05 F250 Excessive blow-by.... why?

[tunedportcj5]

I did do the WOT test and all of the plugs looked the same. All clean burning but slightly wet.

Here are my tests at 100psi

Leakdown test @100psi
1-95psi, compression 190psi
2-93psi, compression 190psi
3-97psi, compression 195psi
4-95psi, compression 192psi
5-96psi, compression 190psi
6-95psi, compression 190psi

93=7%
94=6%
95=5%
96=4%
97=3%

[pstephens46]

Do you have any way to scope the bores as Boscoe suggested? Looking for bad patches down below?

[tunedportcj5]

Do you have any way to scope the bores as Boscoe suggested? Looking for bad patches down below?

Not at this time. I can get one though...

[tunedportcj5]

Fixed!!!!!!

Since 9 out of 10 threads on here (and everywhere else) never post up a resolution on these crazy issues. I figured I would update you guys...

There is definitely something strange with some of the '05 F250s and Yamaha did in fact make a kit to resolve the crankcase vent from spewing oil into the intake box at high RPM. Yamaha calls it a "Anti-Purge Kit".

As crazy at it seems, this has fixed my problem.

This has been discontinued by Yamaha and no longer produced... but I got lucky knowing the right people. The PN is 90891-40625. This kit can easily be duplicated however...

Hope this helps other folks with the same problem!

Thanks everyone for their troubleshooting support!

[99yam40]

Thanks for coming back and letting us know what fixed it.
very strange problem