Hello All, some of you may remember my post here: https://www.ford-trucks.com/forums/1...l-smoking.html where I was trying to figure out the smoke problem my truck was having.

My brother and I performed a compression test and leak down test on the engine. We didn't see anything too crazy until we got to cylinder 5. When we hooked the compression tester up and cranked the engine over the gauge jumped to 60 and immediately dropped to 0 and wouldn't pump back up. We thought it was odd so we tried another gauge and same thing- immediately jumped up and fell back down and wouldn't pump back up no matter how long we cranked for. We performed this test dry and I also squirted some oil in the cylinder and re-tested it. We then found TDC and hooked up the leak down tester and had 40% leak down, which matches the other cylinders in the engine that had the least amount of leak down. We didn't hear any air leaking anywhere.

So this seems pretty weird to me that a cylinder won't show compression, but doesn't leak down and doesn't have air rushing out of anywhere. Two other things we thought was odd is that the spark plug almost looked like it had never really fired, The spark plug was pretty clean except for a little bit of black color on the strap; the other spark plugs had a tanish-black color to them. but I suspected the coil might be bad because coil # 4 was bad and after I replaced it the engine still had a miss.

We tried cranking the engine with the leak down hose threaded into the spark plug hole, but not hooked up to the leak down gauge. It sounded like a locomotive where it had a few light blows and then one strong one when turning the engine over with the starter. We did this same test on a known good cylinder and the good cylinder definitely sounded different from the cylinder in question.

Does anyone know what would make a cylinder not show compression, but check out okay on the leak down test. What should we look for next?

Thanks!

 

Valvetrain Bro!

Leak down test is static, but the compression test is for the dynamic movement.

Check the vale springs and cam(s) under the valve cover. Then the bad news: Use a bore scope next. (Which probably won't help but it will lead you to the next step: remove the head.)

Keep us posted!

 

That's what I was thinking could possibly be the cause, but I didn't really know and I was just guessing. Thanks for letting me know what to check next.

Do you think a problem in the valve train could cause the smoking problem I was having where it would smoke heavily on startup and go away after a couple miles?

Thanks for the help!

 

I can't think of any reason why the smoking would stop.

But then again: I read your other thread and it appears to be coolant- not oil smoke. I suspect your engine will have two separate problems...

Bottom line is that your symptoms point directly at internal mechanical engine failure. Bad news...

You'll have to bite the bullet and get the engine and/or heads out of the truck. Take it to a GOOD engine shop and write them a big check and then you'll live happily ever after.

 

I am also convinced that it's coolant because I've walked through the smoke cloud and it didn't smell like burning oil. I'm thinking it might have a bad head gasket, but am surprised that didn't show up on the leak down test.

If it's just a bad head gasket and the heads need work I'm okay with that and would prefer to keep this short block. If this engine has lower end trouble I think I will be forced to get one out of a junkyard.... I hope it's just a head gasket and head problem, but we'll see I guess.

 

Please keep us posted. And take pics of the cause when you find it.

 

Will do, thanks for the help!

 

Intake valve is closed, and doesn't open.

You might have a cam follower that fell off. It happens on the modulars. Of course, it could be something a lot worse than a follower just "fell off", so be prepared when you take the valve cover off It could be a worn cam lobe or the follower disintegrated.

On the other hand, the fact that you get no compression, but also no leaks when at TDC?

Cracked cylinder. Let's coolant in. When the cylinder heats up, the crack closes up. Drop the piston to half-way or more down after the compression stroke, but not far enough to let the exhaust valve start opening, and do the leak down - with the coolant reservoir cap off and see if any air is going in the cooling system.

On edit: not so sure a cylinder wall crack would close up when the cylinder heats up (from the coolant getting warm). But it does explain all the symptoms. But then, so does a head gasket.

 

Thanks for the info and everything you are saying makes sense. We will try and redo the leak down test with the piston down and see what happens, as long as it doesn't turn the engine over.

Hopefully it's just a follower that's fallen off and a head gasket because if it's a cracked cylinder I'll probably have to shop for a used engine, actually found one out of a van for $600, but it got wrecked really hard and he didn't know how many miles were on it.

 

Looks like you guys were right on the follower being off. Cylinder pumped up to 180, after putting flower back on, but didn't lead to me finding out why its burning coolant when engine is cold.

 

where did it go? did it damage anything?
Is it intake or exhaust?

 

Interesting.

But now it sounds like you have a head gasket leak.

 

It was just laying in the cylinder head. I didn't see any damage, but it's hard to see because it's the last cylinder. It was the intake valve.

 

Is there anyway to tell if I have a head gasket leak for sure? My leak down test results were inconclusive- see image in next post. I've been thinking that it could be an intake gasket leak and I don't know how to test for that so I was considering putting it back together with new intake gaskets and see if it still smokes, but not sure if that's a good idea or not because I would hate to put it back together, it still smoke, and then have to tear it back down again to get the heads off. I was also wondering if it could be a small crack in a cylinder wall as someone else had said and I guess that wouldn't show up on a leakdown test if the crack is lower than the piston. Any advice?


Thanks for the help!