Valve Troubles?

[gben00b]

Greetings,

I picked up a 99 XLT/5.4 last week knowing that it was running a little rough. I could not pass it up though as its previous owner literally has OCD and has taken meticulous care over its 200K life thus far – it is mint.

I was throwing 2 codes indicating it was running lean and misfiring on #3. First checked for any obvious vacuum leaks and ran some treatment through it as it had been sitting for a little while prior to my purchasing it. I replaced the coil and plug on 3 but the issue remained. Finally, I had a shop test compression and it appears that #3 is at about half compression. I am surprised considering that it has had all factory services for its entire life thus far. I am thinking/hoping that it is a valve issue and my mechanic concurs.
It has a brand new Trans and most everything else on this truck is close to new so I am not willing to give up on it by any means

Question(s):

1.Do you folks agree with the diagnosis or have any other thoughts on what it could be?

2.If it is in fact the valves, has anyone done a valve job on these? My mechanic said it was likely as simple as replacing a spring that has broken down over time

3.Should I just swap the motor? I can get a 5.4 crate for $2800 brand new and warranted (haven't shopped around much but think this is a decent price).

Any stickys or helpful links would be appreciated as I have been combing this forum for a while and not finding any detail outside of electrical component cleanings and various smaller fixes for this issue.

Thanks much!

 

[toms89]

Add tbsp of oil to that cylinder and redo compression test. If compression comes back up its the rings. Otherwise it is likely the valve(s).

 

[BakerEdition]

First Welcome to the group Glen.....Post some pics once you have some...and Tom...could it be a fuel injector?? I had a car do this once drove me crazy...replaced everything...ended up being a bad spark plug..one of the new one I just put in....my 4.5 cents worth...

 

[toms89]

First Welcome to the group Glen.....Post some pics once you have some...and Tom...could it be a fuel injector?? I had a car do this once drove me crazy...replaced everything...ended up being a bad spark plug..one of the new one I just put in....my 4.5 cents worth...

O.P. said compression test showed low compression in #3. This indicates that is has poor ring seal, leaky valves, blown head gasket or possible mechanical failure somewhere.

Two possible causes I can think of since its been sitting for some time are rings could be siezed to piston or maybe valve in that cylinder was open while sitting and spring is now weak?! Testing compression with oil in cylinder will let you know if it is the ring seal. Go from there..

 

[gben00b]

Thanks for the advice thus far. Mechanic is thinking it is the spring in the valvetrain as well. I don't have the means to do the compression test myself but thats a good tip. If I bet on the spring and start tearing into it, do you know of a thread that can help talk me through it? I'll do some digging on this site and know my way around an engine bay but any help would be greatly appreciated. The quote from the shop included about 4-5 hours of labor to take care of it for me and I would be halfway towards buying a totally new engine if I went that route. Not to mention that might not be the problem.


If I go through the toruble to swap the engine out, it appears I could upgrade to a 12 second expedition based on your signature!