518 fuel pump problems

[Spartan]

Soooo...  It's hard to find info online about older cat equipment it seems like so I will give it a shot here.

Fuel pump is starving the engine during cold temps.  gets air in it and stalls out the engine, have to bleed the pump everytime it dies.  Can't tell if there is a air leak into the line/pump, or if there simply is not enough fuel flow to the pump.   Runs fine in warmer weather.

Here is what we have done so far.  Fuel lines looked cracked and worn, replaced from tank to filter housing with new.  Replaced filter.  ran good one day but then temps fell even lower and would not run the next.  Fuel is not gelled fwiw.  Primer pump was taken off to inspect to see if there was a leak there.  when reinstalled, would not pump the fuel pump up.  and after priming it for some time, the fuel filter would be drained down to about half.  The primer was old,  and leaked a lot of fuel out while pumping so we replaced that as well.  still would not pump up, still drained the filter (seemed like it was just drawing from the filter and not the tank). Made sure there was no junk in the filter housing ports.   blew fuel line out from filter to tank with air, would pump up then.  finally started it up, and it starved out again.  Thought it might be junk in the tank, pressurized the tank from the cap area, and fuel seemed to flow out the line very well.
At a loss as of now....   I have heard there are screens that can get plugged but can't find where they would be in the pump.  It's a 3304 motor.
The pump is not the original pump, I think the machine is a 78.  The pump I think is newer.

Could the pump just be worn?  If so, we though about installing a in-line electric pump to supplement it for the mean time in the cold, don't know if that would help..

Any Ideas guys?

[giant splinter]

Check the return side of the pump to see that fuel is getting back to the tank through the return line. you should be able to loosen the fitting where the metal line changes over to the tank return line .... just look to see if the fuel is completing the circuit, on some of the fuel systems its possible to see the fuel return line dribbling fuel back into the fuel tank from the top ..... adding a small bendix electric fuel lift pump might help but going through and purging everything will be the best way. Sometime all it takes is just the smallest air leak to foul up the fuel delivery system, it never hurts to go back through and double check to see if everything is tight and no signs of leaking in the areas around any of the lines and fittings.

[Spartan]

Well, there is no return line that I know of..  have not been able to find one and definitely none going back to the tank.

[JustinW_NZ]

I've just been though a similar exercise with my little treefarmer

Now has external electric pump and new filter and housing and mostly new fuel line.
It took me ages to bleed all the air out and get it running for more than the fuel in the filter it was draining.

I rechecked and retightened all fittings as well, so either persistence or a retighten worked I think ???

Cheers
Justin

[coxy]

I have the same thing happen every time I put new filters on it will suck air some place for a few days then stop ??? ??? have never found out why  new lines fittings you name it   do you have the glass filter down by your right foot  mine was sucking air there and I bypassed that filer and i added  another spin on filter I haven't changed the filters in 5m so its been working good   ;D next week it will run like crap for a few days after changing them               good luck with it

[Spartan]

thanks guys.  It's down to one filter now, used to have 2 but it was bypassed and removed long ago.  -17 on the mountain this morning, so I don't know if we will make the trip today.   will recheck fittings.

[deastman]

There should be a small screen in the line just before the fuel goes into the transfer pump. It looks like a  hex nut about 1 1/2" long. Usually the fuel line hooks to a 90* elbow that screws into the screen housing. Use a 3/4 wrench to remove the screen housing and elbow from the inlet of the pump and then remove the elbow and it takes an allen wrench to get the screen out. The screen is only about 1/4" to 3/8" in diameter.

[Spartan]

I will look for that screen, although, on this pump the line goes into the filter housing and then there is a metering block that it goes into from there that I think goes into the transfer pump, not sure though.

[Spartan]

put an electric in-line pump in and that solved it for now.  Runs fine in the cold.  Must be a worn fuel pump.

[logloper]

Find your lift pump. It has a manual plunger on top. There is a sediment bowl underneath the manual pump. Unscrew and clean. it has a screen inside that plugs with rust or other junk

[Spartan]

I did look for something like that but there is nothing underneath the manual pump to unscrew and take apart.  It bolts to the lower part of the main housing in the front part of the pump and there is nothing around it to unbolt unless you want to take the main pump apart.  Dunno

[logloper]

Been a year or two since I worked on one, and don't have my books here. Seems like the bowl under the manual pump has a nut molded into the bottom, not really anything to unbolt. Just unscrew the bowl itself?

[loggah]

If you have the glass stanodyne filter, in cold weather lots of times the air will get pulled into the filter around the rubber o-ring! when its warm there fine,when its cold they leak air.You can try and bend the spring latch to put more pressure on the filter or make a thin shim,even a piece of cardboard from the filter box ,put it between the clip and the filter this usually works. Don

[David-L]

As Loggah says if glass filter those o-rings can not work so well in cold. you might  see air bubbles in the top of the filter as I did on a few of my JD 55 series tractors. New filter and shim under the filter clip and problem solved. thats if you have glass filters though. if not air in system or worn pump. Good luck.

[Spartan]

I may have to take a picture of the pump for you guys cause we don't have any of the above mentioned items.  No glass filter for sure, just 1 screw in canister.