Turning an injection pump

[1bad383]

How hard should it to turn an injection pump, installed on an engine & full of fuel. Have clear line temp installed, and can turn the pump with three fingers fairly easily, feeling the vanes in the pump going over the various ports. But cannot see the fuel moving... There is ONE air bubble in the line. So I took the front end apart to make sure the timing was correct (dot to dot) on the timing gear and pump, it was. Still trying to figure out why the thing white smokes as bad as it does. It has even compression, turning the motor over by hand on the crank. It it possible some way some how that the injection pump is causing the smoking problem, even with the timing as perfect as I can get it? Two things I can rule out, compression and physical timing. New motor & injectors. That leads me to the pump next?!!? There no body in town, that I can find, that has even a slight clue as to how these motors work! The Diesel Page has really been helping me out!

[JohnC]

The electronic pump won't pump unless the electronics are working. Since it isn't pumping, it isn't hard to turn.

[Warren96]

The clear line should have 1 bubble in it,as long as it dosen't look like it is BUBBLING,like a soda bottle. By the way, mine didn't smoke when it had air in the return line. It had stumbling and starting issues. At one time it did have a visible smoke problem, but not at idle. If I remember correctly, on another thread didn't you say it smoked visibly at warm idle?

[Kenneth]

Insufficient fuel can cause white smoke. So, yeah maybe your injector pump isn't supplying enough pressure and/or volume to the injectors. Check to see if there is any fuel being returned to the injector pump. If not, it may mean that there is insufficient fuel supply to the motor. I realize gasolines engines are different, but on return-type fuel systems on gasoline motors fuel atoms can be returned to the tank up to 30 times before being burned. Our engines use the same fuel setup. They are a return-type fuel system. This is done to ensure enough fuel is supplied to the motor. The excess fuel is then returned to the pump or tank. But, if there is insufficient fuel entering the injector, nothing will be returned. So, check the #1 cylinder return line going to the pump. If there is any excess fuel it will show up there. If there is not any fuel being returned, I would start testing your injector pump, or take it to a stanadyne shop for testing.

Hope this helps.

[DmaxMaverick]

It is impossible to have too little fuel, causing smoke, in a Diesel engine. Less fuel only means less power/RPM. White smoke is caused by too little heat to combust the fuel, or combust it completely (the fuel itself will absorb heat, if there is more fuel than heat available). Black smoke is caused by too much fuel for the O2 available, but sufficient heat. Too little heat, causing white smoke, can be caused by a cold engine with poor glow plug operation, retarded timing (fuel is too late, and the heat has already left), or low compression (worn engine, combustion chamber leak, or cranking too slow). The 6.2/6.5 fuel system does not return fuel to the pump, only to the tank. If fuel supply is sufficient to pop the injectors, then the volume and pressure is sufficient. It can, however, be diluted by other properties, like air. Too much air, and the fueling event will be retarded, and may not allow for injector pop at all (the pressure is absorbed by the air bubble, preventing pressure rise to pop the injector). The 6.2/6.5 fuel system has the return system as is for a couple reasons. One is for system component cooling (using the tank and fuel volume as a heat sink), and the other is to manage air infiltration.

[JohnC]

More:

There will always be a little fuel returned from the injectors. This is by design and is how they are lubricated.

Excess fuel provided by the lift pump will be returned directly from the injector pump.

[Kenneth]

Thanks for correcting me. I guess I learn something new everyday, like scrutinize everything you hear/read before you spout if off. I knew our fuel systems were a return-type, but I wasn't sure if they returned fuel to the tank or the pump.

Pressure is a created by restriction/backpressure, right? So, (just a random scenario) what if the pump is pumping the volume too slow because its worn out, and takes longer to build enough pressure for the injectors to pop, causing the injectors to pop later than normal. Could that be a possibilty? Or am I just full of crap again? :) The idea being that the injector pump is worn out and building pressure in the injectors too late, causing improper injector timing. Please correct me if I am wrong. I am just trying to learn here.

[DmaxMaverick]

......Pressure is a created by restriction/backpressure, right? So, (just a random scenario) what if the pump is pumping the volume too slow because its worn out, and takes longer to build enough pressure for the injectors to pop, causing the injectors to pop later than normal. Could that be a possibilty? Or am I just full of crap again? :) The idea being that the injector pump is worn out and building pressure in the injectors too late, causing improper injector timing. Please correct me if I am wrong. I am just trying to learn here.

If this happens, it will be compensated by the governor. To a point it can no longer compensate, and the top end will fall off linear with the shortfall. The pressure stroke where the fuel is actually pressurized is so short, the timing would not be affected at a noticeable amount. Remember, we are talking about fractions of mm3 of fuel at pop pressure per event. If the stroke were unable to develop flow to reach pop pressure quick enough, it won't pop. It will just pass the event and go onto the next (miss). This describes a worn out pump, but the process from running OK to crappy to no-go is usually very quick. Hard warm/hot starts are usually the first indicator.

[Kenneth]

Okay, that makes sense. Yeah, thanks again for correcting me, DmaxMaverick. I realized today when I read it a 3rd time, what I actually said and I feel kind of dumb for saying it. I guess the way you explained how I was wrong made me remember that a diesel literally can run off of any air/fuel ratio and will burn what fuel it has. I guess sometimes with all the engine classes I am taking, I forget some basic theories between gas and diesel.