Rough Idle, Zero PSI on Cylinder 4

[pxbacher]

94 Ranger XLT V6 4.0 OHV - 223k miles and on its 2nd set of heads

Did the valve cover gaskets last weekend and all seemed fine til driving home from work Tuesday. Just after driving up a short hill, the truck felt rough and sluggish, barely making it over the next hill in the same gear. At idle it runs real rough, and turning the engine over with the coil pack disconnected I get a 1-2-3-4-5-fuh instead of a solid 6-count. Bad news.

So cut to the chase - #4 measures 0 PSI. Before I go tearing into this thing again, any ideas if this could be anything OTHER than a stuck valve? Can a broken spring drop it to zero? Seems like a stuck valve is the most likely, and since I just did the cover gaskets, seems like it's thanks to something I did

Thoughts on this (or how I might have fouled it up) are welcome (sort of).

Thanks

-Pete

 

[adsm08]

Pull the valve cover back off and bump the engine over while watching the #4 valves. If they are moving properly you have a problem in the cylinder.

There are a few other things that can cause 0 psi, most of the ones I can think of, well you would probably have noticed the rod hanging out the side of the block by now.

 

[doorgunner]

 

[adsm08]

Well there are only so many ways to lose that much compression.

I'm guessing he would have noticed the missing spark plug when he went to do the compression test. After that a stuck/sucked valve, a shattered piston, or a broken pin or rod are about all that is left. Usually anything that disconnects the rod from the piston usually lets the rod out the side of the block shortly after.

 

[LearjetMinako]

Well there are only so many ways to lose that much compression.

I'm guessing he would have noticed the missing spark plug when he went to do the compression test. After that a stuck/sucked valve, a shattered piston, or a broken pin or rod are about all that is left. Usually anything that disconnects the rod from the piston usually lets the rod out the side of the block shortly after.

I think the next question should be, "Do you have a connecting rod sticking out of the block's side?".

Here is an idea. Remove the number #4 spark plug and visual check for piston movement. If there is movement, I think we can rule out any CATO damage.

 

[adsm08]

I think the next question should be, "Do you have a connecting rod sticking out of the block's side?".

I'm assuming that's not it, because he posted "It has no power and no compression", not "It sounds like a Farmall with open headers".


Saw a 4.0 SOHC do that on #5 one time. The work order said "Started engine, made a funny sound and then started leaking oil." I started it, it sounded like a farm tractor, so I shut it off quick, pushed it in, and looked around. There was a fist-sized chunk of the block missing right next to the starter.

Here is an idea. Remove the number #4 spark plug and visual check for piston movement. If there is movement, I think we can rule out any CATO damage.

That does work. I skipped it because it's most effective with a bore scope, and the cheapest one I have seen was still about $400 on sale.

 

[pxbacher]

Ummm wow really? What would be sticking out the side of the block?

Ha thanks for the vote of confidence. Last time I blew a CR (70's VW Dasher) the engine sounded just a LITTLE worse than the 1-2-3-4-5-fuh with the coil pack disconnected I'm hearing here Bottom end is sound - this is a top end problem. I'm 99% it's a stuck valve

Can't figure what I did during the cover gasket job that would have caused it - I was super careful not to let anything fall in while I had the covers off...

 

[adsm08]

It could just be a coincidence. I'd still start by pulling the valve cover and cranking the engine over.

It could be as dumb as a collapsed lifter.

 

[pxbacher]

So here's the weirdest part. Drove the truck yesterday and it started rough, but about 5 minutes into my drive I noticed it was running pretty smoothly. At the next stop light it was idling nice and smooth. Seems like whatever was broken or stuck before is now "fixed" (for how long?). Gonna run a compression test on #4 again, and change out the oil and filter before I do anything else...

 

[doorgunner]

Sorry men....but i got a vivid hallucination (meds) when ads_ made the statement about checking for a hole in the block with a rod sticking out....



i just saw it again...........

how bout dumping a bottle of lucas fuel treatment in the gas tank to clean the cylinder innards....