Weak Cylinder on D4 7U (I think 7U)

Your machine is as you said a 5T series.
Do a complete fluid change on the engine including the injector pump housing then give it some hard work for afew hours before worrying about the choof in the engine.

It's a process and you need a special injector socket to remove them but you can install the injector(s) to the lines either pointed straight up or with the lines installed pointing out over the tracks, you can install them pointed down so you can watch them spray by turning the fuel on and off with the throttle or starting and stopping the rotation of the main engine with the pony pinion clutch. I would always keep the decompression lever on START so the engine doesn't run while you're testing. You can also swap injectors or even pumps to isolate the bad component. Keep hands away from injector spray! Diesel injected through skin is a medical emergency for which treatment should be sought asap to avoid gangrene.

Could be injector, pump or some cylinder or head component that's bad. Injector should be easiest to fix, but getting them worked on got a whole lot harder recently when Bill Walter stopped doing them. We REALLY need to get someone else up to speed and doing that or identify shops that can still do the work.

Thanks for the replies.

The engine has gotten several hours of good working, I'd say probably 3-5 hours worth. I've also been running PowerSerivce in the diesel (works well on my diesel trucks). Since I've only diagnosed this #2 cylinder being weak now I can't compare it to previous. It does seem like the occasional kick-in/rev-up is less than it was and the engine running smoother than it did, so maybe after 10 years that 3-5 hours it needs is really more than that. I'll keep working it.

Is there anyone who does work on these anymore or when they're done working am I SOL? Really do love this old machine.

Change the oil in the inj pump, very important...WA7OPY

Change the oil in the inj pump, very important...WA7OPY

I'm pretty sure I did that already. I went through and changed a bunch of oil everywher,e although it would've only run around 3 hours since that.

you can add copious amount of ATF to the oil and warm it up real good then change the oil back to regular. this will in some cases loosen up any stuck rings. it takes quite a bit.