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Old 05-07-2022, 05:23   #1
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Help Yanmar 4by3 wonít start

Cruising along and it just died. Water separator had bad fuel in it so I changed it and the big primary fuel filter. Still wonít start. No engine alarms.

It cranks fine, all fluids are good, oil pressure gauge reads while cranking. I cracked big nut on top of large primary filter and fuel comes out.

Any ideas? Fuel relay? I found some relays in the black ecu box but not sure which one is fuel?

Iím am south of crooked island cruising on one engine heading to crooked island marina hoping they have services there
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Old 05-07-2022, 06:02   #2
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Re: Help Yanmar 4by3 wonít start

I found the fuses and they are all good
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Old 05-07-2022, 14:24   #3
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Re: Help Yanmar 4by3 wonít start

When you say "bad fuel", do you mean it had water in it, or muck/sediment?

If it cranks but won't fire, then it's likely not getting fuel. Have you checked/changed the secondary fuel filter and the lift pump screen?

Did you get air in the system when you changed the primary? Have you tried bleeding/purging the fuel lines?
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Old 05-07-2022, 15:00   #4
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Re: Help Yanmar 4by3 wonít start

Yes water and some sediment in the fuel separator, it’s electronic fuel pump so no screen or lift pump. I cracked the bolt on top of the primary to bleed it. Injector lines I haven’t tried yet because they are very difficult to get to and I don’t have the right wrench for them
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Old 05-07-2022, 16:36   #5
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Re: Help Yanmar 4by3 wonít start

This is a common rail computer controlled engine not the familiar mechanical pump and injectors so the problems are bit harder to solve. Certainly the primary fuel supply should be carefully inspected and tested for air leaks and restrictions but if this all checks out and you have an air free supply of clean fuel the diagnosis becomes a bit more difficult because it is very possible that one of the sensors is the culprit, sometimes itís one of the two on the actual common rail but you really need to access the error codes to establish whatís causing the ECU to deny startup.
Be very careful about dead cranking the engine for too long, itís possible to flood the exhaust to the point where the back pressure becomes problematic and in the very worst case raw water can reach the exhaust manifold. Just close the raw water intake till she fires up.
Dirty fuel is really really bad for common rail engines in ways far beyond whatís bad for mechanically injected old style fuel systems, the pressures and tolerances far exceed those in traditional injection systems.
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Old 05-07-2022, 17:03   #6
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Re: Help Yanmar 4by3 wonít start

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Originally Posted by skipperpete View Post
This is a common rail computer controlled engine not the familiar mechanical pump and injectors so the problems are bit harder to solve. Certainly the primary fuel supply should be carefully inspected and tested for air leaks and restrictions but if this all checks out and you have an air free supply of clean fuel the diagnosis becomes a bit more difficult because it is very possible that one of the sensors is the culprit, sometimes itís one of the two on the actual common rail but you really need to access the error codes to establish whatís causing the ECU to deny startup.
Good info. I'm not familiar with the 4VY3 and didn't realize it was ECU controlled.

One thing though - I didn't see mention of filters beyond the primary/water separator - Does the 4BY3 not have a secondary filter? I'd think that if the fuel was bad enough to warrant changing the primary, then a secondary would also need a change, as well as an air bleed after both.
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Old 05-07-2022, 18:28   #7
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Re: Help Yanmar 4by3 wonít start

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Originally Posted by Pau Hana Daz View Post
Good info. I'm not familiar with the 4VY3 and didn't realize it was ECU controlled.



One thing though - I didn't see mention of filters beyond the primary/water separator - Does the 4BY3 not have a secondary filter? I'd think that if the fuel was bad enough to warrant changing the primary, then a secondary would also need a change, as well as an air bleed after both.


Youíre right, no mention of the secondary filter, there is an engine mounted filter with an optional sediment bowl and alarm sensor shown in the parts manual. After an incident with contaminated fuel it would be prudent to change all the filters...... on both engines.
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Old 05-07-2022, 23:03   #8
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Re: Help Yanmar 4by3 wonít start

If you need a full list of error codes look up a 2020 CF thread re ďYanmar 4BY3 alarmsĒ they are all listed there.
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Old 06-07-2022, 10:37   #9
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Re: Help Yanmar 4by3 wonít start

Both filters changed and took it apart all the way to pulling out injectors.

I have fuel from the low pressure pump but not getting to the rail from high injection pump.

Unfortunately I’m not in a place that I can find diagnostics. The only help I have is the dude that maintains the generator used for the island.

Do you know if unplugging a bad sensor will allow it to start?
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Old 06-07-2022, 16:01   #10
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Re: Help Yanmar 4by3 wonít start

No HP fuel flow is a little more complex because there should at least be bypass fuel happening but check the easy stuff first, sticky neutral switch on shift control is a definite candidate. There is still a chance thereís an airlock somewhere and regarding sensors, your best shot here is to swap them one at a time from the happy engine but remember to be really careful with the manifold ones, itís really high pressure fuel there and can be dangerous.
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Old 07-07-2022, 05:40   #11
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Re: Help Yanmar 4by3 wonít start

I have a 4BY2for Yanmar 2011. The issue I’ve had was a burned relay in the ECM black box attached to the engine. It controls the high-pressure fuel pump. When the ignition is turned on, before you crank, you should be able to hear and feel the fuel pump. NAPA carries the fuel relay, just get the correct number. There is a Yanmar dealer in Nassau, and if push comes to shove he will fly to where the boat is. If you do have a code reader you need to have an adapter that plugs in to the black box which is only available from Yanmar.
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Old 07-07-2022, 06:14   #12
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Re: Help Yanmar 4by3 wonít start

Disconnect your fuel line at the tank-side of your racor filter and purge it with an air compressor. You could have a clogged fuel pickup down at the bottom of your fuel tank and the compressed air will blow it out.
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Old 07-07-2022, 08:15   #13
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Re: Help Yanmar 4by3 wonít start

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Originally Posted by RobD527 View Post
Cruising along and it just died. Water separator had bad fuel in it so I changed it and the big primary fuel filter. Still wonít start. No engine alarms.

It cranks fine, all fluids are good, oil pressure gauge reads while cranking. I cracked big nut on top of large primary filter and fuel comes out.

Any ideas? Fuel relay? I found some relays in the black ecu box but not sure which one is fuel?

Iím am south of crooked island cruising on one engine heading to crooked island marina hoping they have services there
Hi Your problem started after an engine stall due to clogged filters
bleeding the fuel lines is the cure and get a wrench to fit!
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