Yanmar Trouble Shooting Tips

 

Engine

Won't Start Or Starts Then Dies

Note: There are a few Yanmar tractors including most of the "F" series and a few of the '20 series that have an electric fuel shutoff (turning the key to the off position kills the engine instead of having to pull a cable). This electric shutoff will need to be diagnosed separately to be sure it is working.

These little Yanmar diesel engines are very simple. They only need 3 things to run: Fuel, Spark (in the form of compression), and Air. The following is arranged from easiest to check to most difficult to check.

Air
Inspect your air cleaner to be sure it is not clogged. It is not uncommon for mice to build nests in the intake and get sucked into the filter when you try to start. Remove the filter cover and look for debris or tiny mice with windblown fur plugging the filter. It might also be a good idea to remove the muffler. Air needs to get into the engine but it also needs to get out. We have seen several cases where the internal baffles of the mufflers have fallen apart and blocked the exhaust enough to keep the tractor from starting.

Fuel
Loosen all of the steel fuel lines where they are attached to the injectors. You don't necessarily need to remove them completely but loosen them several turns. Crank over the engine (with the throttle in the 'run' or full throttle position) and see if you can see small squirts of fuel coming out of each of the lines. You are not looking for a lot of fuel here. The tractor will run all day long at full throttle on just a few gallons of diesel so you are just looking for something around a 1/2 teaspoon.

You can also test your injectors by removing them from the engine and hooking them back up to the steel fuel lines. Crank the engine over at full throttle and let them spray onto a piece of cardboard. ** DANGER! The fuel sprays at a super high pressure. It will easily cut right through your skin & inject you with diesel (FYI... That is bad). You are looking for a nice even cone mist (not a squirt or stream or drips).

If yes, then fuel is not likely your problem.

If no...

Check to be sure you are getting a good steady stream of fuel going into the injection pump. The easiest way to test this is to disconnect the fuel hose where it attaches to the injection pump. You want to be sure that you have a good flow of fuel and be sure that it does not taper off after a few seconds. It is best to let the fuel run out of the hose long enough to fill a quart bottle just to be sure you are not getting a 'gush' of fuel which then turns to a dribble after a few seconds.

If no..

Work your way up stream inspecting everything all the way up until you end up at the fuel tank. You will eventually 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, for example. Once you find that then you have found your problem.

 

Spark
There is no spark plug on a diesel but there is a super high amount of compression which detonates the diesel and causes an explosion (the main ingredient to the 'Yammer-Hammer'). The key to getting the explosion is compression. If the engine has been overheated, ever started with ether, has many thousand (10,000+) hours on it, ran with a dirty or missing air cleaner, or ran low on oil- you could possibly have low compression. Low compression can be due to piston rings that are not sealing correctly, a blown head gasket, bad or stuck valves, or a number of other problems. Compression will need to be checked with a diesel compression tester (gasoline compression testers do not read high enough pressures). A good Yanmar diesel engine can have close to 600psi. A Yanmar diesel with around 400psi will become very hard to start. Keep in mind that the engine will need to turn over quickly in order to build that much compression. If you have a low battery or a weak starter you might not be able to get the engine spinning fast enough to start. If it is cold outside you will also need to use your glow plug (thermostart) to help the engine start since warm air is easier to ignite.

Timing.
Ok.. for those of you keeping count this is technically a 4th item but timing is really in the 'spark' category. This is because the spark must come at the correct time or the engine will not run. Fortunately, Yanmar diesels do not get 'out of time' unless you have either 1)- removed the injection pump & forgot to put the shims back under it or 2)- have removed the front of the engine and did not get the gears back in the right spot. Both are pretty unlikely.

 

This is a basic troubleshooting list. Of course, there are other problems that are less like to happen but can occur. It was impossible to include all of the possible problems in this article but the things listed above account for over 90% of our tech support calls. If you do not feel like you have the ability to do these test then please contact a local mechanic or give us a call. As with pretty much anything in life... there is the risk of injury doing some of these tests.