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Australian Ford Member
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1,120 Posts
Discussion Starter #1
Checked compression on my 119,000km 3.9mpi last night and was pleased with tight motor reading between 1150 and 1190kpa (factory minimum is 1010) until No 6 came in at 950.
Put some oil in and cranked up to 1125, so only possibility I can see is rings, and probably left factory like that as difficult to see why only one cylinder was down. No sign of head gasket leaking in that area or anywhere much else. Exhaust valve in good condition, to extent I could see it through plug hole. Motor was warm but not at operating temperature, so might have influenced it a bit.

I remember testing my 4.1 once with similar results, but there were two adjacent cylinders down and even though oil in cylinder increased compression it turned out to be head gasket as suggested by adjacent cylinders.

Any possibilities other than rings this time round?
 

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Crazed Cone Chaser
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2,524 Posts
EA S said:
Any possibilities other than rings this time round?
I doubt it from what you say.
So far as I know..If the comp goes up after oil = bad rings.

The other guys might have a different opinion though.

Paul.
 

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Australian Ford Member
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1,120 Posts
Discussion Starter #3
Re: Re: Low Compression: Do I have a problem?

(\/)ADXF said:



The other guys might have a different opinion though.

Paul.
I'm hoping.

I should have added that I'm not inclined to do anything about it as it still idles and runs OK.

But is there any point to adding a better cam or doing anything that increases compression with the dodgy cylinder, and will that just make it worse?
 

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need to wary that you dont add too much oil when doing a wet test. If excess oil is added and there is a problem with a valve, the excess oil can actually seal the dud valve.
Cylinder leakage test (compressed air in via adaptor in spark plug hole) is a good one to do in conjunction with compression test.
Pump up the cylinder and listen for air escaping. Ideally, % leakage is obtained using a leakage tester and compared between cylinders but without the right tools you will still get a rough indication of air leaking. (some slight leakage past rings is normal)
 

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Australian Ford Member
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Discussion Starter #5
mbrown42

Thanks.

There might be a ray of sunshine there. I first put a couple of squirts from an oil can in, which I thought should have been enough, and tested it and no change, so I gave it plenty more oil and then it came up. There was enough oil after the second lot to have it thrown up off the top of the piston when cranking and see it on the cylinder walls, and I realised I'd overdone it heaps but didn't think of it sealing valves. Certainly hope it did. I'll get it professionally tested the way you suggested.
 

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Chromed Member
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1,810 Posts
to check headgasket:

get a loan of a pressure tester, connect onto coolant reservior and pump up (obviosly) make sure reservoir is full of water as air lock will give a false reading. Best to leave tester on overnight. Get under car with light and look up between the exhaust and cylinder block for leaks. If pressure stays the same as when you put it on. Everything shoud be A O K!

To check compression:

Remove ALL Plugs.

Disable spark(ie unplug coil or dissy) & fuel

Test each cylinder separetaly with screw in type compression tester.

IMPORTANT- for accurate results HOLD OPEN THROTTLE TO FLAT OUT as you crank engine.

Hope this helps!
:p :eek: :p :eek: ;) :cool: :nuts:
 

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Australian Ford Member
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Discussion Starter #7
Botch

Thanks.

If I can get hold of a tester I'll do it myself the way you suggested. I thought the only way was the way mbrown42 suggested, and that needs air which I don't have.

Didn't know about holding throttle wide open. Is that to ensure full charge of air, or something else?
 

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gone
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10,402 Posts
My EB had the same prob.. all ok bar 1.. sitting at 875... bit of oil fixed it though!

But i decided to pull heads off to have a good look.

BAD MOVE!!!!

Busted 4 bolts in the block cause the bugger before me never used coolant and the block had started to rust inside out!!

Be careful
 
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