2006 f-150 low compression

[gjwickline]

i have a 2006 f-150 with 5.4 3 valve engine with VCT. it has recently had a valve job. it is now in my shop with low compression on left side. particularly #2 and #5 cylinder around 90psi . and cam sensor codes .replaced both cam sensors and one vct solinoid. curious about the mechanical timing. so torn down, removed chain and reinstalled. to insure proper cam timing. It looks to be ok. all links lighned up at marks. the compression is not consistant, as with sticky valves. Main question is If the phasers were not working properly would it have enough effect on cam timing to cause the inconsistant readings

[RahX]

Possibly. Have you done a leak test to see where the compression is going?

[gjwickline]

i have done a leak down with all valves closed on the cylinders. i have not removed the followers yet to perform a proper leak down. it seems as thou the valves are seating properly.

[RahX]

Did you do a dry and wet compression test? Are the followers on those two cylinders installed properly? If it is only low on 2 of the 4 cylinders it has to be something related to those two individually. I would be looking for something easy to mess up. What was the reason for pulling the head in the first place?

[gjwickline]

the valve job was done at another garage. the truck was purchased at an auction. reason for valve job unknown. i removed the cam shaft to do more accurate leakdown. revealed a ring or piston problem. valves sealing properly, pulling engine now to tear down.

[clutch492]

I see that I am 12 years late. But I have to share this.

After going through a nightmare with a 4.6L, I discovered that the intake valve was "cupped" which made the valve stem too long. This would not allow the valve to close completely. A quick fix is to grind off about .50" of the valve stem. Either that, or remove the head and replace the valve. This valve became deformed due to a misfire that created a lot of heat. An intake valve should not be getting that hot since there is air flowing over it all the time. After the compression was restored, the cylinder is firing normally and the valve should not deform any longer. It should last. The only way to get this cylinder to seal, with air pressure in it, was to remove the rocker arm. After measuring other heads, to see how tall the valve stem was, I determined that there was around 50 to 60 thousands of an inch more valve stem on that intake valve. I ground it down, with magnets and rags surrounding it. Put the rocker arm back on, and had compression. Happy Dance!!!