I have a 13mm P pump on a 4.1 LPS that will not fire on all the cylinders. When I pull the fuel shut out a little it will fire on all the cylinders and start loping. Any ideas on why it does this? I'm not real familiar with the happenings inside a P pump governor housing. Pump shop that built it really didn't have a great answer for why its doing it. Thanks
This might sound odd but pull your injectors and check them.. If you pulling the shut off you are in essence cutting back fuel, even at idle. If you have an injector sticking or stuck open by pulling the shutoff lowers the fuel going out and might be enough that if one is stuck open the lower amount of fuel will burn and not flood that cylinder putting out the fire in that hole if the shut off was all in.
The thing that I think rules injectors is when the shut is in all the way and rpm is increased to 2000ish with ether the miss is still present. Pull the fuel shutoff a little and it picks up the dead cylinders. I've tried different smaller injectors also.
If it misses with a different set of injectors, all 6 tested at same time in engine. Then i agree, not the injectors. Then your back to looking at the pump and other than pulling it and getting it on a test stand theres not a lot more you can try, Also assuming you dont have anything weird like piston damage from the run you mentioned?
Can we assume at one point it ran smooth, no issues and now this? Did this problem start all at once, slowly over time? Can we also assume your timing didn't slip or any other oddities? Do you have a bore scope or can you borrow one so you can get a look inside without pulling the head? If you can establish theres nothing gone wrong with burnt piston or something like that then your back to pulling the pump and getting it on a test stand and checked.
It possibly could be valve train related also. Bent valve or one out of adjustment, or a rocker issue. One of those without hearing it could be tough to diagnose.
