Testing A Yanmar Tractor Fuel Injector

The easiest (and cheapest) way to test a Yanmar tractor fuel injector is by using the injector itself. 

First (if the engine will run) while the engine is running at an idle- loosen the steel injection lines on each injector one at a time. You should notice a significant change in the engine sound each time you loosen an injector's line. The engine should get noticeably rougher or lose a noticeable amount of power each time you loosen the fuel line because, by loosening the line, you are essentially de-activating that cylinder. If you can loosen a line and there is no change to the sound of the engine then that cylinder was not firing for some reason. Cutting the fuel to that cylinder didn't change anything because it was not running in the first place. It could be a bad injector, bad injection pump, or even damage to that cylinder causing compression to be so low that it can not ignite the fuel. 

** WARNING! The fuel injection system is under thousands of pounds of pressure. The fuel coming out of the injectors can very easily pierce your skin and cause serious or fatal injuries. People often joke that they have diesel running through their veins but, in the real world, diesel in your blood is not compatible with life. Do not let the highly pressurized fuel come in contact with any part of you. 

To test the injectors:

• Unscrew the steel lines from your your injectors
• Remove the injectors from the engine
• Loosen the injection lines from the injection pump so that you can re-position the lines & injectors.
• Hook injectors back up to the steel lines with the injectors pointing away from the engine
• Make sure throttle is in the full speed position.
• Make sure tractor & PTO are in neutral 
• Crank the engine over and let the injectors spray onto a piece of cardboard
• Check for the proper pattern below. You are looking for a nice conical mist pattern on the cardboard. It does not have to be perfect but, the better the pattern, the better the engine will run. Diesel engines do require a fine mist in order to burn. If you are getting a 'squirt' or 'stream' then that fuel may not be burning in the combustion cycle. 
• If you find an injector that is not spraying correctly, swap it with a different injection line in order to be sure it is not a problem with the injection pump. If the problem follows the injector then the injector needs serviced. If the problem stays with the cylinder then it might be a problem with the injection pump.

If the injectors test ok then compression might be the problem and you might consider doing a compression test using our compression tester kit.