D-4 sounds like JD 2-Cylinder Tractor

Try opening up fuel lines one at a time and see if you can pin point which ones are missing and swap them to the good cylinders and see if the miss follows. If so it could be defective spray nozzles.Also take the cover off the side of the ijection pump housing and make sure that the 4 lifters that work the pumps up & down are working as they should and not sticking.It kind of sounds to me like defective nozzle problems.Sometimes they will clear up if you take them to a dealer or inj. shop and have them test them and pump them hard and I,ve seen them clear up doing that.

I was thinking it could be the nozzles...when I break the nut on the injection noozles it causes a little bit more of a miss, but not alot. Its the same on all noozles. I did get some fuel with rust into the system...I bet I done myself in by doing that...will call around and see what it cost to have the injection noozles clean etc..

Take all the nozzles to your dealer and have them checked as it only takes a minute for each one. At the dealer I worked for we didn,t even charge to check those nozzles as at times they needed some new ones anyway so we,d direct them to the parts dept for new ones that tested bad.Sometimes just flushing them out with the pressure of the tester will open them up if plugged with junk but don,t be surprised if it doesn,t as they can,t be taken apart (capsule type) anyway to clean.

well you could go and get them tested or you can call up cat and spend 7 dollars per injector with kit and just get new ones. i do believe that is still the holding price on them. i do know that they are just cheaper to buy them than to get them tested at cat. when i called to get mine tested, they wanted 80 dollars per injector to test them. that was only about 4 years ago.

I have thrown in the towel on this problem:mad

#1 and #4 clyinders seem to be causing the miss..I pulled the injectors, clean them, still causing the problem. Went to Cat and bought two new injectors., still missing. Pulled all the injectors out and cranked over the engine to check for compression on each..no gauge but they are all woofing the same to me.(dont have a compression gauge for a diesel just a gas motor) Moved the injectors around..still the same problem with #1 and #4. Pulled the cover off the injection pump..watch the plungers..all seem to be working just fine..check the fuel flow out of each fuel line at the nozzle..seem to be the same. I ran it for a couple hours a few days ago, and after working it for a while it seem to improve..but still a noticably miss. Like I said earlier in my post this motor purred when I first got it. I did run some fuel with some rust in😞 ..but by now I think I would have it all cleaned out. The only thing left would be I guess a complete compression check and see if I dont have low compression on those two clyinders...anybody else got any ideas..I sure would apppreciate some...thanks

What is the Sn?

Get a leak down tester and check for leakage. My precombustion chambers have pipe thread in them so I made an adapter to fit. Here is a leak down tester. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=94190

Maybe you have some bad valve springs.

my buddy had the same problem only all the injectors were clogged. but i had to run a test on them to find out. try pulling the new injectors out the machine, connect the lines up to the injectors outside the machine. connect the lines from the injector pump and to the nozzel and start the pony motor. turn the big motor over and open the throttle up with the compression release off so you are not trying to start the diesel engine. see if you have a mist coming out the nozzels or not. if no, then there is something wrong at the pump. if you do have a mist coming out, then you might have something wrong within the engine.

I don't believe I read where you moved any of the injection pumps around....try that, may be a problem with one or more of the pumps.....I'm thinking check valve....susceptible to dirt but seldom suspected😊

i think s j is on the right path take the cover off the side of the injector pump make shure all the pistions in the pump are free i brought a d 4 home a few years back the pump was well oiled but it was sticking and we had a miss we lousend it up and it ran like a cat agean/.