MEP-701A Fuel Pump Priming Question

[UMR_Engnr]

I recently bought a MEP-701A with the ONAN diesel engine. I have been trying to prime it but it doesn't want to. It didn't feel like there was any resistance on the prime lever, so I removed the fuel pump. That is when I discovered the transfer rod was all the way in the up position. So I reconnected the fuel pump and ran the starter. After that, there was resistance on the prime lever so I pumped it for quite a while but there didn't seem to be any progress. There was no fuel in the fuel filter. I removed the fuel pump again and placed the inlet in a container with diesel fuel and left the outlet open to the air. If I actuated the prime lever it would suck up fuel but then releasing it would cause the fuel to go back into the container instead of expelling air out the outlet. I opened up fuel pump and there are some one way valves but then there is also a little hole that appears to connect the inlet and outlet that allows air to flow back through the inlet.

So my question is what am I missing? Is my fuel pump behaving appropriately? Is there a check valve somewhere in the system that is stuck? Is there more to this process that I'm overlooking?

Any help is appreciated. I really want to get this thing up and running. Thanks

 

[UMR_Engnr]

Here is a picture of the hole (circled in red) that is letting air get back into the feed instead of forcing it out the return line. Anyone have any ideas? Thanks.

 

[ETN550]

I've never had one apart. (And I've got about 35 of these running in the last 2-1/2 years) They do leak backwards over time and loose prime. Some in a few hours others take weeks. With the cam lobe off the plunger it takes 250 - 400+ quick strokes of the lever to fill a dry filter and get air out the top thumbscrew bleed. One thing I don't like is that they handle unfiltered fuel so the check valves can get hung up with dirt.

I may prime them 100x in the course of 20 sec or so to get it flowing prior to a start after sitting. If it is quiet you can hear the fuel returning to the tank if the filler cap is off.

 

[ETN550]

I'm sure the hole has a purpose.

To fill the system, I put my finger over the return in the tank and use a mighty vac on the bleed screw on the filter cover to draw fuel into the filter housing. Then it's only a few primer pumps to complete the process.

Your pump might be air locked. If it has solid fuel in it it should move fuel and shove the air down the line. The air will bypass the injection pump.

 

[UMR_Engnr]

Thanks for the response ETN550. Isn't pulling a vacuum from the bleed screw to fill the filter housing similar to just pouring fuel into the housing which the manual warns against for fear of damaging the injection pump? Can you tell me where the check valve is on this system?

 

[ETN550]

Thanks for the response ETN550. Isn't pulling a vacuum from the bleed screw to fill the filter housing similar to just pouring fuel into the housing which the manual warns against for fear of damaging the injection pump? Can you tell me where the check valve is on this system?

The check valves have to be in the pump as they are not elsewhere. Not sure what they look like as I never had a pump apart. There are repair kits on the big auction site maybe they have pictures of the parts.

Although often practiced, it is not advised to pour fuel into a filter housing due to the risk of getting dirty fuel into the clean side of the filter or fuel system. The vacuum method is not the same as pouring in fuel. Using a vacuum to draw fuel from the tank through the fuel pickup and lines into the housing with an installed filter and sealed lid will not allow dirty fuel to get to the clean side of the filter. Using the priming pump to fill the filter housing accomplishes the same and avoids getting dirty fuel on the clean side of the system. However, hand priming often takes over 400 strokes of the pump to fill the housing.

 

[UMR_Engnr]

Sounds good. I truly appreciate the feedback. I didnt' realize the concern was dirty fuel getting to the pump, but that makes sense. I'll put the pump back together and try the vacuum method.

 

[ETN550]

Please report results. Thanks,

 

[UMR_Engnr]

Thanks to ETN550s trick of using a hand vacuum to fill the fuel filter, I was able to get the system primed. However, once pressure built in the fuel filter the feed hose to the injection pump started spraying diesel. It looks like the hose cracked right at the bend from the fuel filter under some of the metal guard. Anyone have suggestions for replacing this hose?

 

[ETN550]

Thanks to ETN550s trick of using a hand vacuum to fill the fuel filter, I was able to get the system primed. However, once pressure built in the fuel filter the feed hose to the injection pump started spraying diesel. It looks like the hose cracked right at the bend from the fuel filter under some of the metal guard. Anyone have suggestions for replacing this hose?

The hose ends should be 37 degree JIC -4 size. Any hose shop should be able to build a hose. Bring in the old one for them to copy.

You might try using the hose from the aux pump to the top of the tank if you want to get it running. It's probably way too long but it should work as temporary. I built a skid base for an old Onan gen and used the parker push lock hose with 37 deg JIC ends. That hose is softer and takes bends much better. It's fuel rated and the push lock ends work great. been using it for over a year now.

 

[UMR_Engnr]

I went to the local speedshop today and found some parker 836 push loc hose in their assorted hose bin. Cut the old hose off, pushed the new hose on, reinstalled and no more leaks. I reprimed the system but didn't get a chance to start it because the kids are sleeping. Hopefully tomorrow it starts up and the issues are behind me.

 

[UMR_Engnr]

I powered it up over lunch today, and it started up fine. No leaks. It ran a little rough while warming up but smoothed out. I adjusted the throttle and measured ~112V @ 60Hz through the convenience ports. I haven't put a load on it. Man it is loud with the ASK panels off. I hope the ASK panels work well to quiet it down, because it is currently in my opinion too loud to run in a residential setting full time.

 

[steelypip]

They're pretty bearable with the ASK installed, but watch for rattling panels. The exhaust comes out low on the side, and you'd probably manage a lot of noise just by pointing it up with an elbow and extension. Cooling air exhaust is also up, which helps. Definitely not as quiet as an MEP-802A, though.