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Strange Sucking Sound |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919 |
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Intake leak between #5 & #7 ?... #5 & #7 fire in sequence... 1-8-4-3-6-5-7-2
so... #5 going down on Intake Stroke & #7 going up on Exhaust Stroke... Intake "suction" manifesting in exhaust pipe during adjoining exhaust stroke...
Uncommon but possible, Intake Mounting Bolts bottom in Head tapped holes BEFORE actually clamping Intake to Heads & sealing intake gasket, maybe... All questions more than a statement... Have seen Intake Bolts bottom out before actually "clamping" intake down to heads... |
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RTTComanche17
AMC Apprentice Joined: Apr/19/2009 Location: California Status: Offline Points: 73 |
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Even though by the book it says it's all leaking past the rings, I'd still do a leakdown test. I concur with 304-dude that there might be some burnt/bent exhaust valves. It really sounds like you engine is being a "pump" and that one of the valves is letting air by when it is "closed".
If you do a leakdown, you should be able to hear the air through the exhaust if it is an exhaust valve leaking. |
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1967 Rambler American #1 - junkyard rescue parts car
1967 Rambler American #2 - project car, but it runs!...for now... |
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232jav3sp
AMC Addicted Joined: Jan/09/2013 Location: Texas Status: Offline Points: 2451 |
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Leak down is the way to go.
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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Just tried to rent a leak down tester. Looks like I will have to purchase a unit since no one rents them. Going to be a few weeks before that happens.
On another note I just got done with a 800 mile trip with the Jeep. Just before I left I went and added 1/2 quart of ATF to see if it would loosen something up. Just did a compression test again. The cylinder that had 70lbs came up to 115lbs. The cylinder that had 80lbs. came up to 105lbs. Not sure if the ATF had anything to do with that or not, but maybe something is unsticking.... |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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You put a 1/2 quart of ATF in the engine oil? (just asking because pouring it slooooooowwwwwllly into the carb is also done from time to time) ^sends some pretty good smoke signals too Sticking rings could def cause low compression, and could be freed up by driving with some a ATF in the pan. I don't know how they could cause the sucking sound tho.
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Remembering the time I ran 12 miles on a dropped valve with a stock 304. There is a lot of clearance in the compression stroke with dished 304 pistons. He may have gummed up valves, from bad seals and carbon build up. Which would cause some valves not to close fully, until enough work and use of ATF loosens it up. Who knows after a few miles the sucking sound will go away. From what i hear 1 quart ATF to a full pan, will clean an engine after a few miles of light driving. |
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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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I might try some ATF down the intake. Not sure why I have not done it yet. Just did this with my daughters Opel earlier this year when she started to shatter rockers...
I really am thinking this is a valve/lifter issue since the sound comes and goes. Over pumped lifters? I will update when I get this figured out. I really was hoping to do a leak down test today. I think you guys are right on with that. |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19676 |
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Never heard of ATF down the intake, but WATER poured down will cut carbon. You have to slowly pour it in and work the throttle to keep the engine running. Could be gummed up rings or carbin buildup on the valves. Water down carb might do the trick... |
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Frank Swygert
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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We've done both water and atf like you said, slowly is the key. I don't advise anyone to do it, I feel it has helped me in some instances, but I wouldn't want to be the reason someone hurt their engine edit the best one was when my cousin came running out of his house with a fire extinguisher because I was at his neighbors house doing it and the street was filling up with smoke
Edited by jpnjim - Oct/13/2018 at 7:14pm |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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ghcoe
AMC Apprentice Joined: Sep/29/2018 Location: SW Idaho Status: Offline Points: 72 |
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Well a rocker broke today on my way out for a day trip. Luckily it went out while still in town. The rocker broke on the exhaust side of the cylinder that I suspected was the issue and one with lower compression. So I guess my thinking is correct in being a valve issue. Now I have to see if I have other problems now. Going to get this worked out if it is the last thing I do.
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