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Strange Sucking Sound |
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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Posted: Sep/29/2018 at 11:51am |
Hello, I am writing because I need some help figuring out a strange sucking sound that my engine makes. 360 stock in a 1977 Jeep Cherokee.
The sucking/miss sound has always been there since I installed the motor in my '72 Jeep in '94. Since then the motor moved to the '77 Cherokee in '99. The motor has about 80,000 miles on it now, but after the last trip the noise is much more noticeable now. It sounds as if it is sucking in air on the left exhaust pipe like a misfire or a burnt valve. The strange thing is that it only does it when not under a load. Such as in neutral or park. Once you drop the transmission into drive the sound slowly goes away and the engine sounds normal. Usually it is most noticeable at cold startup and dissipates once the motor comes up to operating temp. Since it is worst now I am trying to figure it out again. Really was not a issue before. Anyone have a idea of what this could be? Thanks, George. |
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AMXFSTBK390
AMC Addicted Joined: Oct/22/2013 Location: SF Bay Area Status: Offline Points: 3489 |
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I have always associated sucking sounds with a vacuum leak. Used Berryman b12 and sprayed it everywhere a vacuum leak could occur. If the RPM dropped I knew I located the vacuum leak.
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Questions are powerful tools...what's in your toolbox?
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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alas, I have tried that. No difference in engine RPM. Sprayed along bottom of carb, along intake manifold and all vacuum related devices. No effect. Unless it is a internal vacuum leak. Sounds like valves though. Can't figure out why it would quit once in gear though.... |
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6PakBee
Supporter of TheAMCForum Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5454 |
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I have no experience with the later AMC V8's but I'll throw this out there. Does your engine have an aspirator tube (about 5/8") that runs from the air cleaner to the exhaust manifold through a check valve? The Mopars that have this feature produce a gurgling sound if the upper hose becomes dislodged from the air cleaner.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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Thanks, but no aspirator tube.
It does have a EGR and a heat riser valve. I am not sure if the heat riser valve is installed properly. Anyone know it the heat riser valve can be installed upside down? To me it looks like the spring load and the weight are working in the same direction. Not sure if this would cause the issue or not though. |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5903 |
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Just to make it easier to see and hear, here's the VIDEO of the sound ghcoe posted: Has the Passenger Side Intake Choke Stove been checked out ? It kinda works with the Exhaust Heat Riser Valve... Choke Stove Internal Tube Hoop maybe has a hole in it ? Heat Riser, this is only a 67-72 Parts Manual Drawing, but may provide orientation clues... The Intake Choke Stove Opening is also visible in this drawing. I have little to no knowledge about EGR function & how / if it might cause the noise. Edited by PHAT69AMX - Sep/30/2018 at 12:15am |
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mmaher94087
AMC Addicted Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1676 |
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Power brakes? Check the rubber grommet on the PB booster.
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Mike
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ramblinrev
Moderator Group Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11468 |
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Good call, Mike!
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74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9081 |
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Also a rusted out air emissions valve will make a hiss, one one each side, mounted on the injection pipe.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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Great responses to what I described. I knew this was going to be hard one to describe properly.
I made a short video of the sound coming out of the exhaust. In the video it sounds more like air escaping rather than sucking. You will hear it come on loud right after I let up on the throttle and slowly dissipate. There is no sound coming from under the hood. This is a cold engine. Usually when it is most noticeable. https://youtu.be/jbzPMUfX6e4 Once warm it goes away for the most part. Hope this helps because I am stumped to what it could be. George. Edited by ghcoe - Sep/29/2018 at 8:45pm |
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