Yanmar 20GM20 starts but wont run

[mowerandy]

This on behalf of a friend with some engine trouble. Any input will be much appreciated (he's on his home berth so no emergency here).
We couldn't start his 2GM20 Yanmar yesterday. Cranks and starts normally but dies within 2-5 seconds. Disconnected throttle linkage to give it a bit, without engaging the gearbox, but doesn't help. If anything throttle seems to kill it a fraction faster.
I checked the fuel supply to the injector pump and it looks like plenty of good clean diesel coming through to the pump.
My friend, who was there before me, reported some white smoke when trying earlier.
I tried it on Aerostart and it cranked up to slightly higher rpm before dying again.

Anyone experienced this before? What diagnostic steps would you recommend next? I am no diesel mechanic, but was thinking to have the injectors out to check the high pressure spray pattern/look for blockages. I guess it would make sense to compression test it while the injectors are out, but am thinking it wouldn't start in the first place (without ether) if the compression was suddenly lost (and it was running fine last outing a week ago). For that matter it wouldn't start if the injectors had a problem either. But it seems very happy when it first starts, but then just loses rpm and stalls within a few seconds.
Maybe rather than pulling the injectors, I should take off the high pressure lines to the injectors and check the flow there (which is easier).
I'm thinking that the injector pump might be at fault, and guessing that is not good news...

[a64pilot]

If you are certain it’s getting fuel, bleed it well, many times a Diesel with air in the system will start and then die.
What is Aerostart? If it’s Ether, then forego that, it can cause harm unless your schooled in its use, and it’s a starting aid anyway, your starting, but dieing after the start, due I’m sure to fuel starvation.
If it were a generator or another motor equipped with Murphy switches, then I’d suspect low oil pressure and or bad switch, but I assume this is a propulsion engine and has no Murphy switches?

[Ruffriders]

Yep, fuel or air, simple but sometimes complicated

[gamayun]

Originally Posted by Ruffriders

Yep, fuel or air, simple but sometimes complicated

I'm a newbie too, but fuel or air are what the experts in the shop say. Check the simplest things first like whether it's getting fuel (bleed well) or if the exhaust elbow is blocked. Check injectors next. A good book to get is, Trouble Shooting Marine Diesels by Peter Compton. For white smoke, it could be water in the fuel/contaminated fuel, but it also says, "If your engine suffers from poor staring, erratic rpm, or excessive exhaust smoke, your problems are more likely due to defective injectors than to all other causes combined." This is what I think my problem is because it's hard to start and there's a lot of white smoke before it gets warmed up.

[Lepke]

White smoke is steam or unburnt diesel. Rings are designed to expand with combustion pressure. Making a tight seal. Using too much ether will cause extreme pressure, braking the rings. Then you need ether all the time and burn oil, use more fuel, etc.
You have a fuel problem or a restricted air intake or exhaust. As recommended above, the exhaust elbow clogged with rust is common. And once I found a dead aquatic animal stuck in the wet exhaust.

[jimbunyard]

More information would be helpful. Definitely don't start tearing things apart before doing some simple tests.

Did the problem start all at once, or did your friend notice anything odd beforehand? Has he recently changed the filters or been in rough weather?

As is the consensus, it sounds fuel related. Check for air in the system, for air getting sucked into the system from old, dryed out or cracked hoses, or sealing rings on filters. A small leak may not be obvious; if on the vacuum side it will be especially hard to find.

There could also be a screen in the bottom of the pickup tube in the fuel tank that is getting intermittently clogged (though the cutoff time from start to dying seems rather short), if there is, remove it. Mud wasps and dirt daubers have a habit of clogging fuel tank vents, which can also cause similar problems...

The lift pump could have iffy valves.

Does the engine have a decompression lever(s)? Is it (are they) fully closed?

Sometimes you can isolate fuel problems by running the engine out of a jug with a short length of hose...

[NYSail]

Make sure with all this attempted starting you don’t flood the engine........

Also sounds like fuel / air starvation.

Good luck

[Ruffriders]

Take off fuel line and make sure you have fuel there first then Crack each injector line and make sure fuel is coming out at the injectors and it is clear (not milky)
Check air filter, should be clean and dry.
I had the same problem when I installed a new engine, I had to put an electric booster pump on line as I didn’t have enough fuel pressure.

[NYSail]

Maybe bad fuel? This happen out of the blue??

[Ruffriders]

Raycors

[Mike Banks]

Starts but stops when you let go of the starter key?

Hold-in relay windings at the pump are disconnected or kaput.

[Cheechako]

Check the fuel filters. You should bleed it very well at the injectors until no bubbles at all.... but if it wont run that is hard. You can install an in line electric fuel pump before the filters for this. Or you can have someone crank the engine , may 20 seconds then rest the starter. Watch out you dont fill up the muffler with water though!
If it starts it's not compression. Even if the compression is bad it should continue to run if it starts up.

[wcapman]

Fuel and Air.
Assuming there is nothing wrong with the fuel supply, look at the exhaust. If the engine runs for 4 or 5 sec and dies, there may be a blockage in the exhaust. As the exhaust tries to exit the system it can't, so it builds up backpressure, choking the engine. A partial blockage will bleed down in a few seconds of no engine running, so the cycle will repeat.

The fact that the engine dies more quickly when power is applied is a clue that you aren't getting the exhaust out.

The first thing to suspect is the exhaust riser/mixing elbow. Remove it and check for blockage due to rust. The area after the water injector is the usual culprit. If no problem is found there, move on to the hydrolift muffler. These can build up deposits in the bottom and block the lift passage. The engine chokes on back pressure in either case. Remove it and shake it out or replace it. If the mixing El is blocked, chances are good that there is a buildup of rust in the muffler, too. Clean them both out to restore full power.

Critters can sometime climb into the exhaust hose at its exit and die in there. Check that there is no blockage in the exhaust hose if none is found elsewhere.

A good starting "fluid" to use, especially in cold weather, is WD-40. Spray just a little in the intake. It will not damage a diesel like starting fluids for gasoline engines will.

[Cheechako]

Originally Posted by wcapman

Fuel and Air.
Assuming there is nothing wrong with the fuel supply, look at the exhaust. If the engine runs for 4 or 5 sec and dies, there may be a blockage in the exhaust. As the exhaust tries to exit the system it can't, so it builds up backpressure, choking the engine. A partial blockage will bleed down in a few seconds of no engine running, so the cycle will repeat.

The fact that the engine dies more quickly when power is applied is a clue that you aren't getting the exhaust out.

The first thing to suspect is the exhaust riser/mixing elbow. Remove it and check for blockage due to rust. The area after the water injector is the usual culprit. If no problem is found there, move on to the hydrolift muffler. These can build up deposits in the bottom and block the lift passage. The engine chokes on back pressure in either case. Remove it and shake it out or replace it. If the mixing El is blocked, chances are good that there is a buildup of rust in the muffler, too. Clean them both out to restore full power.

Critters can sometime climb into the exhaust hose at its exit and die in there. Check that there is no blockage in the exhaust hose if none is found elsewhere.

A good starting "fluid" to use, especially in cold weather, is WD-40. Spray just a little in the intake. It will not damage a diesel like starting fluids for gasoline engines will.

Good point. Does any water come out the exhaust? If so, I doubt it would die in a few seconds from partial clogging though.

[Boatyarddog]

Originally Posted by wcapman

Fuel and Air.
Assuming there is nothing wrong with the fuel supply, look at the exhaust. If the engine runs for 4 or 5 sec and dies, there may be a blockage in the exhaust. As the exhaust tries to exit the system it can't, so it builds up backpressure, choking the engine. A partial blockage will bleed down in a few seconds of no engine running, so the cycle will repeat.

The fact that the engine dies more quickly when power is applied is a clue that you aren't getting the exhaust out.

The first thing to suspect is the exhaust riser/mixing elbow. Remove it and check for blockage due to rust. The area after the water injector is the usual culprit. If no problem is found there, move on to the hydrolift muffler. These can build up deposits in the bottom and block the lift passage. The engine chokes on back pressure in either case. Remove it and shake it out or replace it. If the mixing El is blocked, chances are good that there is a buildup of rust in the muffler, too. Clean them both out to restore full power.

Critters can sometime climb into the exhaust hose at its exit and die in there. Check that there is no blockage in the exhaust hose if none is found elsewhere.

A good starting "fluid" to use, especially in cold weather, is WD-40. Spray just a little in the intake. It will not damage a diesel like starting fluids for gasoline engines will.

Yes, first check the riser for a blockage, this is common, especially the elbow mixing type.
I'd remove the hose to the muffler and un bolt the riser from the head.
Try to start it this way.
Back pressure on the engine is relieved this way.
These engines use a lever to stop them, be sure it is fully forward, not applied.
Then if the lift pump for fuel is supplying fuel to the injection pump, you should see a good push of diesel if you operate the primer lever on the lift pump.
Remember, these engine have a primary fuel filter bolted to the engine, usually mounted in front, up high.
These often are forgotten when changing out fuel filters.
If your not seeing fuel at the lift pump hose to the injection pump, the filter may be dirty, or the pump is failing.
At that point you could attach an electric pump to the inflection pump, this eliminates the lift pump section, if it runs then.
Then you'll know.
Cheers
SV Cloud Duster