770 Diesel Missing

oliverkid · May 10, 2015

Hey guys. I was working on a 770 Diesel for a friend today and ran into a little issue. They just got the pump and injectors rebuilt and they had me put it all back together for them since this was their first experience with a diesel engine. No problems there, everything went back together like a charm. Got it buttoned back up, gave it a shot of either and it fired right up and picked up all 6 cylinders right away. I pulled it out of the barn to let it run and work the rest of the air out of the injectors and it probably sat their cracked just over an idle for about 15 minutes. It sounded good and didnt see any issues so I pulled the throttle wide open and at full throttle it developes a slight miss on one cylinder. If you take the throttle back under about 3/4 open the miss goes away and it will sit there purring on all 6 agian. I would call it an injector issue but they were all just rebuilt and the shop they went through does dang good work so I trust that they are right. I guess at this point im stumped, anybody else ever seen this???

oliverkid · May 10, 2015

Oh and dont know if it makes a difference or not but its a Roosa Master pump.

Dieseltech · May 10, 2015

Make sure the high speed is set where it should be, if too fast it will have a high speed misfire. Last 880 I worked on needed to be advanced slightly to stop the high speed miss after making sure high speed was right. Don't advance too much or starting ability will suffer..

gordey · May 10, 2015

It might be starving for fuel when wide open,

casecollectorsc · May 10, 2015

Has the valve clearance been checked lately??

hrRoss · May 10, 2015

had same problem when i changed over to roosa master pump, miss would switch to different cylinders. found it was water in fuel after much checking

rrlund · May 11, 2015

That's where I was gonna go. I'd pull the tappet cover and do some checking before I got in to anything else.
When I got my 500 it had a miss. One push rod was out of a lifter. I put it in,adjusted things and started it. It ran perfect for about ten minutes then started to pick up a miss again. The clearance had gone away and I had to adjust it again. Been good every since after the second adjustment.

oliverkid · May 11, 2015

Thanks for the info fellas, I will give this a shot and see where we end up.

Polardiesel · May 16, 2015

Advance the timing.

770 Diesel Missing

oliverkid

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oliverkid

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Dieseltech

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gordey

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casecollectorsc

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hrRoss

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rrlund

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oliverkid

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Polardiesel

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