Yanmar 4JH57 losing fuel pressure needs aux fuel pump

[gmnord]

I have a 40 ft ketch in the Eastern Carribean, and had installed a new Yanmar 4JH57 in January 2020. The installation included a priming bulb in the fuel line near the engine fuel filter, for priming fuel after servicing the engine.

Running the engine from St Lucia to St Vincent, and later from Mayreau to Carriacou, we encountered a problem with the engine losing fuel pressure at sea, usually above 2400 RPM and often in a 1 -2m sea. I could pump the bulb 3 or 4 times and restart it, but it would fail intermittently in these conditions (but, not in an anchorage at 1600-1800 RPM in flat seas).

We deduced that the problem is that this Yanmar engine has some less than robust fuel pumps (a priming pump and a common rail pump, made by Bosch for cars). In our case, the engine must pull fuel vertically about 1.5m, and laterally about 3m.

We recently installed an auxiliary electric fuel pump between the Racor water separator and the engine fuel filter, removing the priming bulb, and that has fully remedied the problem. The engine has performed without issue in sea trial outside Tyrell Bay and from Carriacou to Prickly Bay, Grenada.

The pump we installed is a Walbro FRB 13-2 Marine Diesel lift pump, which is variable pressure based on engine demand. This pumps at 6-8 PSI and can pump up to 45 GPH - vastly more than the roughly 1/2 gal per hour our engine uses.

We presently connected the pump to 12V DC at an unused switch at the helm, but will later connect it directly to the POWER switch on the Yanmar console, so that the pump is on whenever power its on to run the engine.

Just thought I'd share, in case anyone else has seen an issue like this. It may occur only for long fuel lines that pull fuel relatively high (e.g., more than 1m) from the tank. But given the apparent dicey capabilities of the engine fuel pumps, I would say for the roughly US $200 to install an aux pump like this, one can buy some comforting confidence that the engine will not fail at sea for pumps not able to provide sufficient fuel to the engine.

[bil56]

"vastly more than the roughly 1/2 gal per hour our engine uses"

your engine pumps more than that!
it only consumes that, but pumps a lot more to lubricate/cool the injection pump, the surplus goes back to the tank, or to the filter on some engines

[gmnord]

Yes, you are right Bil56. I neglected that point.

As I understand it, at cruising RPMs in the upper 2000s, these engines can return 40-60% of the fuel they draw, and as much as 80-90% at idle. But even returning 60%, it would require the pump to provide only about a gallon per hour for the pump to maintain a sufficient supply.

I mention the pump GPH only because some applications may require a higher flow than our installation; but, for a 4JH57 in a typical application this pump is of much higher GPH capacity than required.

More important is that this engine may require an aux pump for any installation that has a high rise of fuel (1.5m for us because the fuel tank is integrated into the keel, below the engine, with a 1m deep pickup tube). Possibly the lateral run of the fuel line may not be a concern. Additional filters in the line to the engine, though, could pose a similar problem, and could require an aux pump to maintain sufficient fuel flow.

A long time Yanmar dealer pointed out to me the issue with these pumps, so the problem is known to at least some Yanmar technicians.

[bil56]

too much suction depth, ok
but you can also have a pressure drop in line, too many elbows, a too short radius of curvature, variations in pipe diameter, ...

./.

[Russ]

You have an air leak. I have same engine same Walbori etc.

[Delaware]

Air leak. Tighten all your clamps

[Bellinghamster]

3rd vote for an air leak. Ain addition to checking all hose fittings also be sure to check your tank pickup tube/fitting. I had a similar scenario whit a Perkins - ran fine as long as the electric pump was going,. I re-terminated and checked all hose connections to no avail. I finally found the leaking pickup tube inside the tank when I replaced the fuel tanks.

Temporarily put in a clear section of hose (both suction and return lines) so you can see if bubble go by

[Russ]

Air leak guaranteed. Yes check your vent first, it's easy. After that, it gets a bit harder. I have been there with my Yanmar.
First, wrap a small piece of paper towel around EVERY fitting from tank to engine. Running the engine may do it and show damp diesel on a section where the fitting is loose. Gotta remember the diesel engine SUCKS diesel so the air gets sucked INTO the fitting and for that reason you might see nothing even thig there's a leak. IF no luck this way, don't give up. You need to get a small pump and PUMP diesel through the system preferably staring at the tank end of the hose. This WILL show a leak if it exists in the system between the tank and the engine. Yes, I did ALL this to find my leaks (2) even though I have all copper flare pipe fittings!
PM me if you need more help. It isn't likely to be anything else (except the vent, Yes I had a spider web clog one of my vents once, too, same scenario engine running stopping, etc.
Russ

[hpeer]

He doesn't have an air leak, he fixed the problem with a Walbeo pump.

I also have a deep bilge, 4JH4 TE, never had a problem. For other reasons I fitted a day tak and use the Walbro to transfer fuel to the day tank through a Racor filter.

Those little Walbros are cheap enough to carry a spare. The recommend an inline check valve for higher lift applications.

The Walbro easily self primes and with the day tank at the same height as the engine the engine pump has little to lift.

[Russ]

Nope The Walboro is placed After the filters ( as it should be) it is still Sucking fuel from the tank.and through the filter system. The fuel flows From the tank to the first stage filters to the final filter on the engine and then to the engine Lift Pump which as I said sucks fuel thus the air leak persists. If the Walboro is in the loop it should be between the filters and the engine and it’s primary filter on the engine The filters aren’t designed to have fuel “pushed” through. Usually Walboros are used as part of a fuel polishing system Not to push or suck yet more fuel to a balky engine. The engine pump is more than adequate for the demand of the engine. As someone said correctly the engine uses a tiny amount of the fuel passing through it

Sorry the Walboro does not eliminate the air leak. Trust me I’ve been there.