Yanmar 3GM30F Baffling Diesel Problem - Chapter 3.

[BobnLesley]

Good evening Gentlemen, we're now into week three of our fuel problems and becoming increasingly baffled not to mention disheartened; I even turned to the local diesel mechanic - highly recommended by some, but then again, seemingly the only one here in Shelter Bay, Panama - to let him have a try, sadly he managed no better than we had ourselves and the run-time record remains at 2 hours and 50 minutes!

The original 'problem' was water, crap, diesel-bug in the tank, but we are 99% sure that is all now clean and the tank contains only good/fresh diesel. We have stripped out and pressurised the whole fuel system (bottom of the tank's pick-up pipe to the mechanical fuel lift pump union) with diesel, found no leaks whatsoever and reassembled the system. We have temporarily replaced the mechanical lift pump with both another similar (and known to be working) mechanical lift pump and at another time with an electrical in-line pump; we've also replaced both primary and secondary filters about six times now.

The outcome remains the same: After air-bleeding the system, we can start the engine - it spins/starts in 2-3 seconds just as it always has - whereafter it runs smoothly and sweetly for somewhere between 15 minutes and two hours, then the revs drop, the engine coughs/splutters (classic fuel starvation noises?) and then stops.

Today's experiment addressed our 1% doubt over the fuel/tank and saw us drawing and returning fuel from/to a clean jerry jug - filled with fresh, new & filtered diesel - sat atop the permanent fuel tank, pulled via the mechanical pump to the secondary/fine filter and on into the engine. It ran sweetly for just over two hours, then stopped as usual; tomorrow I'll repeat the experiment but with the jerry-can located at/above the level of the fuel pump, thereby gravity feeding it.

Any suggestions as to where else to look/try - I might've tried them already, but throw them all at me. I'm not getting any clouds of white or black (water/diesel) exhaust smoke, it's 'as usual' just a light grey and given the engine's circa 3500-4000 hours, there's very little even of that. I cannot percieve how any fuel/air/filter/lift-pump problem could allow the engine to start easily and run for an extended and varied time period before causing a stoppage; what about the injection pump? I've never had a problem with one of those, but had understood that either they worked or you didn't even get the engine to fire-up?

 

[bigwow]

I had a similar problem on one of my Volvo 2002's turned out to be a build up of some almost cement type crud in the head of the filter. After changing numerous filters I took the whole assembly off, in desperation, and there it was.

 

[duncan99210]

Bigwow may have something there. Little bit of crud which doesn't block things, then it shifts a bit and blocks things. Other thought is are the filters actually catching anything? If they're not getting bunged up with crud then crud getting sucked into the system isn't the problem and your tank cleaning has worked.

 

[Spyro]

The fact it starts again easily after bleeding points to an air leak in the fuel system. Air can be drawn in but won't necessarily show up as a diesel leak. You may need to redo all fuel line joints and try again.

 

[PetiteFleur]

This is exactly what I had soon after I fitted a new engine, fuel tank and fuel lines. Ran perfectly for 50hrs then just stopped. I also changed filters etc etc. In desperation I rang the local Beta engineer in Ipswich(I was in Holland at the time). He immediately said - 'air leak, just go round and tighten all unions' - which I did and it's run perfectly ever since. Never did find out which union was causing the air leak.

 

[C08]

I had a 15HP Yanmar that exhibited the same symptoms i.e. would run ok for an hour or two and then splutter and die. It drove me crazy and I went through all the usual things, fuel, filter, lift pump, injector pump, governor springs etc. What it turned out to be was that this engine had the surplus fuel from the injectors run back into the top of the filter bowl before the injectors. Somehow this was getting aeriated and the air in the injectors stopped the engine until then having been bled was ok for a while. Piping the surplus fuel direct back to the tank where presumably bubbles could disperse thenmselves solved the problem commpletely.
I am not suggesting that you have exactly the same problem but this may stimulate some other ideas?

 

[Cheesey69]

It's also possible for the injector pump to fall internally and draw in a tiny amount of air that eventually adds to a large amount of air.
This happened way back in the day to a jcb engine we was working on and the only tell tale was a tiny amount of diesel around the injector pump shaft.
Trouble is that we just swapped out parts until the thing was reliable again.

 

[lpdsn]

What's the vacuum between the filter and lift pump?

Empirical data from my own engine (4JH) is that 10"/Hg causes the engine to stutter a bit at high revs and 12"/Hg stops it.

If you're getting an air leak I wouldn't expect the vacuum to get as high as that.

If changing the filter has only a small effect on the vacuum then the problem is elsewhere.

My own experience with an issue that re-occured every six to nine months that with a brand new filter and using whatever snake oil I could get to clean the fuel system the best I could get was 5"/Hg. It is a long pipe run and I eventually blew it through with a small compressor (Cheapo one for inflating air beds etc) and got the vacuum down to 3"/Hg. Which is a figure I'm finally happy with.

 

[sarabande]

I had pronlems with "fuel starvation" in a Landrover. Remove and cleaned the tank, fuel lines from tanl to filter, and filter to engine. Several changes of fuel filter.. Finally, took the filter unit completely off and inspected the head unit that filter screws into. There are internal passages to the delivery and return lines.

A fragment of gasket material was found to be blocking the delivery line passage. This fragment became dislodged ( and re-lodged) depending on throttle opening and track bumpiness. The filter head was the only part that was not changed or dismantle twice. Once a new head was fitted, the engine ran perfectly.

 

[jdc]

I have had exactly the symptoms you describe. To cut the nigh-interminable story short, it turned out to be a slug of sealant about 40mm long and about 5mm dimeter which was lodging in a 90° bend in the fuel pipe between tank and primary filter. Blowing back down from the engine end of the fuel pipe always dislodged it so that was apparently ok, no leaks, random time to recur...

Dismantling the unions at all bends and peering through was the ony way I found it.

About 12 months later the same thing happened with the generator! Here's a pic

 

[Spyro]

"After air bleeding" it starts again. None of these blockage problems cause air in the system.

 

[jimi]

Stupid question, is the tank breather vent clear?

 

[vas]

Stupid question, is the tank breather vent clear?

and along this train of thought, when it dies if you do nothing, just leave it there and try firing up after 20mins, will it start?

 

[richardabeattie]

Lots of good replies, no wisecracks but nothing more from the OP?

 

[Biggles Wader]

Are the fuel lines old? Sometimes flexible hose can appear fine on the outside but goes weak on the inside and constricts the flow. A vacuum gage might help to show up any constriction.

 

[BobnLesley]

Lots of good replies, no wisecracks but nothing more from the OP?

Sorry, but I'm six hours behind you (Panama) so I've just got up and started reading the suggestions

 

[BobnLesley]

I'm currently drawing from an open fuel can which must take the breather-pipe out of the equation. I don't have access to a vacuum gauge, but might be able to get one after the weekend? Drawing from the jerry can I'm only using one old/existing flexible hose, so I'll use some new hose to make-up a replacement for that before I have my next try; it's stood overnight so I'll also try a re-start without bleeding in the first instance; I think I've tried that before, so not hopeful. If it fails once more then I'll move onto re-making all the unions with new washers again and will also remove and check/clean the secondary filter's head - again, I'm currently bypassing the primary filter, so it can't be that one. I will also try and get a new priming bulb (one of those that're used on remote outboard tanks) as like the hose, that's old/existing
We're relieved to see there aren't lots of suggestions regarding the high pressure injection pump as I know neither I nor anyone else locally can fix that; we too are increasingly of the opinion that it 'must' be an air leak, but can't understand why there's such a wide variation in the time spans before it causes a stoppage?

 

[lw395]

A mate of mine had a nightmare with air leaks.
One thing he did was to fit a clear filter temporarily after the secondary filter. Just somewhere for any air to collect until it was convenient to bleed it.
It also nailed the problem.

The other thing to consider is whether some crud has got past the secondary filter.
Some/many engines have a tiny gauze of some sort as a last ditch defense on the inlet port of the injector pump.

 

[Heckler]

I'm currently drawing from an open fuel can which must take the breather-pipe out of the equation. I don't have access to a vacuum gauge, but might be able to get one after the weekend? Drawing from the jerry can I'm only using one old/existing flexible hose, so I'll use some new hose to make-up a replacement for that before I have my next try; it's stood overnight so I'll also try a re-start without bleeding in the first instance; I think I've tried that before, so not hopeful. If it fails once more then I'll move onto re-making all the unions with new washers again and will also remove and check/clean the secondary filter's head - again, I'm currently bypassing the primary filter, so it can't be that one. I will also try and get a new priming bulb (one of those that're used on remote outboard tanks) as like the hose, that's old/existing
We're relieved to see there aren't lots of suggestions regarding the high pressure injection pump as I know neither I nor anyone else locally can fix that; we too are increasingly of the opinion that it 'must' be an air leak, but can't understand why there's such a wide variation in the time spans before it causes a stoppage?

To get to the bottom of it you need some pressure/vacuum gauges to actually see what is happening. Just for info, Ive actually seen on a youtube channel peeps with pump problems, the pump itself was actually full of bug as well!

 

[Heckler]

I'm currently drawing from an open fuel can which must take the breather-pipe out of the equation. I don't have access to a vacuum gauge, but might be able to get one after the weekend? Drawing from the jerry can I'm only using one old/existing flexible hose, so I'll use some new hose to make-up a replacement for that before I have my next try; it's stood overnight so I'll also try a re-start without bleeding in the first instance; I think I've tried that before, so not hopeful. If it fails once more then I'll move onto re-making all the unions with new washers again and will also remove and check/clean the secondary filter's head - again, I'm currently bypassing the primary filter, so it can't be that one. I will also try and get a new priming bulb (one of those that're used on remote outboard tanks) as like the hose, that's old/existing
We're relieved to see there aren't lots of suggestions regarding the high pressure injection pump as I know neither I nor anyone else locally can fix that; we too are increasingly of the opinion that it 'must' be an air leak, but can't understand why there's such a wide variation in the time spans before it causes a stoppage?

PS My money is on the old pipe or little filter going in to the pump. PPS, as a last ditch resort, taking a Bosch VE pump apart and rebuilding isnt that difficult as long as pain stakng photos etc are taken.
Stu