4020 runs rough/misses

I have a 64 4020 diesel that has had the original engine swapped for another 404 from I believe a 7700 combine (naturally aspirated) several years ago. The tractor has always run good and had good power I do some disking with it and planting but it rarely gets over 100 hours a year put on it. A few years ago it started running rough and what sounds like missing, I was pretty well done with my spring work when it started so I parked it in the shed and because I have other tractors and not much free time I just haven't used it much the past year or 2 now this year I'm going to need it and want to fix it. I had some time to work on it this morning and cleaned it sediment bowl on the lift pump replaced the filter and bled the fuel lines at the injectors all with no change. I'm wondering if there is a way to test individual injectors (pencil type) while still on the tractor and how to know if the injection pump needs rebuilt/ replaced it seemed like the injector lines were really "hammering" while it was running and my 4320 doesn't do that. Also wondering if i could rebuild the injector pump myself or if alot of special tools are needed?Any advice will be appreciated. Sorry for the long winded post just wanting to give you fine folks all the information I can. Thanks in advance.

To my knowledge the only way to check injectors is with an inj tester that checks pop-off pressure and one visually inspects spray pattern and for drips. Have you tried advancing the timing a few degrees?

I have read about timing advances some on this forum and
had wondered about that myself. In this case I assume you
mean to advance it by turning the pump on the mounting
bolts/slots? Is this best done with the tractor running/listening
for the right advance or to open the timing windows and set it
that way? I will have some more time today and will check
where the timing is set and post back. Thank you

Yes altering timing by slightly turning inj pump. I've accomplished this in the past with engine running while some tech's on this forum advise to do with engine stopped.

I would start the tractor and run it at the rpm the miss is most pronounced. Then slightly loosen each injector line one at a time at the injector connection. The injector that doesn't affect the engine rpm at that time has problems. Then maybe all you have to do is replace one injector.

Adrian

Could it be a mechanical problem rather than fuel injection? Perhaps a rocker arm has broken or jumped off, or a valve has hung open a bit and so one cylinder can not move air or burn completely. Have you pulled the valve cover?

Paul
You are correct the miss could be a valve not opening properly due to a faulty rocker arm. It wouldn't bee the first 4020 for this to happen to.

Thanks for all the input I did pull the rocker cover and everything looks good and I did crack the injector lines with the tractor at idle and it seems to be an intermittent miss as no line particularly improved or worsened the problem so I pulled all the injectors hoping to see an obvious problem and they are carboned up on the tips some so maybe they just need a good cleaning but I'll probably take them and have them tested Monday anyway will post back with the results. Thanks again for all the quick and helpful info.

Thanks for all the input I did pull the rocker cover and everything looks good and I did crack the injector lines with the tractor at idle and it seems to be an intermittent miss as no line particularly improved or worsened the problem so I pulled all the injectors hoping to see an obvious problem and they are carboned up on the tips some so maybe they just need a good cleaning but I'll probably take them and have them tested Monday anyway will post back with the results. Thanks again for all the quick and helpful info.

Same issue on 4020, some bad injectors. I would pull pump and injectors, take to shop for testing.