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Very Low Compression

2004 Lincoln LS 3.0 V6 motor

I did a compression test on my cold motor (does that make a huge difference?) and all cylinders are good except for #1 which reads 60-65 psi dry and 105 psi wet. The ring seems to be shot then, right? Is this to the point that the cylinder will misfire every time? What would be the cheapest way to fix this?

Thanks

Maybe just stuck. Marvel Mystery Oil in the fuel may help, and will do no harm. The engine won’t likely misfire because of this problem. It will lack some power and smoothness. What symptoms have you noticed that led you test compression?

https://www.restoreusa.com/index.php

Tester

I also recommend you try the Restore to see if that helps. I think it will help fix the issue unless there is something wrong with the valves.

I’m looking at additives that might help out, so thank you for the suggestion. My timing chain broke which caused the piston to smack the intake valve on #1 and completely tore up the intake valve seat. I got a new head and cleaned the valves and valve seats up and decided to check the compression on the new head.

Thanks, I heard of Restore before and so I’m hoping it can help out the issue.

Another thing that happened when I checked compression was that cylinder 1 made a sound like “thwup” every time the engine turned over whereas the others didn’t make a sound like that.

Well now, knowing that new information about #1 piston I think I will have to retract my statement about using Restore to help fix the problem. I suspect you may have a bent rod or damaged piston that is causing the problem. Hopefully I am wrong about that.

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Depending on how hard and how fast the valve hit the piston there may be damage that was not visible when the head was off.

Throw a can of Restore in it, it’s certainly cheaper and faster than pulling the oil pan off to inspect the bottom of the piston, connecting rod, etc.

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I have the head off currently and cylinders 1-3 all come pretty much equally flush with the block at each piston’s TDC. Could it still be the rod? The center of the piston took some minor damage and the side of the piston facing the outside edge of the block has a dent as well.

There aren’t any gouges on the cylinder walls and they look pretty good. Could the damage the piston took have led to a faulty piston ring?

It hit while cruising around 1500-1800 rpm I think.
The V6 model LS has the most difficult oil pan design I’ve ever seen, so I’d like to try anything else than pull that thing out lol. I certainly hope Restore could help out.

Can you still see crosshatching on the cylinder walls?

If not, the cylinders are worn.

Tester

There is clear cross-hatching on the walls, it looks just like that picture.

Well there’s your problem, I think.

Aluminum is fairly soft and likely that hit near the cylinder wall may have damaged the top ring groove. If you drop the pan and pull that rod and piston assembly, replace the piston and that set of rings, lightly hone the cylinder wall and re-install. That would fix it.

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Alright then. The dent isn’t on the complete edge of the piston, but I do believe it’s close enough to have caused damage to the ring groove or ring itself. I don’t think I’ll ever try to drop this oil pan so I might just have to live with a weak cylinder if Restore or some other additive can’t help out. Thanks for the info

I tend to disagree . . .

The compression is quite low on this engine

I’ve seen engines misfire that had much higher compression than this one

A few years ago, I worked on an engine that had rather severe misfires on a single cylinder

It had 180psi compression

Sounds pretty good, huh . . . ?!

Well, it was too low

The minimum spec was 210psi

Once the cause of the low compression was resolved, the misfiring was also fixed

You may have possibly broken the top compression ring if the rod isn’t causing the trouble. There really isn’t much else you can do other than removing the piston. You can try the Restore and maybe it will help. You really can’t lose anything by trying it.

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Was that a diesel engine with minimum 210psi? I heard that diesel compression specs are much higher than gas engines.

That’s true. I figure I’ll have to live with a weak cylinder if it doesn’t constantly misfire, I may try using some heavier oil in the mix as well. . .