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Strange Sucking Sound

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304-dude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Sep/29/2018 at 9:54pm
Check your muffler, any rusted out holes will cause like sound. Especially in pipe bends where condensation and mud/ road build up will settle over time. A hidden rust hole out of view will need touchy feely or mirror checked.

I have a bad muffler that eventually will be replaced, it's seems are expanded and rusting away.
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ghcoe Quote  Post ReplyReply Direct Link To This Post Posted: Sep/29/2018 at 10:04pm
New pipe and muffler last spring. No difference...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 9:44am
Try the old trick with an index card.  Bring it up slowly to the end of the exhaust pipe with the engine at idle.  If you are sucking at times, the card will move towards the pipe.
Roger Gazur
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 10:21am
I'd run a compression or leakdown test & see what result you get.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMC Okie Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 11:28am
Smog pump and connections??
69 "GO PACK AMX"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ghcoe Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 11:56am
No smog.

I have done a vacuum test and when it makes the sound the needle does move up and down with the sound. Going by the books it says it is a valve issue. But, that being said as the sound goes away the needle becomes steady.

Doing a compression test I found that 5 and 6 cylinders have low compression. 125 on all other cylinders 80 and 70 on 5 and 6. Did a wet test and compression came up to 125. This means rings going by the books.

There is a noticeable miss until engine starts to warm up then nothing.

No excessive oil consumption. Number 6 plug shows some fuel fouling all others look good. New wires, plugs, cap, rotor, HEI conversion. Still the same issue.

Thanks for all your guys help

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Red Devil Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 12:28pm
Does it have a CTO valve (or two) controlling vacuum relative to temperature?   Maybe low temperature circuit is leaking? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ghcoe Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 1:42pm
Originally posted by Red Devil Red Devil wrote:

Does it have a CTO valve (or two) controlling vacuum relative to temperature?   Maybe low temperature circuit is leaking? 


Nope, all that has been deleted.

I guess I will just continue to drive it and see what happens. Seems like it should be simple. When I figure it out I will report back. Thanks all.
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304-dude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 2:10pm
I have a funny feeling you have a couple of slightly bent or burnt valves. It can allow oil to be sucked into the combustion chamber and darken your plugs, along with loss of compression.
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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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2018 at 9:08pm
When was the PCV valve/hose last replaced and the condition of the oil filler cap/hose?
Also that pesky metal tube running from the choke to the intake. They have a habit of rotting off right at the plate going into the intake and inside the intake. If you still have this. This will make an odd air noise that's hard to "see" because everything still looks to be in place. 


Edited by Trader - Sep/30/2018 at 9:29pm
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