Air in Fuel System -- Yanmar

[Dockhead]

I had a problem with my Yanmar 4JH3 HTE a few years ago that just about drove me crazy. Engine would not rev over 3000 RPM (eventually, over 2500).

I went so far as to replace the injectors, took the injection pump off to be bench tested, and nothing worked.

Also had the turbo checked out, washed the turbo, etc.

Bled the fuel system repeatedly.

This went on for about a year.

Finally I changed the fine fuel filter on the engine (which was not due), and the problem disappeared, and has not reappeared in several years.



NOW, I just installed the Maretron fuel flow sensors in the supply and return fuel lines, which I bought three years ago and never got around to installing.

I didn't bother to bleed the lines when I started it up again, as very little fuel went out of them, and I thought it might self bleed.

Well, it did not. The engine started and ran, but there was obviously air in the lines.

So since it was on my list anyway, I changed the fine fuel filter. For some reason, I couldn't bleed the new filter using the hand pump. So I started the engine briefly and let some fuel flow through, and then I was able to bleed it with no problem.

But now the engine behaves like it did back then. It won't rev much over 2500 RPM and misses over that.

I have checked and rechecked that everything is air tight, tightened the filter, bled it again.

Nothing works.

A couple of questions:

1. Do I need to bleed the high pressure lines, and can I do that with the engine running? I'm single handed so would be complicated to crank with stop button pushed while bleeding.


2. Are these engines very sensitive to restrictions in the fuel system? The Maretron units do of course produce some resistance.


Grateful as always for any tips.

[Cheechako]

Some engines are sensitive to restrictions, or vacuum build up in the lines. I wonder if the Maretron sensors are causing that? How about an electric fuel pump just after the tank to boost pressures? Handy for bleeding anyway.

[Dockhead]

Originally Posted by Cheechako

Some engines are sensitive to restrictions, or vacuum build up in the lines. I wonder if the Maretron sensors are causing that? How about an electric fuel pump just after the tank to boost pressures? Handy for bleeding anyway.

I might do it. Are there any electric pumps which allow free flow through them when they're off?


Meanwhile I'm going to re-make the connections to the sensors, and enormous PITA, but I'm not quite happy with the hose clamps, which are not exerting even round pressure. Tomorrow I'm going to toss them and get some different ones, re-cut the fuel hose ends, and try again.

A few more hours down the drain

I have a long list of things to do, and this damned little job is sucking up all my time

[twinboat]

If it's running there is no more bleeding needed. They self bleed.

What you need to do is backup a step. Remove the flow sensor from the fuel line and check the running RPM s.

If your prime pump don't work, turn the engine a half a turn and try again. Some are cam driven and if on the high spot, will not pump by hand.

All fuel lines need to fit tight in any fittings you add to stop air from being sucked in. Just clamping a loose fit won't work.

Anything before the pump won't leak fuel but will let air in.

Good luck

[Panope]

Dockhead,

I'll mention that the ability of Panope's 3JH3E to 'self bleed' is remarkable. If it will start, it will bleed itself.

Edit: twinboat beat me to it.

Assuming your injection system is the same as mine (big assumption since I am normally aspirated), then I (also) would look at the possibility of restrictions or low fuel pressure first.

Steve

[Cheechako]

Originally Posted by Dockhead

I might do it. Are there any electric pumps which allow free flow through them when they're off?


Meanwhile I'm going to re-make the connections to the sensors, and enormous PITA, but I'm not quite happy with the hose clamps, which are not exerting even round pressure. Tomorrow I'm going to toss them and get some different ones, re-cut the fuel hose ends, and try again.

A few more hours down the drain

I have a long list of things to do, and this damned little job is sucking up all my time

My general understanding is they do, but maybe someone will chime in. The last one I installed was just a NAPA auto parts one, cheap and worked fine. The other option is a 3 way valve after the pump and a T before. Oh good ... more plumbing!

[Dockhead]

Originally Posted by twinboat

If it's running there is no more bleeding needed. They self bleed.

What you need to do is backup a step. Remove the flow sensor from the fuel line and check the running RPM s.

If your prime pump don't work, turn the engine a half a turn and try again. Some are cam driven and if on the high spot, will not pump by hand.

All fuel lines need to fit tight in any fittings you add to stop air from being sucked in. Just clamping a loose fit won't work.

Anything before the pump won't leak fuel but will let air in.

Good luck

OK, thanks. And that's what I'll do.

I suspect the hose connections. The hoses fit very tight on the nipples -- they were a right bitch to get on in an awkward position. They have aggressive barbs on them unfortunately. But the hose clamps are slightly too large and have a large saddle which looks like they're cutting the hoses or maybe distorting them, which could be letting air in.

What I will do is bypass the sensors with a couple of pieces of 3/8" copper and see if it runs ok. Then I will know whether it is the connections at the sensors or not.

Then if that's ok, then I'll remake the connections using better clamps.

Does that sound like a rational way to do it?

[ericoh88]

Dockhead,

I might try a few things here.

1. What type of "fine fuel filter" are you using?

The Racor FG500 with replaceable filters are notorious to leak air into the system. Use new o rings.

2. I will try to put a clear hose to confirm if there is air bubbles coming in.

3. Temporary replace the inline fuel sensor with a straight pipe of similar size, ie copper or aluminium pipe, to do a test.

4. Install a vacuum gauge to monitor the resistance in the fuel line.

5. Tony from seaboard use this

Squeeze Bulb Priming Kit - Seaboard Marine

Maybe use a 12v fuel pump instead of the hand bulb pump.

Hope you catch this monkey

Eric

[Dockhead]

Originally Posted by Panope

Dockhead,

I'll mention that the ability of Panope's 3JH3E to 'self bleed' is remarkable. If it will start, it will bleed itself.

Edit: twinboat beat me to it.

Assuming your injection system is the same as mine (big assumption since I am normally aspirated), then I (also) would look at the possibility of restrictions or low fuel pressure first.

Steve

OK, that's very useful indeed.

My pump is quite similar and if yours does this, then mine ought to also.

I will set aside bleeding for the moment and concentrate on the hose connections.

If it's not the hose connections, then I'll go through the filters again, check the gaskets. My lift pump is integral with the injection pump and sucks through the filter, so air leaks can happen anywhere there.

[Dockhead]

Originally Posted by ericoh88

Dockhead,

I might try a few things here.

1. What type of "fine fuel filter" are you using?

The Racor FG500 with replaceable filters are notorious to leak air into the system. Use new o rings.

2. I will try to put a clear hose to confirm if there is air bubbles coming in.

3. Temporary replace the inline fuel sensor with a straight pipe of similar size, ie copper or aluminium pipe, to do a test.

4. Install a vacuum gauge to monitor the resistance in the fuel line.

5. Tony from seaboard use this

Squeeze Bulb Priming Kit - Seaboard Marine

Maybe use a 12v fuel pump instead of the hand bulb pump.

Hope you catch this monkey

Eric

And even more useful information! Thanks very much. This forum is the greatest.

Indeed, my primary filter is a dual Racor 500. I had never heard that they cause air problems -- that's interesting news. I actually checked them and one of the filter chambers was mostly empty. I wonder if that could be related?

Maybe before remaking the hose connections, I'll change the Racor filters, fill carefully with fuel, and install new seals and o-rings.

Another thing I could do is just bypass everything with a new piece of hose directly to the secondary filter from the Racor.

Thanks; I think I'm starting to get a grip on this problem now.

[ericoh88]

Originally Posted by Dockhead

Indeed, my primary filter is a dual Racor 500. I had never heard that they cause air problems -- that's interesting news. I actually checked them and one of the filter chambers was mostly empty. I wonder if that could be related?

The culprit is the gasket on screw handle

[Joe Kiernan]

You've gotten some good advice here! The Racors are infamous for air leaks, particularily at the "T" handles, most people don't realize they have a seal under them.

Installing a bit of clear hose temporarily as close to the engine lift pump will tell all as regards air ingress downstream.


It's worth the time to "Y" in a small 12 v. lift pump as close as you can get to the fuel tank with an inline shutoff valve on the other side of the "Y" to give you the ability to pressurize the suction side (the valve will stop the pressurized fuel from returning to tank). This accomplishes 2 things, #1 allows you to change filters and bleed the filters all the way to the injection pump in a matter of moments and, #2 provides a "emergency" lift pump if your engine driven one ever give up the ghost. (Had that happen to me once in the Gulf islands in CA and it got me home)

[twinboat]

I think your getting close with the low filter level on the Racor. Air would be getting before or on it.

Adding fuel pumps shouldn't be nessessary. It worked since new, so something changed.

Adding pumps just adds things to give you trouble and could mask other problems.

If it ain't broke, don't fix it.

[leftbrainstuff]

Originally Posted by Dockhead

I had a problem with my Yanmar 4JH3 HTE a few years ago that just about drove me crazy. Engine would not rev over 3000 RPM (eventually, over 2500).

I went so far as to replace the injectors, took the injection pump off to be bench tested, and nothing worked.

Also had the turbo checked out, washed the turbo, etc.

Bled the fuel system repeatedly.

This went on for about a year.

Finally I changed the fine fuel filter on the engine (which was not due), and the problem disappeared, and has not reappeared in several years.



NOW, I just installed the Maretron fuel flow sensors in the supply and return fuel lines, which I bought three years ago and never got around to installing.

I didn't bother to bleed the lines when I started it up again, as very little fuel went out of them, and I thought it might self bleed.

Well, it did not. The engine started and ran, but there was obviously air in the lines.

So since it was on my list anyway, I changed the fine fuel filter. For some reason, I couldn't bleed the new filter using the hand pump. So I started the engine briefly and let some fuel flow through, and then I was able to bleed it with no problem.

But now the engine behaves like it did back then. It won't rev much over 2500 RPM and misses over that.

I have checked and rechecked that everything is air tight, tightened the filter, bled it again.

Nothing works.

A couple of questions:

1. Do I need to bleed the high pressure lines, and can I do that with the engine running? I'm single handed so would be complicated to crank with stop button pushed while bleeding.


2. Are these engines very sensitive to restrictions in the fuel system? The Maretron units do of course produce some resistance.


Grateful as always for any tips.

Have you introduced an additional suction side pressure drop?

Also you need to bleed air from the injector pump to the injectors. Any air on the high pressure side will tend to cause an issue.

Always bleed before starting if you've introduced air on either the suction or pressure side. Rule number one of diesel fuel systems.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[Stu Jackson]

Originally Posted by Cheechako

My general understanding is they do, but maybe someone will chime in. The last one I installed was just a NAPA auto parts one, cheap and worked fine. ...............

You're right. We have an electric fuel pump that runs all the time. Our fuel tank is above the engine. I usually keep my tank half filled and can (and have) turned my ignition key off for one reason or the other and the engine keeps running. On our boat some skippers have reported that once the fuel tank is less than half full the engine may sputter, but I've never experienced that (in 18 years). So, between the "head" of the higher tank and the siphon effect, even with the fuel pump shut off the fuel flows. It's a Facet pump on a Universal M25 21 hp 3 cyclinder naturally aspirated engine. Good luck.

PS - A good friend once advised me: "Only do one thing at a time, so if it doesn't work, you'll know what it is."