Yanmar experts

[sailaway78]

A 3gm Yanmar. Engine has approx. 1500 hours. It always runs perfect. But when it sits for two or three weeks without starting it up, will not start till the system is bled. Have looked and looked and find no air leak, or anything that I would think would allow air into the system. I have noticed that the return to the tank has almost no flow, just a very tiny trickle and that not all the time. Is there something that this would indicate is a problem, or is this normal for this engine. I consider myself to be pretty mechanically inclined, but this thing has me totally stumped. And I am anal enough that the idea of not being able to fix it myself really irritates me. IDEAS, SUGGESTIONS

 

[Ross]

Log onto Boatdiesel.com forum and talk with the experts

I like that forum well enough to pay the subscription fee of 25 bucks a year.

 

[sailortonyb Allied Mis]

Had a similar problem

It turned out that i had a leaking injector pump.Verry slow leak. Look in bilge for signs of fuel.My engine would start every other week, but if i went into 3rd week it wouldnt start. $1300 later and all is well again.

 

[Rich (P303)]

Is that you...

pouring in fuel... to start your engine? Wow... its got to be air or fuel... but then again I am not a mechanic. Try opening up the fuel cap before you start... after you have been away for a while. Vaccuum?I know... stupid suggestion. I am grasping at straws. Nothing gained... nothing lost.

 

[RichH]

Couple of things ..... usually air leaks.

Yanmars dont have much 'return flow'.Possibilities:Leakey compression fittings on the fuel system. Compression fittings are designed for ONE TIGHTENING ONLY ... then for 'proper' usage if you loosen you 'should' trim back and cut away the copper tube section that was 'compressed' or deformed ... all the way back to undeformed tube, etc. and then install a NEW ferrule. Easier/Simpler: Retighten every compression fitting in your fuel system from the tank all the way to the injection pump. A leakey compression fitting will allow air to enter the line. Ditto cracked compression / flared fittings. If you ever used Teflon tape or dope on a compression fitting or flared fitting (as an 'aid' in sealing a leaker) .... they ultimately will leak as these are all metal-to-metal seals and the teflon will eventually 'creep' out of the seal.In all these 'leakers' air will enter through the flaw and migrate to the highest unrestricted level of the system ... if the air migrates towards the tank it can 'lift' oil back to the tank .... all done in very slow motion .... if the air migrates towards the engine you will find air in the engine mounted 'guard filter'. If the valves in the lift pump are not making a perfect seal you might be getting some gravity 'drain back' ... if the engine is slightly higher than the tank. Test for this or similar 'drain-back' by shutting off the tank's exit valve when leaving the boat for long term and compare. Ditto if the lift pump diaphragm is developing a pin-hole leak.If you ARE suspicious of a 'leaker' allowing air to enter the low pressure side of the fuel system: Into the gage port on a Racor ... mount a tee to the gage port then a gage then a vacuum rated cockvalve.... close the tank valve, apply vacuum to the system through the gage/tee then close the valve ...... when you come back several hours later and the gage has changed back to zero - guess what? ... you have an air leak in the low pressure side somewhere between the tank and the injector pump. To help SEE where the leak is - close the tank valve, pressurize the system through the gage/tee to 10-15 psi, shut the valve .. come back a few hours later to find the 'wet spot' . If no 'wet spot', and the pressure has relieved then disassemble the lift pump and carefully examine the diaphragm for a pin hole. Ditto fuel injectors that are leakey ..... cracks in the injector pump, injector body. When was the last time you sent the injectors to a shop for exam/evaluation? And the most costly and most difficult to find ...... GREMLINS. Yanmars will usually start up even with a goodly 'slug' of air in the system ..... so the leak should be quite obvious once you get 'close' to it.

 

[don macphee]

don

NEEDS NEW HAND PRIMING PUMP. LOCATED ON STBD SIDE. THIS KEEPS YOUR FUEL PUMP- PRIMRED AND FULL OF FUEL. ONLY 2 BOLTS TO REMOVE $90.00DON

 

[sailaway78]

Thanks all

I have tried just about everything listed here, with the exception of doing a leak test using a vacum gage. I was somewhat concerned that the lack of return flow might have something to do with it, but since Rich said they don't have much, and I do respect what he says, am just about back to square one. Guess the next step is a leak down/pressure check. I am beginning to suspect the lift pump, has a small leak in the diaphram. There is no leak at the pressure pump that I can tell. Last time out, I checked for even the slightest leak, and had to run it all day getting back around our busted bridge. As I said, once running, it never misses a beat. And I do not have a hand priming pump. This boat has two big WIX filters, and an electric pump, that I normally don't run, except to bleed the system. So, it's back to the drawing board.

 

[jk kudera]

In your last response

You said you have an electric pump you rarely use, if it is in line, will the engine start if you use the electric pump to supply fuel? If it does, you can suspect the mechanical pump is the problem. Also, is it possible the mechanical pump is leaking fuel into the engine oil?

 

[Pete]

Maybe no air leak at all

A Yanmar service bulletin was issued for this same problem due to a check valve not being installed. The problem will manifest itself only after engine has been sitting a while, once started it will run and restart all day until it has sat a while again. You did not mention if your's will run OK once fuel is bleed but if so I would suggest you check this out. There are other postings and links in the archives or try yanmarhelp.com (see attached link). I think there was a link on the Catalina web page also. At any rate sounds like the cure for you symptoms and was a issue for certain years on the 3 gm engine in particular the fuel will backflow and the pump will lose prime. Mach Boring may also be of some help I know they are located in New Jersey but have other location may want to try there web site also. Good Luck !!