Yanmar 2gm20f

[IndyBlue]

I just purchased a used Hunter 31 that has a 2GM20F engine. The engine had several fuel leaks (lift pump, injector pump seal) and also smoked very bad at 1/4 throttle and above.
After replacing the seals and lift pump, bleed system and added fresh fuel. Started engine after a couple of seconds engine RPM's go to WOT. Pulled inspection plate to insure that the rack on pump is not stuck. Moves good and seems to be operating normally.
Sent injectors and pump out to be rebuilt and reinstalled. Bleed system and same issue is still going on. Remove inspection plate and insure rack is moving freely with engine stop lever.
After further inspection found only one of the cylinders is the problem (remove fuel line to one cyl then the other). #1 cylinder idles normal #2 wide open.
Don't know where to go next. any help would be greatly appreciated.

Thanks for your help

[Compass790]

Welcome to the CF community,
Have you checked oil level & made sure you dont have diesel in oil?
I would also check the exhaust elbow, it wont affect your WOT problem but can cause the black smoke. Common for the elbows to clog up.

[IndyBlue]

While waiting on the pump to be rebuilt I changed the oil and filters including fuel. I also removed the mixing elbow and cleaned out (not clogged). There was no fuel in the oil.

[Compass790]

Originally Posted by IndyBlue

While waiting on the pump to be rebuilt I changed the oil and filters including fuel. I also removed the mixing elbow and cleaned out (not clogged). There was no fuel in the oil.

Almost sounds to me like injection pump may have been assembled incorrectly assuming the WOT on one cylinder problem only occurred after you installed the rebuilt pump.
You could try catching the diesel as its squirts out of each injection pipe turning over decompressed by hand & see if there is a volume difference. I've never tried this, its just an idea, imagine it would be a bit difficult as it squirts out fast.
That way you can find out if pump is assembled wrong.
Do you have the service manual? I believe there is one in the CF library.

Someone with specific 2GM20 experience may be able to help you better

[gonesail]

if the yanmar exhaust elbow has not been replaced within 600 hours you probably should plan on doing that. they make stainless steel versions now.

[Chayal]

Originally Posted by Compass790

Almost sounds to me like injection pump may have been assembled incorrectly assuming the WOT on one cylinder problem only occurred after you installed the rebuilt pump.
You could try catching the diesel as its squirts out of each injection pipe turning over decompressed by hand & see if there is a volume difference. I've never tried this, its just an idea, imagine it would be a bit difficult as it squirts out fast.
That way you can find out if pump is assembled wrong.
Do you have the service manual? I believe there is one in the CF library.

Someone with specific 2GM20 experience may be able to help you better

Not a bad idea at all ^

OP is at the mercy of the injection shop right now.

I wonder what they replaced specifically... it wouldn’t be the first time a pump or injector had to be resent back.

[Wotname]

Originally Posted by IndyBlue

I just purchased a used Hunter 31 that has a 2GM20F engine. The engine had several fuel leaks (lift pump, injector pump seal) and also smoked very bad at 1/4 throttle and above.
After replacing the seals and lift pump, bleed system and added fresh fuel. Started engine after a couple of seconds engine RPM's go to WOT. Pulled inspection plate to insure that the rack on pump is not stuck. Moves good and seems to be operating normally.
Sent injectors and pump out to be rebuilt and reinstalled. Bleed system and same issue is still going on. Remove inspection plate and insure rack is moving freely with engine stop lever.
After further inspection found only one of the cylinders is the problem (remove fuel line to one cyl then the other). #1 cylinder idles normal #2 wide open.
Don't know where to go next. any help would be greatly appreciated.

Thanks for your help

Welcome aboard CF, IndyB.

Let me see if I understandably this correctly.

The engine had some fuel leaks but otherwise ran correctly.
You replaced the lift pump.
You replaced some seals on the injector pump (IP).
Now the engine goes into WOT rpm after start up.

Conclusion - you did something wrong when you replaced the IP seals.

Now the IP has only got a couple of seals.
The O ring in the delivery valves on the top while the injector pipes are fitted at the high pressure side of the IP.
The banjo crush washers on the low pressure fuel inlet line.

Neither of these could cause you problem.

So did you in any way change or remove anything else with the IP (before you removed it for a rebuild).

It sounds like something has gone astray with the no load max rev limiter, the fuel injection limiter, the governor arm / rack connection or the regulator / governor arm connection. But none of these should have been touched (??).

[Wotname]

Found the following in the service manual which may help you.

Also my previous post should have read - The O ring in the delivery valves on the top where the injector pipes are fitted at the high pressure side of the IP.

[IndyBlue]

I read that in the owners manual prior to replacing seals. Torq set as outlined in owners manual. Plus sent pump out and did not tighten those when I install remand unit. Check rack after install through inspection access and rack is moving freely. Also check rack movement while engine running (what a mess) governor is moving rack with no resistance.

[Wotname]

Are all the springs as shown below in place (disregard the coloured circles)?

The governor should be holding the rack closed if the rpm increases with the regulator lever (throttle) in the idle position.
If the engine is running away with the rack closed then either the IP is faulty or the engine is getting fuel (oil etc) from another source (sump etc).

Do let us know when you get to the bottom of it.

[AA3JY]

Replaced the high pressure pump shims with the correct number(thickness)..?

[Compass790]

Originally Posted by IndyBlue

I read that in the owners manual prior to replacing seals. Torq set as outlined in owners manual. Plus sent pump out and did not tighten those when I install remand unit. Check rack after install through inspection access and rack is moving freely. Also check rack movement while engine running (what a mess) governor is moving rack with no resistance.

Blew a fair bit of oil out did it?
Still think you need to check if there are different volumes of diesel coming out the injection pipes & then you will know the assembly is wrong if the volumes are different.
My suspicion is one plunger rotation setting may be awry.
Timing shims wont make one cylinder wrong.
If they didnt put it on the pump tester after reassembly could have missed it.

[Wotname]

I'm still not entirely sure if the fault occurred initially before the IP rebuild or after it. I can read the OP both ways