Compression numbers

[OldIron82]

Hello everyone. After almost a year I am still trying to hunt down this partial miss.
I thought it was a lazy lifter, so I replaced all 16. Also checked all the push rods, nothing bent. Most recently I did a compression test, and here you will find the numbers. The injectors are only two years old, and the injection pump I bought a brand new 100cc from a very reputable builder from here. I am seriously at a loss of where to go from here. I don’t know if you can have a weak port on a injection pump?
The worst part of this situation is the miss varies in intensity. Some days it’s barely noticeable, other days it’s very pronounced. Now that winter is setting in its a total dead cylinder on cold mornings and smokes horribly, then suddenly the cylinder wakes up and it’s back to the partial miss.

My thoughts are to swap injection pumps, and do a leak down test. I can only think it’s fuel problem or some kind of valve problem.

Thanks

 

[Shadetreemechanic]

Its most likely an injector. I would take them out and pop test them, If its not that it may be the engine itself. Your compression numbers are high enough, but they have a lot of variability. You want your compression# to all be within 10% of each other for a smooth running engine. Yours vary by more than 20%

 

[OldIron82]

Thank you

 

[Big Bart]

Some thoughts-

Shadetree is correct a injector pressure test is in order. It might also shine some light when you see the injector tips.(Sooty, oily, clean, dirty, leaking past the copper seal, etc.) But your injectors should pop around the same PSI and spray/atomize nicely.

Fords only guidance on compression testing was no two cylinders more than 20% different. So you are right around there. But 350 psi is pushing the lower end of the scale.

Since you have more issues when cold perhaps do the following.
1) Check your glowplugs. If a couple don’t work that might be your cold wake up issue.
2) Try doing a compression test on a cold morning on the two cylinders that are 350psi. Perhaps they are lower stone cold. Thus they improve as the warm up.
3) Crack the injector lines open on a cold morning. Try to determine which cylinder/cylinders add the least power. (Make the smallest change when the injector line is loosened.). Cover the line with a rag and wear safety glasses.
4) Do a leak down test when cold on the cylinders that had least power. See if you can determine if a valve or ring issue.

But keep in mind these engines will run for years on low compression or a couple low cylinders. So you can roll as is or rebuild if you like a good project. The challenge right now is parts availability so perhaps run as is for 12 months and do a rebuild as parts become more available.