I have been browsing here off an on for a while but haven't had a reason to register or post. So hello all. A bit about myself, I just have a backyard mechanic setup and tool around with stuff amateur style so excuse any lack of keenness on my part.

I'm having issues with a 12 valve engine from a truck I purchased. A little history on the engine. It came from a 94 2500 and supposedly it ran well but had been sitting for 2-3 years and hadn't been started since then. To me assuming it ran well made some sense because it had a bad automatic transmission and when i dropped the pan it was all goodies and roasted fluid, i figured the engine was probably good and for the price i paid it doesn't really matter anyway. I found that the engine appeared pretty clean, full of clean looking used oil but not viscous, thin, or deep black etc. Certainly I realize appearances aren't everything.

I got it fired up on a pallet but found it idled rough, up until maybe 1500-1700 rpm then it smooths right out and sounds good. I have tried all the following with no change.


1. Cleaned Pre-Screen Filter it was really nasty, plus I junk'd the preheater.
2. New fuel filter, old one had a small amt of water in the bottom (5cc) and some gelled fuel
3. Bled all the injectors and lines carefully.
4. New Cummins lift pump and checked the fuel pressure (had on the shelf)
5. New Overflow valve (had on shelf)
6. I did the KDP while it was sitting and checked the injection pump nut torque (to spec)
7. Checked both the feed and return lines thoroughly no restriction or air leaks in either.
8. Valve adjustment to spec.
9. Carefully cleaned and reassembled injectors.
10. Cleaned out the return, injector lines, and banjos with compressed air.

I seem to have isolated the problem to the number 3 and 5 injectors. When they are opened it does not change the idle quality very much. Close them and when you open the throttle and bring it up to 1500-1700 rpm it runs smooth, but as soon as you dip below this it gets rough like its suddenly a 4bt with a couple dead slugs bouncing around. Now if you leave the injectors 3 and 5 cracked open and bring the throttle up it does not smooth out. Its like the injection pump isn't providing enough pressure to open them at low speeds?? Just for kicks I moved the original 3 and 5 injectors after I cleaned them to the front two cylinders and the problem did not follow them.

Other things I noticed/comments.

1. The engine does not seem to have serious blowby or anything. I put my hand over the rear crankcase tube and also clamped it off and opened the oil cap, nothing to write home about. Certainly not a Cummins service test but I think It would be obvious if there was a serious issue.

2. The engine is quiet, no weird noises from the injectors or otherwise.

3. It takes fuel really well and if you stab the throttle you get the expected results.

4. I have not let it run any longer then 3-5 minutes each time and I have not hooked up the charge cooler or radiator.

5. A friend suggested I toss it in the truck i have, hook up the charge cooler and radiator, and run it on the governor for 20 mins

I am thinking perhaps the pump is bad or maybe the timing is off, however i find the timing idea less likely. Any help would be appreciated. I don't know how to check timing so if anyone can point me to a good write up with pictures, and tool recommendations that would be helpful. I do possess the B series Cummins service manuals.