DodgeMan Posted February 19, 2012 Share Posted February 19, 2012 I was working on my B81 again, it runs fine at mid to high rpm. Dosnt really want to run good at slow rpm or at a idle. And only starts with a little help from a can of either.I changed the fuel filter, and fixed the valves in the primer pump. Buids pressure better but still not the best.Going to replace it with a new one.Anyone have any ideas on anything else it could be??Thanks Paul Quote Link to comment Share on other sites More sharing options...
Rob Posted February 19, 2012 Share Posted February 19, 2012 I was working on my B81 again, it runs fine at mid to high rpm. Dosnt really want to run good at slow rpm or at a idle. And only starts with a little help from a can of either.I changed the fuel filter, and fixed the valves in the primer pump. Buids pressure better but still not the best.Going to replace it with a new one.Anyone have any ideas on anything else it could be??Thanks PaulTry advancing the timing a slight bit. Has the pump been off the engine? Do you know the timing is correct? Have you pulled any load with the truck?Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
fifth wheel Posted February 20, 2012 Share Posted February 20, 2012 Weak transfer pump or sucking air somewhere.FW Quote Link to comment Share on other sites More sharing options...
DodgeMan Posted February 22, 2012 Author Share Posted February 22, 2012 Transfer pump pressure is very low, got 2 pumps on order. Going to check the timing this week some time just incase. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted February 22, 2012 Share Posted February 22, 2012 Try advancing the timing a slight bit. Has the pump been off the engine? Do you know the timing is correct? Have you pulled any load with the truck?Rob What he said then you can rule out the fuel pressure problem and air in fuel then move on to maybe bad injectors or something else. Quote glenn akers Link to comment Share on other sites More sharing options...
DodgeMan Posted February 29, 2012 Author Share Posted February 29, 2012 Transfer pump took care of the fuel pressure problem. Idles better and runs smoother.Still only starts with either, even after it warmed up. Will check the timing this weekend if i get a chance. It doesn't look like the pump was ever off the truck or screwed with, all tho slow idle seams to be set real low, engine dies if i take my foot totally off the pedal or there's a problem with the pump its self. Quote Link to comment Share on other sites More sharing options...
Rob Posted February 29, 2012 Share Posted February 29, 2012 Transfer pump took care of the fuel pressure problem. Idles better and runs smoother.Still only starts with either, even after it warmed up. Will check the timing this weekend if i get a chance. It doesn't look like the pump was ever off the truck or screwed with, all tho slow idle seams to be set real low, engine dies if i take my foot totally off the pedal or there's a problem with the pump its self.It almost sounds like the pump's plungers and barrels are worn out. Advancing the engine dynamic timing with cause the injection cycle to begin sooner as the piston rises in the bore slightly compensating for the lack of fuel at the proper time when set correctly. This is not a cure, only a troubleshooting aid. You would be well served to pull the pump and get it and the injectors into a shop to have it checked and/or repaired.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
DodgeMan Posted March 20, 2012 Author Share Posted March 20, 2012 I built one pump out of 2. I used my gov off my truck and a old pump off my dads druck that worked when we pulled it off.Took care of the problem and it runs great. Quote Link to comment Share on other sites More sharing options...
Rob Posted March 20, 2012 Share Posted March 20, 2012 I built one pump out of 2. I used my gov off my truck and a old pump off my dads druck that worked when we pulled it off.Took care of the problem and it runs great. I'd still send it in for correct calibration. Seat of the pants is not the best thing with diesels.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
DodgeMan Posted March 20, 2012 Author Share Posted March 20, 2012 i used all the factory mack gauges and specs to calibrate the pump. prob will send my old pump out for rebuilding.thanks for your help rob Quote Link to comment Share on other sites More sharing options...
mackman55 Posted March 20, 2012 Share Posted March 20, 2012 Check your fuel lines if they are old they might be sucking shut it has happen to me and they were the last thing i check it drove me nuts. Quote Link to comment Share on other sites More sharing options...
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