Low compression and smoke

[hustler900]

I have a 99 f350 that I bought from the original owner for a good price knowing that it had some engine issues. It now has almost 300k miles on it, but had a replacement engine put in by ford under warranty at 100k. The main problem with the truck is that it smokes all the time. Quite a bit of whitish-blue smoke at idle and some more when on the throttle. It changes to a black smoke when at higher rpms and lots of throttle. The truck seems to have decent power and i probly would not suspect anything wrong if not for the smoking, and the truck also has no check engine lights on. So i bought a autoenginuity scan tool to help diagnose the problem. Fuel injectors all sound the same during the injector buzz test. When I did the cylinder contribution test, it said cyl 5 was low. I had also previously done a compression test and cyl 5 was much lower than the rest, around 80psi. So obviously something is wrong in cylinder number 5. My question is, am I getting the smoke because I am burning oil, or could low compression be causing my fuel in cyl number 5 not to burn and create the smoke? I am mainly trying to figure out if the cause of the problem is bad rings/cyl wall, or if it could be a burnt valve or something else. If it only requires me to remove the cylinder head I can d othe work, but I do not have the equipment to pull the entire engine if the rings are bad. Anyone with advice please let me know what you think. Thanks.

[vitalidle]

This is a good one for the techs to answer, but If your #5 cylinder is low on compression your rings could be bad and letting oil blow by the cylinder causing your smoke problems.