Yanmar 2GM20F fuel question, How much fuel is supposed to come out into the Fuel Return line?

[estopa]

So long story short I was having problems getting fuel pumped out of the fuel injector pump which caused degrading performance and couple times engine cut out. I installed a new fuel injector pump and all looks well. I attached a few videos but what puzzles me is that I would think more fuel would be returning to the tank. I attached a clear tube for testing purposes when I was originally diagnosing my issue. I also attached videos showing the fuel coming out of the fuel lines. Anyone have any experience to how much fuel is supposed to return back to the tank? Seems to only return in dribbles.

Fuel slowing trickling out of return.

Operation of new Fuel Injector Pump

Fuel Delivery to Cylinder #1

Fuel Delivery to Cylinder #2

 

[estopa]

Next step was to replace the fuel lines from Fuel Injector Pump to the Injectors but what I ordered I think were for the non fresh water cooled engines. Will have to follow up tomorrow

 

[Allan12210]

The return is 2-3 times the consumption. If your engine consumes 0.5 gallons/hour at 3000 rpm, then the return would be 1-1.5 gallons/hour. Divide 1.5 by 60 and you get a whopping 0.025 gal/minute (94 ml/minute). Does that seem about what you are seeing?

 

[Benny17441]

When you say "all looks well" does it mean the engine is running fine or still showing symptoms of fuel starvation? The symptoms you express sound to me like a partial blockage in the fuel tank's pick up tube. Had similar symptoms with a jelly like glob of sediments that had formed in the tank. Had the fuel polished and you should have seen the crap that came out of there.

 

[SG]

When you're done with the clear tubing, I'd suggest that you quickly replace it with a rated fuel line!

 

[Charles Erwin]

If the high pressure pump was replaced you should verify fuel pump timing.

Apart from fuel timing the GM series (Bosch type) direct injection sends very little back to the tank.

To the point. What is the problem here and why would return volume be something to consider?

 

[heritage]

Your fuel return amount looks to be about the same as what comes out of my 2gm20f. Not much. I was concerned and did some research. I found that some diesel fuel systems are designed to have a much greater return fuel flow than the gm series yanmars. The large amount and rapid flow of un-injected fuel in the injectors is used to cool the injectors. Apparently this is not necessary in the yanmars.

 

[estopa]

Oh maybe I am making too much of this. I am pretty handy but I don't know much about diesels. This is only the second season with the boat.

It all started early in the season when I went for a day trip 15nm and heard a slightly higher pitch coming from the engine. Sounded like almost a screech for a second or 2 with degraded performance then the motor would hum along. Then mid summer it did it again but motor kept humming along. Then one time after a spirited sail with some waves I got the pickup tube clogged because the motor just died with no fuel going to the motor.

I removed all fuel and removed the screen in the pickup tube. I ran the fuel using the primary racor with a electric pump and saved most of the fuel except for the last gallon. Then I stuck a tube in the pickup tube opening to collect the rest. That fuel got disposed. Then I even put about a half gallon of fuel in and sucked it out. I did this a few times till I was satisfied with the result. I did remove some sludge but not much was in there. Put everything back and changed out all filters and bleed the system.

Then about a month ago I was going out when the motor died again. Luckily I pulled out of my floating dock and had other available docks ahead of me. I was thinking again same issue with fuel. I did notice last time I went out 2 days before the motor barely did 2knots. Anyway with a little more knowledge under my belt I thought again either something in the fuel or maybe air trapped because this motor is a bitch to bleed. When I went to check on the primary filter the racor was leaking out of the bottom with half filled with fuel almost like too much pressure built up because when I opened the housing I experienced pressure like pop. Cleaned everything up and changed out month old filters both primary and secondary and bleed everything. Got the motor running and hobbled back to my dock.

At this time i was at a loss. I basically started at the tank and worked my way up to the secondary filter. Found that many of the banjo bolts either had regular washers or no washers. Put in all new copper crush washers. Primed and Bleed the lines again starting from tank over to primary. Plenty of pressure from the fuel lift pump because when I bleed the secondary and the fuel injector pump there was plenty of fuel coming out with good pressure. But then I started thinking if I am good to the fuel injector pump what gives. Actually at that time after some googling and youtubing I realized what consisted of the high pressure side. I looked at the fuel trying to come out of the fuel injector pump with the fuel lines removed and barely a dribble coming out. AHHA moment, so much pressure on the low side that reflected back to the racor???. Thinking that the injector pump was bad I replaced the injector pump and as you can see in the video it seems like plenty of fuel coming out now.

I was really hoping to replace the fuel lines too from fuel injector pump to the injectors but I made an error ordering from TOAD Marine and received 3GM lines. SO I cleaned up the old lines and installed as you see in the video. I have new ones for the 2GM20F coming soon. SO really just trying to find out if I am in the clear here. As you can see in the videos the fuel coming through the fuel line that would be going to the injector are pulsating out. And when I was bleeding it was spitting out like I thought it should from seeing some youtube videos.

I only had time sunday afternoon after spending Saturday and Sunday to replace the fuel injector pump to take it out in the harbor running at 1500rpm gave me about 2.5knots and 2000rpm like 3.3-3.5knots. This was using my navionics on my phone. Seems like its responsive and didn't cut out on me. I will have to take it out this week and go for a nice motor run. Oh and I did bleed under load too as I found out with these motor after more googling.

Really the only question or reluctance to call success is that I didn't see a whole lot of fuel coming out of the return. Again I used the clear tube to just see results. Of course the original return tube was reinstalled to the tank. But since some of you guys stated not a whole lot goes back to the tank I think I can sleep better at night. In the off season I plan on pulling the injectors and getting them serviced too. I talked to the previous owner and he only replaced the lift pump when he first got it 10yrs ago and nothing else to the fuel system.

I plan to take it out sometime this week then maybe a long motorsail this weekend. Documenting various speeds and rpms.

Thanks folks for all the insight to date.

 

[Benny17441]

You did a good job but make sure not to forget to replace the fuel cap gasket. You do not want rain water in the tank. Also make sure the tank's vent is not plugged as sometimes critters nest there. If the engine runs good I would not worry about the return volume.

 

[estopa]

Thanks Benny good point. I will look at those gaskets. The vent seems fine I took a look at it a few months back when initial issue with the pickup tube.

Well yesterday I went out for a few hours in varying rpms and all seems well. I think I should be in the clear at this point.