399 head scratcher

Bradiniowa · Nov 24, 2014

Been working on this 399. Has the 1006 engine. Sounds good at low rpms but rev it up and it has a bad miss. Tried several things, had the injector pump checked out, pop tested the injectors, set the valves. Found small problem in the pump, some valves were way off, and injectors checked good. Still sounds the same. Any ideas what to look at next?

Robert Major · Nov 24, 2014

Hi Might sound stupid but have you checked the air filters out, seen a volvo 800 tractor start missing at high rpm and running rough. pulled the filters they were choked to the nuts, and it ran fine with new ones!, have had filters been blown out regular by guys but get that fine dust plug them to, so it may not be obvious at first glance they are plugged, or does a rubber line collapse starving air . Is the timing really right have seen that make a Universal tractor miss at high rpm. Guy moved the pump a fraction and it was ok after.
some timings pretty sensitive on diesels .

Kinda wonder if its starving for fuel or pulling air from the lift pump at high rpm or a plugged injector return might make odd things happen. Have seen comments here from guys about that kinda stuff before, on other tractors. Could there even be a weak or damaged valve spring causing the problem at high rpm .
Thats all I can think others will have ideas to.
Please Let us know what you find.
Regards Robert

Brown Swiss · Nov 25, 2014

Sounds like something plugging the fuel line, or a pin hole in the fuel line!

399 head scratcher

Bradiniowa

Member

Robert Major

Well-known Member

Brown Swiss

Well-known Member

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