Air in Fuel System -- Yanmar

[01kiwijohn]

If the engine "starts instantly and runs smoothly....." it is not likely to be an air leak, what ever the speed.
Your compression type fitting (olive) idea is ok, done properly it will not leak.

[Dockhead]

Originally Posted by 01kiwijohn

If the engine "starts instantly and runs smoothly....." it is not likely to be an air leak, what ever the speed.
Your compression type fitting (olive) idea is ok, done properly it will not leak.

Why else would it cut out then, though?

[transmitterdan]

Most of these have a max speed adjustment screw on the throttle. Check to see if some piece of debris is preventing the throttle going to WOT. Don't adjust the screw though unless the locking nut has come loose. It is a factory setting.

[01kiwijohn]

Let me repeat:
"Now, you don't say how many hours on the engine so, assuming the external system integrity is good, the problem could be the in the delivery check valves, in the top of the injector pump; not usually a job for a home-handyman type. This usually shows up at over 3000 hours or so."
Good luck, and let us know if that helps.....or not.
If you want to verify there is/or is not, air getting in; run the engine for a while, or until it gives trouble, then, once stopped, open the bleed screw on the injection pump housing and see if there is any air in the fuel at that point.
From the symptoms described, it may not be an air problem.

[Dockhead]

As soon as I had the proper fuel hose, I tried running the engine from a fuel jug via a direct hose to the secondary filter. Bingo. Ran perfectly.

So quickly bypassed the supply side fuel flow sensor and -- bingo.

Runs like a Swiss watch, smooth and sweet, right up to 4000 RPM.


It turns out that I bought the wrong nipples for the fuel flow sensors -- for 3/8" fuel hose rather than 8/16 (5/16"). That's why it was so hard to get the hose onto the nipples -- wasted two extremely unpleasant evenings wrestling the hoses onto the wrong nipples -- with one hand.

Now I did get them on, so why this would cause this problem I don't know. I have ordered new nipples and will try again in a few days. My guesses:

1. Somehow stretched or split the hoses to cause an air leak
2. The nipple leaks where it's screwed into the sensor (I used thread compound, but it was kind of old -- maybe didn't work).
3. Crack or other defect in the sensor
4. My engine just doesn't like the resistance created by the sensor.


In any case, boat is again seaworthy (hurra!), and the rest I'll figure out in a few days when the new nipples come.

Thanks everyone for the whole education on fuel systems! The only bright side of this horrendous waste of time, is that I've learned an awful lot about fuel systems.

[Dockhead]

Originally Posted by 01kiwijohn

Let me repeat:
"Now, you don't say how many hours on the engine so, assuming the external system integrity is good, the problem could be the in the delivery check valves, in the top of the injector pump; not usually a job for a home-handyman type. This usually shows up at over 3000 hours or so."
Good luck, and let us know if that helps.....or not.
If you want to verify there is/or is not, air getting in; run the engine for a while, or until it gives trouble, then, once stopped, open the bleed screw on the injection pump housing and see if there is any air in the fuel at that point.
From the symptoms described, it may not be an air problem.

2300 hours.

Apparently no problem with the injection pump.

[Cheechako]

Hmmm.... I seriously doubt that a too big fitting would be a problem with leaking if you actually got the hose on there. The culprit sounds like your flow sensor itself causing restriction. That's my guess anyway. I guess we will find out soon!

[Dockhead]

Originally Posted by Cheechako

Hmmm.... I seriously doubt that a too big fitting would be a problem with leaking if you actually got the hose on there. The culprit sounds like your flow sensor itself causing restriction. That's my guess anyway. I guess we will find out soon!

We'll soon see.

But not necessarily fitting being too big -- could also be bad seal between hose tails and sensor.

Or a crack or defect.

If it's restriction, then I guess I'll need to add a booster pump.

[01kiwijohn]

Glad to hear it, congratulations. Oh, and if you got the 5/16 hose onto 3/8 barbs I'll bet you're good at crushing beer cans, even those steel ones!

[Dockhead]

Originally Posted by 01kiwijohn

Glad to hear it, congratulations. Oh, and if you got the 5/16 hose onto 3/8 barbs I'll bet you're good at crushing beer cans, even those steel ones!

I can hardly describe what kind of torture that was.

I must be a special kind of stupid for not realizing that it wasn't normal.

The thing is, I couldn't REACH them properly. So I spent two entire evenings wrestling them on WITH ONE HAND, while lying half in the engine room, wedged between the engine and the generator platform column, holding myself up with the other hand, breathing diesel fumes, sometimes laying my head on the alternator.

So my great achievement today is successfully getting right back to where I was when I started

Still it's a hell of a lot better than where I was yesterday.

[01kiwijohn]

Don't beat yourself up, there are those of us here who have made MUCH bigger mistakes.
You live...you learn. Good luck

[sartorst]

Some of those barbs on the nipples are knife sharp! my preference is the less aggressive
ones. The other day I was doing some fuel line work and when installing the nipples I was wishing that they were not so sharp afterwards of course one had to be removed! I spent about 10 minutes with veins bulging trying to get it back off and once off was hoping the tailings from the hose did not go somewhere they should not

[sartorst]

Originally Posted by twinboat

I have a disaster waiting to happen engine. I remove the old spin on filter, put a spot of oil on the gasket of the new one and screw it on, hand tight.

Next, I stroke the little lever, fitted to the 32 year old engine mounted, camshaft driven, diaphragm pump until I feel some resistance. A few more strokes and I turn the key and the engine starts quickly, as usual.

I have run the engine until it stalled from clogged filters many times and either switched the dual Racor or changed the spin on. A few strokes on the disaster pump and off I go. I don't have air leaks in my fuel lines.

In the 8 years I have owned the 1984 boat, I loosened the fuel injector lines one time. That was to replace one due to failure. Still didn't bleed it to start i

For 30 years I serviced and repaired diesel powered equipment. In that time I recall bleeding a hand full of engines. That was because I had done major work on them. Of course I always primed the fuel system according to the manufactures recommendations.

And as a said before, I would get enough cylinders firing to keep it running until the rest bleed out by themselves.

There are only so many times you can loosen and tighten injector nuts before they crack and leak.

Your engine may be a rare one that needs bleeding every time you service it but it is not the normal way to start most.

It sounds like you don't or can't prime your system. If that's the case, starting it with empty fuel filters, will cause it to run on the fuel remaining in the high pressure lines until it is gone. Then bleeding may be nessessary.

All diesels are not alike.

Have a good day.

Improper use of words on my part sorry! prime / bleed, I did not mean to imply that injector lines need to be bled! And if we are tooting our horns I have been doing this for 40 years professionaly

[Dockhead]

Originally Posted by sartorst

Some of those barbs on the nipples are knife sharp! my preference is the less aggressive
ones. The other day I was doing some fuel line work and when installing the nipples I was wishing that they were not so sharp afterwards of course one had to be removed! I spent about 10 minutes with veins bulging trying to get it back off and once off was hoping the tailings from the hose did not go somewhere they should not

I don't even bother trying. I just cut the hoses off that type of barb.

The Yanmar hose tails are just straight pipe with a little bulb at the end. Now those you can get hose on and off with no problems.

[petter5]

Be sure to correctly size your fuel lines and filters, using good quality material.

One thing I have seen several times is fuel tanks with suction pipes threaded in the tank cover leaking air in the threads , can be extremely difficult to diagnose.

One thing that would not fix the system, but fix the symptoms is to mount a so called "Tiger loop" to remove the air from the fuel:
Tigerloop Article

The article in the link above also explains a lot of theory around the problem with air in diesel.
Tiger loop works fine for boat engines as well :-)