 09:21 PM   #5
jbsj33p
Registered User
1993 ZJ 
 
Join Date: Feb 2012
Location: , Virginia
Posts: 205
I'll check the pcv stuff out tomorrow and the canister since I will be pulling the bumper to install tow hooks. Could a clogged ccv or pcv cause this? The exhaust leak is still a possibility but I'm tired of looking for exhaust leaks haha so I'm fishing for others ideas to check out. I just wish I could get someone to look under the jeep while I rev it up and stand on the brake.. any volunteers?
__________________
Never trust a Jeep that doesn't leak oil.
jbsj33p is offline   Reply With Quote
Unread 03-13-2014, 11:57 PM   #6
crouse11c
Registered User
1985 CJ7 
 
Join Date: Oct 2011
Location: Oahu, Hi
Posts: 319
Do what I do. 4 jack stands and you can figure a way to accelerate it. Then you can check. But wheels spinning not really under load.
crouse11c is offline   Reply With Quote
Unread 03-14-2014, 10:02 AM   #7
speedbucket
Registered User
1993 ZJ 
 
Join Date: Jan 2011
Location: chesapeake, VA
Posts: 3,552
Quote:
Originally Posted by jbsj33p View Post
I'll check the pcv stuff out tomorrow and the canister since I will be pulling the bumper to install tow hooks. Could a clogged ccv or pcv cause this? The exhaust leak is still a possibility but I'm tired of looking for exhaust leaks haha so I'm fishing for others ideas to check out. I just wish I could get someone to look under the jeep while I rev it up and stand on the brake.. any volunteers?
I had a stuck pcv valve. It literally whistled like a referee
__________________
http://www.jeepforum.com/forum/f22/speedbuckets-zj-build-1361322/
V8 zj at 6" . Double tri rear and true 3 link front. Stretched to 108"
speedbucket is offline   Reply With Quote
Unread 03-14-2014, 10:15 AM   #8
johns1mj
Registered User
1995 ZJ 
 
Join Date: Aug 2013
Location: midland, michigan
Posts: 165
Can you brake torque it and make it happen?
johns1mj is offline   Reply With Quote
Unread 03-14-2014, 10:19 AM   #9
jbsj33p
Registered User
1993 ZJ 
 
Join Date: Feb 2012
Location: , Virginia
Posts: 205
Yep if hold the brakes and give it gas it will make the noise
__________________
Never trust a Jeep that doesn't leak oil.
jbsj33p is offline   Reply With Quote
Unread 03-14-2014, 11:04 AM   #10
johns1mj
Registered User
1995 ZJ 
 
Join Date: Aug 2013
Location: midland, michigan
Posts: 165
Have someone you TRUST brake torque it, preferably in an open area just in case. Spray the engine with water or another non corrosive fluid. If you have a vacuum leak it should suck the water in and change the rpms. At work we dump a large volume of water onto it first. If it responds than we try to pin point the area. An alternate fuel source can be used like brake clean but this is dangerous(fire).
johns1mj is offline   Reply With Quote
Unread 03-16-2014, 10:13 AM   #11
jbsj33p
Registered User
1993 ZJ 
 
Join Date: Feb 2012
Location: , Virginia
Posts: 205
I found someone who would go under the jeep, it was my phone! I got video of the exhaust and had an idea maybe the transmission mount was bad allowing it to move and pull the pipes apart somewhere. But my video shows that the transmission doesn't budge at all neither do any of the exhaust pipes or engine.. clearly those iron man motor mounts work well. Next I looked at the pcv stuff and I'm not sure how its supposed to be but the rear one doesn't have any air flow through it all and the front has a very faint suction, again I don't know if this is how they should be or not. Another interesting thing is when I removed the rear from the intake manifold there wasn't any real change in the way the engine ran, the idle jumped when I pulled it off then settled back to normal, usually with a vacuum line open like that it has a fast or rough idle?
__________________
Never trust a Jeep that doesn't leak oil.
jbsj33p is offline   Reply With Quote
Unread 03-28-2014, 09:19 AM   #12
jbsj33p
Registered User
1993 ZJ 
 
Join Date: Feb 2012
Location: , Virginia
Posts: 205
Back again, I think I've tracked down the noise some more. I had a buddy brake torque it while I looked around the engine bay and it sounds like its coming form the passenger side in the engine compartment towards the front. I don't really think there's anything up there that would make a noise like that, is there?
__________________
Never trust a Jeep that doesn't leak oil.
jbsj33p is offline   Reply With Quote
Unread 03-28-2014, 10:50 AM   #13
HighLonesome
Belief In All Things Jeep
 
HighLonesome's Avatar
1995 ZJ 
 
Join Date: Feb 2005
Location: New Mexico
Posts: 5,380
There is a vacuum line to the reservoir under the battery, but I doubt it would make the noise you describe.
HighLonesome is offline   Reply With Quote
Unread 03-28-2014, 01:16 PM   #14
Gearhead31
Registered User
1995 ZJ 
 
Join Date: Feb 2012
Location: St Pete, Florida
Posts: 1,842
I'm just throwing this out there because I didn't see it mentioned yet, are you positive it's not a weird pulley squeal echoing around? I had an idler doing that, squealing only under engine load on hard accel for some reason, though it wasn't as hidden as your noise seems to be..
Only other things in that area I can think of would be a/c lines and trans fluid lines. I doubt those would be this problem tho
__________________
1995 ZJ ltd, 4.0 i6, *cough stock cough* 253,xxx and still pumping strong
1998 Chevy Cheyenne K1500, 5.7L Vortec, mostly stock
*In peace, sons bury their fathers. In war, fathers bury their sons. - Herodotus
[QUOTE=JasonStebbins]We can call it the Whoosh King Catalog System. :D[/QUOTE]
Gearhead31 is offline   Reply With Quote
Unread 03-28-2014, 01:37 PM   #15
Marcos
Registered User
1993 ZJ 
 
Join Date: Mar 2005
Location: Germantown, MD
Posts: 686
Take the belt off and try it again.
Marcos is offline   Reply With Quote
Reply
Thread Tools






Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.