Komatsu pc300-lc-5 losing fuel prime

[Junk runner]

My 300 Komatsu is losing fuel prime when it sits. Is there a check ball in the fuel line that could be bad? Or? Thanks

 

[heymccall]

The overflow valve is suspect. It IS the banjo bolt in the circled area. It purpose is to maintain 15psi in the fuel supply system. Any extra pressure opens the valve and returns it to the tank. They do wear out. When worn, hard starting and/or low power are the symptoms.

 

[heymccall]

This video shows its internals. Short of finding debris in there, the valve is replaced as a whole.
While your machine has a SAA6D114 Komatsu engine, the pump is still a Bosch P7100, just like on a Cummins 5.9.
Or, at least, that's what was in my PC300LC5.

 

[Junk runner]

That’s for the great info I will check that out this afternoon

 

[John C.]

If it is a Dash 5 Komatsu, the engine is a S6D95. The banjo bolt on the bottom of the hand priming pump has a screen in the center of the bolt that will be completely plugged. The screen will be made of either brass or plastic depending on the age of the machine. It unscrews from the end of the bolt and you can blow it out with air pressure. Below is a link to a video showing all the maintenance stuff on any Dash 5 Komatsu excavator. The machines in the video are smaller but the practices shown are the same for all that manufacturer's excavators.

 

[John C.]

I made a mistake on the engine model. It should be a S6D108.

 

[heymccall]

My bad on the engine model. I still believe it has a P7100 pump, though.

 

[thepumpguysc]

Weather it’s a Bosch in-line or a Zexel in-line, they both have an overflow valve on the fuel outlet.
The big difference is the Zexel pump will have that filter screen in the banjo bolt for the fuel inlet on the supply pump..(the hose below the hand primer)
Good luck.

 

[Junk runner]

Here is a pic of the side of my pump. Just to make sure I have this correct. The screen is on the fuel feed line on the right side of the primer pump? The check ball and spring are in the banjo bolt on the left side of the injection pump? Thanks for the videos great information.

 

[Junk runner]

 

[John C.]

The fuel screen is in the banjo bolt under the hand pump. The check ball for the return is under the bolt with the dark rubber hose dropping down. It looks like a bolt going into the back of another bolt.

 

[Junk runner]

Ok I’ll check those out and see what happens. Also one of my tracks runs a little slower than the other. There’s no hesitation when you push forward or backwards it’s just slower. Is there an adjustment for that or more likely a bigger issue.

 

[John C.]

There is but it takes at least four gauges read at the same time. I’ll post a video of the tune up tomorrow or you can search for it on YouTube.

 

[Junk runner]

I tried to find the video but no luck so far so if you could post it or tell me what to look under it would be greatly appreciated

 

[John C.]

Below is the link. Sorry it took so long. Just got back home.

 

[Junk runner]

Thanks for all of your guys help. I ordered some parts and will see what happens

 

[ktm250rider]

Check all your hoses. I went through stalling issues on my Hyundai. Replaced the lift pump and that worked a little, then started replacing fuel line hoses. Each time it would help but would eventually stall. The hoses had very slight cracks at the fittings. They wouldnt leak so that you would see fuel, but just enough to loose prime over time.