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Discussion Starter #1
I have a Yanmar 3GMD on my boat that was recently professionaly rebuilt and ran 100% perfectly all of last year and I used it a lot. This year it started right up for the first time and ran perfect. However since then I have changed the oil and the secondary fuel filter which is a Racor located in a cabinet under my sink. The engine fired back up fine.

However it seems that the past few times I go the boat the engine is having a lot of trouble starting. It turns over fine but it takes me a while to get it going - more than it ever has before. Today it took 3 attempts for about 5-7 seconds each before it finally went. Once it runs, it runs perfectly and if I shut it down and wait 10 mins or so it starts right back up but if I leave the boat and come back the next day I have the same trouble.

Does this sound like an air in the fuel lines sort of thing? The only thing I can think of was I did something or air got in somehow when I changed the Racor but then once I get it started why would the engine run fine?

Also the previous owner placed a pressure guage on one of the outlet sides of the Racor and I did notice it reads 0pressure. I tried loosenign the vent screw on the top of the racor and pumping the fuel prime switch on the engine but never saw any fuel or air bubble leave the vent screw ontop of the Racor. Is there another way to bleed the fuel filter?

Thanks
 

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It a good idea to bleed the whole system. If air is present some where it might be causing fuel feed problems to the pump while starting. That air might stay some where else and return back to original blocking point after the engine is stopped.
 

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Sounds like a fuel delivery problem or you have air in the line. If you vent the Racor (primary filter) then pump the lift pump, you are probably putting air into the system. The racor is under a slight vacuum so opening the lid hold down screw and pumping the lift pump can draw air into the system.

Open the vent on the secondary filter on the side of the engine (pressure side of the lift pump) and activate the lift pump to purge air. If air has gone past the secondary filter you will have to purge up to the high pressure pump and maybe even to the injectors. Consult your Yanmar manual for bleeding the HPOP and injector lines.

Your Racor should have 0 pressure (maybe even a slight negative pressure) as it is between the lift pump and the fuel tank, unless you have a boost pump (not common).

If you get little or no flow from the secondary filter while bleeding, your lift pump may need to be replaced. Your symptoms sound similar to mine when the diaghram in the lift pump went out.
 

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Discussion Starter #5
Thanks for the suggestions so far. I have already tried bleeding air at the fuel filter that is connected directly to the engine. I tend to think the problem is at the Racor fuel filter since that is the one I changed out and I can't figure out how to bleed it. Do all Racor's have their own litlte pump on them? I couldn't seem to find mine.

Secondly if the problem is back by the Racor, would bleeding the fuel filter on the engine eventually force the air out?
 

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Yes if you should be able to bleed the air out at the secondary filter however the Racor should have it's own vent. One tip I picked up here and put on last year was to install an outboard type priming bulb just where the line comes out of the tank.
Then to purge air all you do is go to the first filter and open the vent, pump the bulb till you see solid diesel come out. Go to the secondary filter and repeat. On my 2GM I have never had to bleed off at the injector.

If you engine starts and runs fine for say 15 minutes or so then I would think you do not have air in the lines.

Another thought you could have an air leak, check all you connections.

Gary
 

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Always check the simple things first. Is your filter cartridge on tight and is the gasket seated properly ?
 

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on a racor filter without a priming pump on it , installing a ball valve on the inlet side of the racor makes bleeding the air easer. to change the filter element, close the valve, drain the racor, & change the filter. then fill the filter with fuel, open the valve & pump the engine pump to bleed the air out at the engine filter. i have a racor 500 . it does not have a priming pump on it. i have an electric pump between the tank & the racor which makes bleeding the system easy.
 

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If the engine does start, but

not on the first 5 seconds, then it is not air, at least not likely, since the motor stays on once you get it going.

When diesels get below say 50 deg F and they don't have Glow Plugs, like a lot of Yanmars, they take a little longer to catch. You're located in LI area, it's April and still cool out, so that is more likely your issue and not air. Also supporting this theory is that once you get it hot, it starts right up, but you let it sit for a day, it is harder to start again. Once the outside and water temps go up little, I bet you motor fires right up.

Last year I fired my motor right up after a 5 month slumber on a the hard on a 75 deg day. 3 days later it was in the water (40 deg F) and the air was 41 and it took a few attempts to get her going.

DrB
 

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It sounds like you do have an air leak. First you need to start at the tank and check every connection. Make sure every clamp is snug and the filter is properly put together. Next, you need to properly bleed the entire fuel system. I mean no offense to anyone, but none of the posts above tell you how to do it right. I'm going to look for an old thread that provides the right procedure, and post it here in a few hours.
 

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This is such a common question that I think it deserves a sticky thread or faq. I'm sure the following text could be improved, but I think it's a good start.

You need to be able to identify a few parts of the fuel system. Follow the fuel hose from the primary filter (often a Racor) to the engine. First, the hose goes to the low-pressure fuel pump (also called a lift pump). On a Yanmar this will be a mechanical pump. Then follow it to the secondary fuel filter, which is attached to the motor. From there find the fuel line that goes to the high-pressure fuel pump. So far you have traced the low-pressure fuel system. (If you are having trouble finding the high-pressure pump you can trace the metal fuel lines back from the injectors.)

If you introduce air into the low-pressure fuel system, for example, change the fuel filters, you should bleed the air from the low-pressure system before trying to start the motor. If you ignore this advice you will force air into the high-pressure system and then you have to bleed that as well. Also, when changing filters, do not fill the filter with fuel before reinstalling it.

To bleed the low-pressure system open the vent on top of the secondary filter bracket until you can see the hole in the side of the threads. Find the low-pressure fuel pump and operate the small lever on its side. Only the last ½ inch of travel pumps the fuel. Move the lever back and forth until clear fuel comes out of the vent screw on the filter. This will take many strokes if the filters have been replaced. (Use a cup or a rag to catch the fuel coming out of the bleed screw.) When you have good clear fuel with no bubbles, close the screw. If operating the lever pumps no fuel (there is no resistance operating the lever) you may have to turn the engine over a tad (with the kill switch out). This will move the pump cam off the lever. Then find the inlet into the high-pressure pump. The hose comes from the secondary filter. Loosen the banjo bolt a number of turns, and then once again operate the lever on the fuel pump. It should only take a few strokes to get clear fuel at the high-pressure pump inlet. Then tighten the banjo bolt. The low-pressure system should not be air free.

The high-pressure system consists of the high-pressure fuel pump, the fuel lines going to the injectors, and the injectors. Normally you do not need to bleed the high-pressure system after changing filters, just the low-pressure system.

Bleeding the high-pressure system goes like this....

Bleed the low-pressure system first. Then, open the connection at each injector 1 full turn (open all of them). Turn the key on and crank the engine over until fuel spits from the loosened connectors. Do not pull out the kill switch! The engine cannot start like this so don't worry. Then firmly (these things run at 2,000 - 3,000 psi) re-tighten each injector connection. There is no hurry, the fuel cannot “leak-back” while you are doing this step. That's it - start it up! (If it doesn't start, bleed the low-pressure system again, and then the high pressure system.)
 

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Hi Nick,

If you engine runs fine, you don't have a problem with air in the lines. If you do have air in the fuel line, the engine won't start until the air is bled out. Since your engine does start, runs, and keeps running, bleeding won't do anything.

It is possible that you don't have a good seal somewhere in the fuel lines, and when the engine is shut down, air gets in. Take a look at the things you touched, make sure you got all the gaskets installed properly. When the engine is running, look for fuel leaks, that is one way to know if a gasket is bad.

Lastly, the pressure gauge is most likely a vacuum gauge. As the fuel filter gets dirty, it requires more and more suction to draw fuel through it. This will be shown on the vacuum gauge and will let you know that it's time to change the fuel filter.

One final point, there are many many boaters who would LOVE to have their engine start in 5-7 seconds. On my boat, when it's cold (below 60), I need to energize the glow plugs for 30 - 60 seconds, then crank the engine for at least 10 seconds before it runs. So maybe, as another poster mentioned, it's just too cold.

Good luck,
Barry
 

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Well obviously people disagree on this one. I still believe you have a small air leak. Hence the extra cranking after the engine sits. Here's how to test the theory. After letting the engine sit, bleed the system before trying to start it. If it fires right up after bleeding it, you have an air leak. If there is no change and it still requires the extra cranking time, you don't.
 

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Discussion Starter #14
SteveNMD - Thanks very much for the detailed post on how to bleed the system. How come you don't have to bleed the secondary fuel filter (racor) before going to the primary on the engine? Also why don't you recommend putting fuel back into the filters after changing them?

Barry - Thanks as well - I am hoping it is just a cool air thing because it does start right back up after it has been running.

I guess either way I will find out but thaks again for all the help everyone
 

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BTW, over-tightening banjo bolts is a common cause of air leaks into a fuel system... ;) so replacing the banjo bolt compression washers can often fix it...if you don't over tighten them.. :)
Bleed at the banjo bolt on top of the injector. Open the bolt a little and pump. If you see foam you have air. When you pump and see just fuel the air is gone. You can also bleed at the top of secondary filter. The little bolt right on top.
 

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SteveNMD - Thanks very much for the detailed post on how to bleed the system. How come you don't have to bleed the secondary fuel filter (racor) before going to the primary on the engine? Also why don't you recommend putting fuel back into the filters after changing them?

Barry - Thanks as well - I am hoping it is just a cool air thing because it does start right back up after it has been running.

I guess either way I will find out but thaks again for all the help everyone
Actually the Racor is usually referred to as the primary filter. You don't have to bleed this first because in a "normal" setup you have to suck the fuel through it using the low-pressure pump. Unless the primary filter has a built-in hand pump there is no way to bleed it by itself. The built-in pumps are nice, but not necessary at all.

The reason not to fill the filters first is because it can cause air to be forced into the high-pressure system. I can't tell you how many times I've seen this happen... You change the fuel filters and topping them up with fuel to avoid so much manual pumping. Then you start the bleeding process. However since there is clear fuel in the hose from the Racor thought the lift pump and up to the secondary filter (the one attached to the motor) you get clear fuel spouting from the vent screw very quickly. Happy with your brilliant idea to pre-load the filters you move on to the next bleed point at the high-pressure pump inlet. Again, a few strokes and you think you are done so you button everything up and fire the up the engine. It starts right up and you smile proudly. After about 5 minutes of running the engine sputters and quits. What happened is that there was a big slug of air in the top of the Racor (even though you mostly filled it). This slug of air travels through the system and ends up in the high-pressure side, which is when the engine quits. Now you have to start from square one and bleed the low side and then the high side. I find it easier to just stick to the procedure pump the lever as needed. Yes, you can pre-fill a little fuel, without causing problems, but I don't think it's worth the trouble.

Regardless if you are having problems with air in your fuel system or not at the moment it's good to know how to bleed the system. Practice in your slip so you can do it easily at sea.
 

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nk235, does your fuel system leak? If not, you probably don't have an air leak.

You have not mentioned what the fuel flow was like when you bled the secondary filter (the 2 micron filter at the engine) with the lift pump.
Sometimes, when the lift pump starts to lose performance, the engine will be slow to start at first but on subsequent starts it will fire right up. Until it has a chance to sit and lose the prime again. Once fuel is flowing to the high pressure pump it will draw fuel on it's own. On older engines, the bottom of the lift pump had a weep hole that would leek if the pump diaghram went bad. CG regulations outlawed those types of pumps so now the system is closed and won't leak or draw in air that kills the engine when the pump is bad.

I'll go along with what's been said earlier. If your lift pump is working (you get good strong squirts when bleeding from the banjo on top of the filter) and you are getting clear fuel when bleeding, there is probably nothing wrong and the slow starting is normal for the season.

For the record. I would still prefill the Racor. If you don't, all of the air volume in that filter will have to be bled at the secondary, with the lift pump which does not have much flow volume. If you are concerned about air in the fuel lines during filter changes, either install valves or mount the filter in a slightly elevated position so the fuel doesn't run out of the hoses when you drain the Racor bowl.

Most of my fuel system is mounted below the top of the fuel tank. Before I open the fuel system I just make sure the tank is topped off so I can gravity bleed before I bleed the engine with the pump.
 

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If you engine starts and runs fine for say 15 minutes or so then I would think you do not have air in the lines.

Another thought you could have an air leak, check all you connections.

Gary

On my 2GM it takes a lot longer than 15 minutes at 1000 to 2000 RPM to run air through the system. Closer to 30 to 40 minutes. Hard to believe, but I learned the hard way!
 
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