This is my first visit to F150 online but looks like a very helpful place. That being said - I need some help. Here are my symptoms:
- white smoke coming out of the tailpipe which lasts for about 2 miles and then goes away (most of time), sometimes it stays for my whole trip and sometimes it comes billowing out. Not sure how much of this is just normal condensation as it has been somewhat cold here in Virginia
- I've convinced myself that the exhaust smells too much like gas, but maybe it smells like water vapor too (No good information here, just saying that I've tried to narrow down my problem by smell)
- My antifreeze reservoir is low - I added up to the lower "cold fill" line 6 days ago and am now sitting about 3/8" below that line.
- I did a compression test on all the cylinders: #1 - 130, #2 - 120, #3 - 120, #4 - 0, #5 - 130, #6 - 115, #7 - 140, #8 - 160. I double and triple checked all of these compressions. #6 was consistently lower than average, #8 was consistently higher than average, and #4 is definitely ZERO.
- Spark plug for #4 may be a little bit black, but not too bad
- Put everything back together with new spark plugs (except for #4) and it definitely sounds like it's missing

I'm thinking a stuck open valve or something like that, but would appreciate any assistance you all may have. Thanks!

 

If the intake follower comes off you will not pull enough air into the cyl to compress giving you a zero compression reading. Another scenario is that either the intake or exhaust valve is bent possibly from a broken valve spring and stuck open and you can't compress air with a valve staying open. The smoke may be coming from unburned raw gas since the injector is still spraying fuel into the cyl. In any of these instances you can get the symptoms you are discribing. You could perform a leakdown test and listen for air leaking either into the intake or into the exhaust manifold but all this will do is tell you which valve (exhaust or intake) is damaged or not damaged. If a follower is off and a valve was not bent then the follower can usually be reinstalled with no problems just make sure the lash adjuster is not broken/collapsed. You say it appears that you are losing coolant. If the head gasket is blown then you wouldn't get zero compression, maybe lower but zero is a stretch. Even if you had enough coolant get in the cyl to hydro lock the cyl and bend a rod you would have low compression but not zero.You may have a bad gasket but the zero compression issue would be the first thing I would investigate. I would remove the cam cover and see what has happened. Just my 2 cents...Good luck

 

I know this thread is over a year old but i was wondering if you ever found/fixed the problem of yours...and what you did.
I also have a 97 and 0 compression in cylinder 4.
I put Marvel Mystery Oil in my gas and oil and it actually seems better...cant tell for sure if it is fixing it or not yet.

 

No amount of oil and fuel additives are going to fix a ZERO compression issue.

 

??
I dont see why it couldnt...for example...carbon build up on valve causing to be stuck...causes 0 compression...oil and fuel additive made to clean out carbon frees up stuck valve...no longer stuck valve...have compression again?
seems logical to me...and its what i have been told.

 

But what would you suggest doing to fix the issue then...if no amount of additives will ever help...

 

I agree with glc. Zero compression and low compression have a few similarites in terms of root cause. Valve leakage for whatever reason will almost always still allow some compression to be generated, unless the valve is gone or severly bent. If you were using multiple compression hoses did you remove the hose from the zero cyl and install a different hose to confirm it's not an equipment issue? Zero compression is possibly a intake valve follower off, a large hole/broken piston, a dropped valve, defective test equipment. Low compression is possibly, debris in valve/seat, damaged seat, hydrolock and bent rod, ring concerns, blown head gasket, sticking valve (bent stem or face), defective test equipment. Probably a few more I'm missing but you get the idea.

 

yes it is a good guage...showed good compression on all other cylinders.
i did a wet test by putting some oil in the spark plug hole to see if that would help temporarily seal the rings...still no compression so yes i assume something with the valves.
I still have no CEL and is running remarkably smooth. I am going to keep running this stuff through there until the weekend where I can do another compression test and see if it has compression now.
maybe I am the lucky one that this stuff just frees up my valve. ha
On my dads motorcycle he had a stuck valve and this stuff freed it up right away and it runs like a champ now.

anyways i figured i would give this stuff a shot before i take off valve covers to get a better look or get a borescope..

 

Id say do a simple leak down test and isolate the problem. A compression test will not tell you whats wrong....only that something is wrong. A leak down test will help to pinpoint the problem as was stated before. Just from what you said about your coolant level dropping so fast I would almost assume a head gasket leak. If you run a leak down test, take off the radiator cap and if you do have a head gasket leak there will be bubbles in the coolant.

 

You can also do a hydrocarbon test on the coolant.

 

another thought/possibility is...pin hole in the piston or the top half of the piston is broken on a ring land....yes they are remote...and a piston cracked on the ring would probably make some noise.

but as others mentioned....most likely valve issuses.

Are you gaining oil level?? from unspent gas washing down the cylinder wall.