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LP pump on Yanmar 2GM20F

Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
I can't get any sleep until you solve this thing :snooze: !

With the secondary filter (SF) being empty, sounds like the lift pump is doing a fine job of getting all the fuel it can before it starts sucking air out of the SF.

If you're really serious about solving this then close the fuel supply valve on the top of your fuel tank and then remove the inlet hose to the SF. Take the fuel inlet hose in your mouth and suck for all you're worth:puke:

View attachment 177907

If you're not THAT serious about the problem, then put the vinyl hose from your oil vacuum suction pump (Pela type) into the end of the fuel line which you opened up. Wrap the vacuum tube with tape to ensure you've got an airtight seal.

If you can't maintain a vacuum, you've got an air leak in the fuel line, or primary filter, or fittings, or etc, or etc. Take your pick.

Good luck as always.
Haha...don't think I'll like diesel tasting. Pela type pump will have to do.

Ken Y
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Fitted a spare lift pump last Saturday. Given the tight space it's a two person job. Prime pump to see fuel filling up secondary filter inlet side, then fills the filtered side. Looks good. Tighten all banjos. Ran engine for 10 mins all is good but I should run it longer but didn't have the time. Will run it again this Thursday. Will report back on how it goes.

Ken Y
 
Jan 4, 2006
3,032
Hunter 310 West Vancouver, B.C.
Fitted a spare lift pump last Saturday. Given the tight space it's a two person job.
I'm blown away by the simple fact you were able to fit the spare pump on the engine. :clap: I couldn't even manage it once. Will await your further adventures on this before getting into HOW the secondary filter had been empty of fuel when you previously checked it:

When starved, I unscrew the vent for secondary filter and it was empty on both inlet and outlet.
 
Jun 2, 2011
310
Hunter H33 Port Credit Harbour, ON.
Dismantled my fuel lift pump and I'm disappointed to find nothing wrong :(
Will clean up, assemble, run done test and fit it back next weekend.
What's next to dismantle? Hmmm...., secondary filter.

Ken Y
There are two check valves in the pump housing. If there is damage or debris in the sealing area of one of the valves it will not pump. The check valves are usually not field replaceable but it looks like there is a washer plate holding the valves in place. Maybe you can remove the valves for further analysis. Good luck.
 
Jan 4, 2006
3,032
Hunter 310 West Vancouver, B.C.
The check valves are usually not field replaceable but it looks like there is a washer plate holding the valves in place.
I remember the same problem and for that reason, threw the damn thing as far as I could and went electric.

100_0882.jpg
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
I dismantled the 2 check valves in pump. Disks and springs looks good. Checked the 2 tiny O-rings looks ok too. Assembled the pump and tested by stroking the cam arm, suction and discharge seems ok. Will keep this repaired pump as emergency spare.
Finger crossed for tomorrow longer test run.

Ken Y
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Today warm up engine at neutral for 5 mins, then engage reverse at 1500-2000rpm for another 20 mins. Things look good. Throttle up to 2700rpm in reverse. Was good for 2 mins then rpm starts to creep down to 2500rpm. Bring it down to 2000rpm....holding. Couldn't figure out what's wrong. Will try again next Saturday.

PS: last week was able to race engine in neutral to 4000rpm for a brief moment.

Ken Y
 
May 17, 2004
2,687
Beneteau Oceanis 37 LE Havre de Grace
Today warm up engine at neutral for 5 mins, then engage reverse at 1500-2000rpm for another 20 mins. Things look good. Throttle up to 2700rpm in reverse. Was good for 2 mins then rpm starts to creep down to 2500rpm. Bring it down to 2000rpm....holding. Couldn't figure out what's wrong. Will try again next Saturday.

PS: last week was able to race engine in neutral to 4000rpm for a brief moment.

Ken Y
Is it possible that the throttle slipped from the vibration? I would test max RPM’s in reverse, then let it run around 2700 as you did. If the RPM’s drop again then go to max reverse and see if you can match the original RPMs. If so I would suspect the drop was due to throttle creep.
 
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Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Is it possible that the throttle slipped from the vibration? I would test max RPM’s in reverse, then let it run around 2700 as you did. If the RPM’s drop again then go to max reverse and see if you can match the original RPMs. If so I would suspect the drop was due to throttle creep.
Will give it a try. Thanks for the suggestion.
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Today warm up engine then ran in reverse gear to 2550rpm. Steady no issue for 5-10mins. Throttle up to 3000rpm. After couple mins rpm starts waivering. Push throttle up, rpm goes up then drops. Left at 2500rpm in reverse gear, unable to steady in rpm.
So probably I still have air trap in fuel system or I should put in a brand new fuel lift pump.
Probably try clearing air trap first.
Any thoughts anyone?

Ken Y
 
Nov 21, 2012
130
Yamaha 33 Port Ludlow, WA
What size fuel filter are you running? Everything good there?

Next, I'd check the lines and fittings for debris. If I didn't find anything I'd start replacing the bleed screws, fittings and hoses one by one in that order.
 
Nov 22, 2011
828
Ericson 26-2 San Pedro, CA
Today warm up engine then ran in reverse gear to 2550rpm. Steady no issue for 5-10mins. Throttle up to 3000rpm. After couple mins rpm starts waivering. Push throttle up, rpm goes up then drops. Left at 2500rpm in reverse gear, unable to steady in rpm.
So probably I still have air trap in fuel system or I should put in a brand new fuel lift pump.
Probably try clearing air trap first.
Any thoughts anyone?

Ken Y
Yes, I do have some thoughts--but they are the same thoughts I shared before.

I had the identical problem on my 1GM. It was bedeviled by getting in tiny air leaks. It would run seemingly fine--sometimes for over an hour, sometimes much less. The symptoms were much as you described.

I spent HOURS messing with bleeding and rebleeding, checking connections, redoing connections, running the engine only to have it fail in half an hour, 20 minutes, 45 minutes, etc. etc. I finally said to heck with it! I'm going to start from the tank and just redo the entire fuel delivery system. This took much less time than all of the prior nonsense I (and you) did.

I solved it by ditching the mechanical lift pump (unhooking it, actually). I switched to an electric Facet pump, which I plumbed straight from the output of my 10-micron massive Racor 500 directly to the high pressure injection pump. In doing so I also eliminated the dinky on-engine fuel filter because it was an unnecessary point of failure. (On the 1GM, anyway, the on-engine filters can develop tiny cracks at the bleed screw.) I also replaced all my hoses while I had it all apart (though I don't think the leak was from the hose connections).

The system is now as follows:
Tank --> Racor 500 --> Facet electric pump --> Y-valve --> Output 1: Straight to high pressure pump. Output 2: Taps into injector return line

I also fitted a switch in the engine compartment so I could energize the fuel pump from down there.

This setup is really slick. It allows me to prime both the filter and the engine with ease.

To prime the filter: Switch to Output 2 and energize the pump. It fills the filter while passing the fuel back into the tank. You can tell when the filter is primed by listening to the sound of the pump, which slows down when the filter is full and no longer sucking air.

To prime the engine: Switch to Output 1. Crack the bleed screw on the high pressure pump. Energize the switch. When solid fuel is coming out of the bleed screw, tighten it and then shut off the switch. Done.

There are so many advantages to this system, but I'll not take the time to list all of them. To mention but a few: (1) Removes failure points. (2) Ease of bleeding. (3) Ease of priming filter. (4) Racor 500 is SUPER easy to change, even in a seaway, without spilling fuel. Filter elements are cheap (once you spring for the more expensive Racor 500 itself). Massive capacity. (5) Mechanical lift pump priming lever doesn't work worth a darn. That's now eliminated. (6) Mechanical lift pump diaphragm can fail, putting fuel in your crankcase. That failure mode is now eliminated. (7) Eliminating on-engine filter is one less filter to change.

[Note: There is, of course, no reason that you *have to* go with a large Racor 500. You can keep whatever filter you've got and still do this conversion. But I highly recommend the Racor 500 for our engines for the reasons stated.]

I'll leave it at that.

IMG_20191123_163459292.jpg
 
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Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Fitted brand new Fuel Lift Pump. Changed fuel line from LP pump to secondary filter. Change all copper washers. Hand tested pump to fill & bleed air, fuel shoots out of filter vent like fountain. Good right? Starts engine. Ran beautiful. Rpm up to 3200rpm, stayed a while then rpm starts dropping. Again! Ok, next is to work my way towards the HP Pump.

Ken Y
 
Mar 29, 2017
475
Hunter 30t 9805 littlecreek
Check tank vent and back blow screen on pickup tube at tank before tackling hp pump. Also injectors are popit injectors and usually go bad before pressure pump
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Check tank vent and back blow screen on pickup tube at tank before tackling hp pump. Also injectors are popit injectors and usually go bad before pressure pump
Had cleaned tank, pickup tube, changed Racor filter element, LP pump, hose between LP and sec.filter, changed sec.filter element, bleed air all the way to sec.filter, changed all copper washers that was touched. So next is hose to HP pump, bleed HP pump and.....
Not easy working on engine under Circuit Breaker lockdown. Can't spend much time onboard. It's like "one small step for the engine, one giant leap for my sanity".

PS: had the 2 Injectors serviced at shop, so they're good.

Ken Y
 
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Nov 22, 2011
828
Ericson 26-2 San Pedro, CA
Fitted brand new Fuel Lift Pump. Changed fuel line from LP pump to secondary filter. Change all copper washers. Hand tested pump to fill & bleed air, fuel shoots out of filter vent like fountain. Good right? Starts engine. Ran beautiful. Rpm up to 3200rpm, stayed a while then rpm starts dropping. Again! Ok, next is to work my way towards the HP Pump.

Ken Y
*IF* the on--engine filter is the same or very similar to the one on the 1GM, the housing is prone to develop small cracks at the bleed screw. As I said, I eliminated that issue by removing the on-engine filter altogether.

On the injection pump (again, in so far as it is similar to the 1GM) there is a bleed screw on front that also has a washer that might need changing.

Also, how do you know that you don't have a leak at your Racor filter? Those housings can get hairline cracks so simply changing the filter element wouldn't mean anything. Or at the tank connections? Several places for air to get into the system.
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
*IF* the on--engine filter is the same or very similar to the one on the 1GM, the housing is prone to develop small cracks at the bleed screw. As I said, I eliminated that issue by removing the on-engine filter altogether.

On the injection pump (again, in so far as it is similar to the 1GM) there is a bleed screw on front that also has a washer that might need changing.

Also, how do you know that you don't have a leak at your Racor filter? Those housings can get hairline cracks so simply changing the filter element wouldn't mean anything. Or at the tank connections? Several places for air to get into the system.
Alan, very valid questions you raised. When I finished the checks from sec.filter to HP circuit to Injectors and still no solution, I'll go back to step 1 starting from tank. Wish me luck

Ken Y
 
Nov 22, 2011
828
Ericson 26-2 San Pedro, CA
Alan, very valid questions you raised. When I finished the checks from sec.filter to HP circuit to Injectors and still no solution, I'll go back to step 1 starting from tank. Wish me luck

Ken Y
I do wish you luck! These kinds of issues can be maddening. Let us know how it goes.
 
Oct 29, 2005
2,088
Hunter Marine 326 303 Singapore
Finally!! Problem solved. Start by bleeding air from hp side. Not much bubble. Ran engine at usual test rpm. Starving at 2800rpm. Checked sec.filter, vacuum on hp side and empty on inlet side. Didn't suspect LP Pump 'cos it's brand new. Remove Racor filter assembly and found gunks in filter head at inlet and inside passages. Decide to installed a brand new simpler version of Chinese copy of Racor filter. Fill up with diesel prime LP pump to bleed air bubble and ran test. Initially rpm was unstable. That's to be expected. Shortly rpm stabilise and push it up to 3000 then 3300 and finally 3500rpm. Stayed there very stable
So problem solved. Gunks stuck in inlet passage of Racor filter head assembly.
First 2 photos shows the gunk choked inlet ports. Next 2 photos show cleaned Racor head unit.

Ken Y
 

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