yanmar 2GMF air in fuel problem [again!]

[vas]

evening all,

my generator 2GMF continues to give me starting problems even after the full rebuilt.
fuel layout is:
tank level currently slightly lower than engine LP and HP pumps
3m new hose to LP pump
New 400mm hose with banjo to compression fitting (or however you call them with the conical face, no washers, or anything needed to seal)
CAV296 filter
New 40mm hose as before the filter to HP pump.
CAV has replaced the original yanmar filter as the bleed screw threads were stripped and wasn't generally happy with it, feeling it was leaking (had the same issues)

Now we have the following:
works fine as long as you bleed it at the HP pump inlet (release the banjo, 3-4 turns of the starter, then fires)
works as long as you want no problems, never dies.
leave it for an hour or two, fires up on first push of the button, fine.
Leave it for 5-6h (or overnight) simply wont start unless you bleed again.
Have tried all sorts of things, failed miserably.

So, today went a step further:

replaced all copper washers on banjos and connectors with these metal/rubber combo things (sorry forget the name) all brand new.
replaced the second inlet of the CAV filter with a pickup for a carburetor style pressure/vac gauge.

Bled the thing again, fired straight up, gauge showed 3.5psi whilst running at 3K rpm (old school 2pole generator) going up to 4.2psi when I turn off the engine.
Checked three hours later before leaving the boat in the evening, pressure was down to 1.5psi, engine fired up straight away (temps were down to 30C) pressure again up to 3.5psi.
Left it, will go back in the morning, I bet it wont fire up again and the gauge will show 0 if not - ...

Considering I cannot spot any diesel leak (and I've spent a fair amount of time searching!) I feel the only two candidates are the bloody filter (I really hate it!) or the LP pump.
I've taken apart both of them, reassembled, nothing odd in either.

I've also bought a 1/2 USwhatever thread stop cock so I can add it either between LP and CAV or CAV and HP pump.
I'll try fitting it between LP and CAV tomorrow and see what's going to happen.
Am I right in assuming that if pressure doesn't drop I better replace the LP pump as the non return valves are leaking fuel back towards the tank?
Oil level is steady and doesn't change, so cannot believe the membrane leaks down to the sump.

Before forking out the 60-70quid of the LP pump, is there an easy way to test the non return valves in this thing?
Have compressed air onboard, was thinking if I could carefully pump backwards from LP outlet some air and see what happens
When I opened it up, membrane looked good, little crude in there (v.little tbh) and used new gasket sealant before putting it back together.
from what I can remember, the non return valves where nice and clean.
Further I cannot trace and diesel around it or on either banjo...

ideas welcomed

V.

 

[bristoljim]

evening all,

my generator 2GMF continues to give me starting problems even after the full rebuilt.
fuel layout is:
tank level currently slightly lower than engine LP and HP pumps
3m new hose to LP pump
New 400mm hose with banjo to compression fitting (or however you call them with the conical face, no washers, or anything needed to seal)
CAV296 filter
New 40mm hose as before the filter to HP pump.
CAV has replaced the original yanmar filter as the bleed screw threads were stripped and wasn't generally happy with it, feeling it was leaking (had the same issues)

Now we have the following:
works fine as long as you bleed it at the HP pump inlet (release the banjo, 3-4 turns of the starter, then fires)
works as long as you want no problems, never dies.
leave it for an hour or two, fires up on first push of the button, fine.
Leave it for 5-6h (or overnight) simply wont start unless you bleed again.
Have tried all sorts of things, failed miserably.

So, today went a step further:

replaced all copper washers on banjos and connectors with these metal/rubber combo things (sorry forget the name) all brand new.
replaced the second inlet of the CAV filter with a pickup for a carburetor style pressure/vac gauge.

Bled the thing again, fired straight up, gauge showed 3.5psi whilst running at 3K rpm (old school 2pole generator) going up to 4.2psi when I turn off the engine.
Checked three hours later before leaving the boat in the evening, pressure was down to 1.5psi, engine fired up straight away (temps were down to 30C) pressure again up to 3.5psi.
Left it, will go back in the morning, I bet it wont fire up again and the gauge will show 0 if not - ...

Considering I cannot spot any diesel leak (and I've spent a fair amount of time searching!) I feel the only two candidates are the bloody filter (I really hate it!) or the LP pump.
I've taken apart both of them, reassembled, nothing odd in either.

I've also bought a 1/2 USwhatever thread stop cock so I can add it either between LP and CAV or CAV and HP pump.
I'll try fitting it between LP and CAV tomorrow and see what's going to happen.
Am I right in assuming that if pressure doesn't drop I better replace the LP pump as the non return valves are leaking fuel back towards the tank?
Oil level is steady and doesn't change, so cannot believe the membrane leaks down to the sump.

Before forking out the 60-70quid of the LP pump, is there an easy way to test the non return valves in this thing?
Have compressed air onboard, was thinking if I could carefully pump backwards from LP outlet some air and see what happens
When I opened it up, membrane looked good, little crude in there (v.little tbh) and used new gasket sealant before putting it back together.
from what I can remember, the non return valves where nice and clean.
Further I cannot trace and diesel around it or on either banjo...

ideas welcomed

V.

A little air must be getting in somewhere letting the fuel drop back - if it does not fire at all it would indicate air getting in low down on the injector pump as there is enough fuel in the pipe down from the filter to give a short burst before the air gets to the element which stops it.You could prove this theory by opening the bleed bolt on the filter,leave it overnight & start without bleeding,tighten the bleed bolt & see if you get a short run with fuel in the pipe
Jim

 

[vas]

thanks, interesting approach, will have to try it as well.

Anyway, an update: as expected, the next morning it wouldn't fire, so fitted the stop cock between the LP and the CAV last night, bled, run the engine, stopped the engine, closed the stop cock.
Pressure registered again 4.2psi
This morning pressure was still 4.2psi, but on opening the stop cock dropped significantly (but not down to 0psi). Engine wouldn't fire, bled fired up again...
The fact it didn't drop to zero is slightly worrying implying there's a leak either side of the stop cock!

However, playing around yesterday I noticed that the banjo from LP to filter has a 10mm hole, where as the bolt is 8mm a fair amount of play when fitting and securing it. Couldn't get one made properly, will do tomorrow morning and hope it improves the situation.
May also have a go at returning to the original filter and ditching the CAV.

Generally, LP pump is 8mm banjos and HP is larger than 10, guess 12, will measure accurately.

will report again tomorrow or the day after with my findings.

cheers

V.

 

[vas]

another update, not getting much wiser, just narrowing my options...

New hose 8mm banjo (LP out) to CAV in. Bled, worked fine, left it 6h came back an hour ago, wouldn't fire. BTW, removed the gauge as I was worried that maybe this/or it's hose was also leaking.
BTW, for the record CAV296 between LP and HP pumps, has two inlets, two outlets:
gauge on second INLET of the filter shows 4-5psi with engine running
gauge on the second OUTLET of the filter shows 8psi with engine running
isn't that a bit odd?

Back to square zero, so bypassed the CAV filter altogether, go from LP to HP no filter whatsoever it the circuit-obviously that's only for testing, will refit something that doesn't leak (if that proves to be the culprit)
Bled at the HP in (which is 12mm banjo btw), run it for a while, all fine.
IF it works on first crank tomorrow, means that the CAV was leaking and goes to the skip.
IF it does the same, the CAV comes back in and I'll remove the LP pump and plumb it to a rubber impeller oil transfer pump I have knocking around and try sucking out of the LP inlet and see. I could also blow in, block the outlet and dip it in a water bowl and check for bubbles, but I guess that's not going to be extremely smart, so I'll pass for now

fwiw, here's a pic of the LP pump when I opened it up in Dec, to check/clean/reseal:
non return valves looked good (to my eyes at least) and clean. They are tiny anyway, not much you can do with them I guess....

V.

 

[vas]

note, the engine was repainted as part of the rebuilt, and it's obvious that there was some leak on the top of the membrane as you see it in the pic above as paint had "leaked" in. Cleaned carefully all surfaces, and added a thin strip of instant gasket to make sure I get a perfect seal. Now sure how I could do that without instant gasket tbh

V.

 

[bristoljim]

note, the engine was repainted as part of the rebuilt, and it's obvious that there was some leak on the top of the membrane as you see it in the pic above as paint had "leaked" in. Cleaned carefully all surfaces, and added a thin strip of instant gasket to make sure I get a perfect seal. Now sure how I could do that without instant gasket tbh

V.

Had a problem with a CAV filter on a new installation once ,removed it pressure tested with air & found leak on one of the blanking plugs,I think the copper washer was hard
Jim

 

[vas]

Had a problem with a CAV filter on a new installation once ,removed it pressure tested with air & found leak on one of the blanking plugs,I think the copper washer was hard
Jim

replaced them all with these metal/rubber washers.
However, I think the bleeding screw is suspect to leaking in mine. For good measure I put a new copper washer and a small o-ring together there
I'll know for sure in the morning!

V.

 

[rgarside]

If you have copper washers in the system have you annealed them? Once you clamp up on them they work-harden, so if reused should be re-annealed to make them soft again.

 

[vas]

If you have copper washers in the system have you annealed them? Once you clamp up on them they work-harden, so if reused should be re-annealed to make them soft again.

have replaced everything on the whole diesel system with dowty washers (found the name, you know the metal/rubber combo ones). Going there in a while, will report my findings.
Mind haven't done anything on the HP to injectors part of the system but that bit seems to be fine as IF I bleed immediately at the HP in, engine fires up straight away.

V.

 

[rgarside]

I saw you mentioned one on a bleed screw.
D

 

[vas]

True, but I already bypassed the whole filter...

Anyway testing on board, ended up unbolting the lp pump and plumbing the pressure gauge straight on the lp outlet. Same thing, pressure slowly dropping.
Pumped again, removed the inlet from tank, let it rest with the inlet hole facing upwards, and watched over a period of two mins the pressure dropping on the gauge and the level rising in the hole eventually flooding out.
So, for sure it's the lp pump
Opened it up again, noticed one of the valves was slightly prodruding having bent the retaining metal plate. Everything is clean, membrane must be intact as I cleaned the engine side as much as I could and didn't spot any diesel coming in...
Anyway will have another go if that fails I ll order a new one.
Puzzled how these tiny valves seal though! Fibre disk pressed with a tiny spring onto a bronze base, seemed made for leaking back.
Also wonder how diesel is leaving this whole assembly, unless air can enter somewhere up line. So for sure a combination of issues, hence eventually starting without bleeding this morning but after a few longish 15sec sessions...

V.

 

[vas]

stretched the tiny springs in each non return valve, cleaned (tbh they were really nice and clean...) all bits, turned the fibre disk the other way round, reassembled and tested the same way.
After an hour there was a wee bit of diesel at the bottom of the M12 hole where the banjo bolt goes and a small drop in pressure on the gauge.
I assume that's acceptable-anyway cannot think of a way to improve it with this Mikuni pump.
Anyway, reassembled the lot (again without any filter) bled (felt that the LP was pushing more fluid, could be due to the hours spent down there though...) fired up first go.
Left it at 5pm I may go at 11 and have a go at starting the generator. If it fires straight away, I consider that fixed and will refit a filter. If not I'll order a new LP pump.

V.

 

[vas]

me again

just a thought, since I established that the membrane of the LP pump is OK, ie not leaking in the sump and the thing is pumping (after the reassembly I measured up to 8psi) if there's a leak back to the supply pipe, couldn't I simply fit a non return diesel compatible valve just before the LP pump? Definitely cheaper than the 60quid for the LP pump!

Is that acceptable?

V.

 

[bristoljim]

me again

just a thought, since I established that the membrane of the LP pump is OK, ie not leaking in the sump and the thing is pumping (after the reassembly I measured up to 8psi) if there's a leak back to the supply pipe, couldn't I simply fit a non return diesel compatible valve just before the LP pump? Definitely cheaper than the 60quid for the LP pump!

Is that acceptable?

V.

Yes should be ok
Jim

 

[vas]

closing the thread as following fitting a non return valve a foot before the lp pump, yanmar starts on the first 3sec on the starter even when left for a day or two!

So if you have:
air in circuit,
no visible leaks,
diesel tank lower than engine,
oil level in engine NOT rising,
a n/r valve is a cheap solution compared to replacing the low pressure pump which is most likely "loosing" diesel back in the line due to weakened valves within the lp pump. Wont harm anything, and I doubt there's a cheaper test to see what else maybe wrong with the engine!
Mind depending on what n/r valve you get, you may have to "regulate" it so that it doesn't need a bar pressure to open (when I bought mine I couldn't blow through it in the right direction!)

cheers

V.

 

[vas]

updating a closed thread

during the summer, yanmar started the same tricks, actually didn't work properly for that long.
So, last month following a partial dismantle of the engine front "lid" to sort out a small oil leak and another HP pump related mistake of mine, I had a blanking plate for the LP hole made and fitted, and bought a 60euro pulsating petrol/diesel automotive el. pump. A no-name CN thing that lets fuel through effortlessly when not connected.
I also scrapped the non-return valve. So system now is:

stopcock at day tank,
3m hose to engine mounted el.pump
short hose with banjo to yanmar stock filter
banjoed hose from filter to HP pump

Amazingly it works (now for over a week...)
Even more interesting is that engine runs without powering the el.pump, so I wired the el.pump to the starter, so only runs for the time engine is cranking. Engine runs at 3k rpm smoothly no issues.

If lockdown keeps till easter down here (which I'm v.much afraid of!) I'll take apart the yanmar filter housing and fit a vacuum sender on top so I can monitor vacuum values throughout operation and shutdown periods.

So, if any yanmar GM owner is facing similar problems, a new LP pump maybe in order!

cheers

V.

 

[jim.howes]

another update, not getting much wiser, just narrowing my options...

New hose 8mm banjo (LP out) to CAV in. Bled, worked fine, left it 6h came back an hour ago, wouldn't fire. BTW, removed the gauge as I was worried that maybe this/or it's hose was also leaking.
BTW, for the record CAV296 between LP and HP pumps, has two inlets, two outlets:
gauge on second INLET of the filter shows 4-5psi with engine running
gauge on the second OUTLET of the filter shows 8psi with engine running
isn't that a bit odd?

Back to square zero, so bypassed the CAV filter altogether, go from LP to HP no filter whatsoever it the circuit-obviously that's only for testing, will refit something that doesn't leak (if that proves to be the culprit)
Bled at the HP in (which is 12mm banjo btw), run it for a while, all fine.
IF it works on first crank tomorrow, means that the CAV was leaking and goes to the skip.
IF it does the same, the CAV comes back in and I'll remove the LP pump and plumb it to a rubber impeller oil transfer pump I have knocking around and try sucking out of the LP inlet and see. I could also blow in, block the outlet and dip it in a water bowl and check for bubbles, but I guess that's not going to be extremely smart, so I'll pass for now

fwiw, here's a pic of the LP pump when I opened it up in Dec, to check/clean/reseal:
non return valves looked good (to my eyes at least) and clean. They are tiny anyway, not much you can do with them I guess....

V.

Hi why so many copper washers on the one banjo bolt, is the banjo too long and bottoms out?

 

[vas]

no, just temp storing all my copper washers in one place, avoid loosing them
Only one copper washer on each side of the banjo thingie, but now all replaced with dowty washers.

cheers

V.

 

[jim.howes]

Brilliant, I will now get rid of my welding rod S hook.?

 

[vas]

If lockdown keeps till easter down here (which I'm v.much afraid of!) I'll take apart the yanmar filter housing and fit a vacuum sender on top so I can monitor vacuum values throughout operation and shutdown periods.

So, if any yanmar GM owner is facing similar problems, a new LP pump maybe in order!

cheers

V.

me again,
well still in lockdown and last week I fitted a -15psi to 30psi analogue pressure sensor on the top of the stock yanmar filter (used the one of the bleed screws), hooked it up on my arduinos and got fuel pressure data on my N2K bus and subsequently on the grafana visualiser from where we get this:



Now top graph has oil, seawater (and as of this evening) fuel pressure.
Lower is coolant and EGT temps (ignore the 300C peak of coolant, was editing s/w and messed up a bit) The two yellowy peaks for circa 35C on EGT is when engine fired up twice for a couple of mins each time.

Note that fuel pressure starts at 2bar (cranking and el.fuel pump working), drops to around 1bar in operation.
Before 19, engine was off and within an hour dropped form 0.9bar to 0.5bar. At which point I started again the engine for a couple of mins (fired up straight away) pressure went a bit higher and within almost 2h with engine off, pressure zeroed.
This matches (more or less) my experience of ease of starting after leaving for different periods of time.

If I try to start it tomorrow it will take 3 -4 crank sessions of 10secs each before it fires up. It will fire up eventually (that's progress wont need to open hatch, go down to e/r and bleed it!) but not satisfactory imho.
Last thing I'll do tomorrow is fit a non-return valve just before the el.pump (although I'd expect it features a non-return valve and it's brand new) and watch the pressure drop.
I'm worried that engine will have problems running as I only run the el. lift pump whilst cranking (could change that of course with an extra relay)
Other than that I'm running out of ideas:
Stupid stock yanmar filter is nice and clean, tested MANY times with nice soft toilet paper folded to spot any point of leak (used to have some last season, replaced seals) nothing, all clean!
h/p pump also clean.
Level of diesel on tanks is say 100mm lower than the el. lift pump and say 300mm lower than the engine mounted filter.

ideas where else to look? More drastic step would be to replace all hoses to tanks (3-4yrs old look clean!) or get a 20lt jerry can with diesel next to the geny are reduce hoses to 300mm.

cheers

V.