Injector problem or something else?

[AlbionWood]

Ford NH 1920 with Shibaura N844 engine, has always started and run smoothly, but just recently began running a little rough, like one cylinder is occasionally missing. Hoped it was just bad fuel or moisture in the sediment bowl, so I cleaned the bowl and drained out the fuel tank, put Seafoam in the sediment bowl and new fuel in the tank. Starts fine and idles fine, but at 1500-2000 rpm it still misses just a little. I tried loosening the injector compression nuts one by one, bleeding each line, but that didn't seem to change anything. The engine isn't misfiring on every revolution, so that operation didn't indicate whether one injector was causing the problem. My question is whether this sounds like a faulty injector, or something else?
If it's an injector problem I will try to get a new set and replace them all at once - they don't look that expensive, the tractor has been cheap to run for many years, and I can't imagine life without it now. But I'd like to know if there is more I can do to diagnose the problem.

 

[hayden]

Fuel filter(s)?

 

[nyone]

I would check compression. but also make sure you can get the injectors out before buying them.

 

[thepumpguysc]

injectors rebuilt/replaced IS the least expensive option.
& a compression test while they’re out is an excellent idea..

 

[AlbionWood]

Fuel filter(s)?

No, I checked, it flows freely. Only has about 80 hours on it.

 

[AlbionWood]

I would check compression. but also make sure you can get the injectors out before buying them.

OK, great suggestions. I have a friend nearby who probably has the compression testing gear. Getting the injectors out might be a chore as they are difficult to access; will probably need to detach the FEL.
If compression is low then it's piston rings?

 

[zzvyb6]

The check valve in the fuel filter bowl is clogged open. When this happens and the fuel tank is not completely full, the pump will start to suck air as a back-flow. Use a vice grips to pinch off this rubber return hose. Then either clean the check valve or cut the air line and block it off.
We cleaned out just about everything out, put in an electric pump and still not enough fuel flow, other than at idle. Pinched off the hose and Bingo ! We have a winner.

 

[AlbionWood]

The check valve in the fuel filter bowl is clogged open. When this happens and the fuel tank is not completely full, the pump will start to suck air as a back-flow. Use a vice grips to pinch off this rubber return hose. Then either clean the check valve or cut the air line and block it off.
We cleaned out just about everything out, put in an electric pump and still not enough fuel flow, other than at idle. Pinched off the hose and Bingo ! We have a winner.

Well I wish that was it, would be a relatively easy fix. But I went out and ran the tractor at 2000 rpm until it started missing, pinched the return hose shut, and nothing changed.

 

[AlbionWood]

Did another round with Seafoam in the sediment bowl, this time after running the tractor fairly hard to get the engine warm. It runs fine on the Seafoam at wide-open throttle, but once that is passed through there is still a little missing/coughing. I think it is better than before though.
I don't see much evidence of a compression problem, it starts fine (almost immediately on turning the key) and idles fine, even at lowest idle speed. Running at full throttle I see no evidence of "blowback" in the PCV tube, and the exhaust isn't particularly smoky.
If the Seafoam treatment doesn't get it running good enough I will try pulling the injectors, bodge an adapter to push carb cleaner through them, and see if that works.

 

[nyone]

Well I wish that was it, would be a relatively easy fix. But I went out and ran the tractor at 2000 rpm until it started missing, pinched the return hose shut, and nothing changed.

You could also put a electric pump on from a fuel jug to test the low pressure fuel system. There fairly cheap and easier than injectors to do.