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Troubleshooting Your Yanmar Tractor Engine

Yanmar diesel tractor engines need Air, Fuel, and Compression to run.

Here are four troubleshooting tips to follow if you find that your Yanmar heavy-duty engine will not start OR starts and dies.

Tip #1: Inspect Air Cleaner

You must inspect your air cleaner to make sure it is free of debris.

Mice tend to build nests in the intake. Then they get sucked into the filter when you try to start the engine.

Simply remove the filter cover. Check for debris. Look for tiny mice with windblown fur that could be plugging the filter.

You should also remove the muffler. Air needs to get into the engine and it also needs to get out. In many instances, the internal baffles of the mufflers have fallen apart and blocked the exhaust. This could keep your engine from starting.

Tip #2: Test Fuel Injectors

You do not need to remove them completely. Simply loosen them several turns. Then, crank over the engine. Make sure the throttle is in the “run” or “full” throttle position. Look for small squirts of fuel coming out of each of the lines. You are not looking for a lot of fuel; roughly a ½ teaspoon.

An alternate way to test your injectors is by removing them from the engine. Then hook them back up to the steel fuel lines. Crank the engine over at full throttle. Let the injectors spray onto a piece of cardboard.

NOTE: The fuel will spray at a super-high pressure. It will easily cut through your skin and inject you with diesel. You are looking for a nice even cone mist (not a squirt, stream, or drips). If you see an even mist, then fuel is not likely your problem.

If you do NOT see an even mist...

Check to see if you are getting a good steady stream of fuel going into the injection pump. You can test this. Disconnect the fuel hose where it attaches to the injection pump. Be sure you have a good flow of fuel. Make sure it does not taper off after a few seconds. Let the fuel run out of the hose long enough to fill a quart bottle. Make sure you are not getting a “rush” of fuel that turns to a dribble after a few seconds.

If you are not getting a “rush” …

Work your way upstream. Inspect everything all the way up to the fuel tank. Eventually, you will find a place where there is a steady flow of fuel on one side of an item or hose and not on the other. Fuel going into a filter but not out. Once you find that --- then you have identified your problem.

Tip #3: Check for Low Compression

There is a super high amount of compression which detonates the diesel, causing an explosion (the main ingredient to the ”Yammer-Hammer”).

The key to getting the explosion is compression.

You may experience compression issues if the engine…

  • Was started with ether

  • Ran low on oil

  • Overheated

  • Has 10,000+ hours on it

  • Ran with a dirty or missing air cleaner

Low compression has been linked to improperly sealed piston rings, bad or stuck valves, a blown head gasket, or several other problems.

Compression needs to be checked with a Diesel compression tester.

A good Yanmar diesel engine can have close to 600psi. A diesel with around 400psi will be difficult to start. The engine needs to turn over quickly to build up that much compression. A low battery or a weak starter could result in the engine not spinning fast enough to start.

If it is cold outside you will need to use your glow plug (thermostart) to help the engine start since warm air is easier to ignite.

Tip #4: Check the Spark Timing

The spark (because of compression) must come at the correct time, so the engine will run.

The good news is that Yanmar tractor diesel engines do NOT get “out of time” unless you have…

  • Removed the front of the engine and did not correctly put the gears back in place.

  • Removed the injection pump and forgot to put the shims back under.

Both are unlikely but occasionally happen.

NOTE: Most of the "F" series and some of the “20” series have an electric fuel shutoff. This means you turn the key to the “off” position to kill the engine without having to pull a cable.

This electric shutoff is diagnosed separately to ensure it is working.

Please keep in mind that this is a basic troubleshooting list. There are other problems that can occur.

As always there is the risk of injury while performing these tests. If you do not feel that you can perform these tests --- do not attempt them.

If you need any further help or have any questions about tractors or anything else, please contact your dealer, local mechanic, or call us at 602-734-9944. Please ask about our current new and used tractor supply.

Team Tractor and Equipment - #1 Tractor Dealer in Arizona. We sell and service most major brands of tractors including Yanmar, Kubota, John Deere, TYM, Mahindra, Kioti, Case, New Holland, Massey Ferguson, Ford, Deutz, Case IH, Farmall, International Harvester, Branson Tractors, LS, Shibura, Claas Tractor, McCormick Tractors, Valtra, Solis, YTO, Montana, and Nortrac.

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Ron Johnson
Ron Johnson

I have a John Deere 455 with the Yanmar engine. While mowing it seemed like it was running out of fuel but when I disengaged the mower it would catch up and start running better. It got worse the more I used it. It finally died and now will not run. It cranks over fine and tries to run but then dies. I've replaced the fuel filter and fuel pump. Could this be an ignition switch issue?


Todd Wood
Todd Wood

my tractor is flashing error and runs at about half throttle. how do i fix this

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