2012 22.2 Ask Albert!
Dear Albert,
My diesel tractor is getting hard to start with cooler weather. I crank for a long time and then when it starts, there are clouds of smoke. What’s the matter and how do I remedy it?
Thanks,
Smoky Tractor
Dear Smoky Tractor,
I have two initial questions: what kind (make and model) of tractor is it and what color is the smoke? Without more specifics, I will cover some basic issues related to your situation.
The main difference between gas and diesel is that gas has spark plugs that ignite the fuel in cylinders and diesel ignites the fuel by heat of compression. Most gas motors are 7:1 to 9:1 ratio of compression, which is the amount of volume in a cylinder when the piston is Bottom Dead Center (BDC) compared to the volume at Top Dead Center (TDC). On a diesel engine, the ratios start at 17:1 and go as high as 25:1. When the air is compressed to a higher degree, it creates heat. On a diesel motor, instead of a carburetor that mixes air and fuel before the combustion chamber, only air goes through the intake passage into the combustion chamber.
Most diesels have an injector pump that delivers very high-pressure fuel at a specified degree rotation before TDC through an injector. When the fuel is injected, it is done at such a high pressure that it atomizes into a fine mist, mixing with the heated air in the combustion chamber and igniting. Therefore, the critical components of ease of starting and optimal power on a diesel engine are:
- Specified compression (for any particular motor)
- Injector pump with proper injection timing and pressure
- Injector that is not worn, allowing it to create a fine enough mist or atomize the fuel properly
A starter that cranks the engine at a fast enough RPM to create the needed compression is also important for turning over a diesel motor.
Common issues
- Ambient air temperature. The colder the external temperature is, the more heat will need to be created for the fuel to combust. Cold temperatures also make the oil cold, slowing the engine’s ability to turn over. (A good battery may have enough juice to do this.) Additionally, the diesel fuel can become viscous. Adding diesel fuel conditioner or kerosene to the tank will keep the diesel from jelling (approximately one quart of kerosene for ten gallons of diesel fuel).
- Glow plugs. Most newer diesel engines have electrically operated wire resister glow plugs that pre-heat the air entering the cylinders to compensate for cold weather. Some of these have a single heating element in the intake manifold that preheats the air as the engine rotates/is cranked to start. Others have small heating electrodes that protrude directly into the combustion chamber. Usually the heating element burns out after a number of years, especially if they get worked hard. The glow plugs can be tested with a multimeter to see if they have resistance. See your shop manual for specified resistances.
- Air in fuel line. A common problem is that the fuel line is sucking air. Air can be sucked into the fuel system through the portion of the fuel line between the tank and the fuel transfer pump. This happens because air moves in easier than the fuel. As a result, the fuel won’t move up into the pump or air moves into the injector pump, making it difficult to start.Air compresses – liquids don’t. In order to obtain the high pressure for the injector pumps to operate the injectors (10,000 PSI or more), there can be no air in the system. The amount of fuel in the injector is so small, that it can’t open the poppet valve at the end of the injector to inject the fuel into the chamber if air is in the pump or injector lines.
- Plugged fuel filters.The fuel filters are in line between the tank and the injector pump on most diesels. Replace the filters if you’re having problems with the engine starting, running rough, or lacking power. Remember to fill the filters with fuel prior to installing.Most tractors have a manual pump lever on the transfer pump or a separate hand pump to prime or purge the fuel system. After changing the filter(s), look for the bleeder valve on top of the injector pump. Using a hand pump, pump until all the air bubbles stop coming out. If air bubbles continue, then air is being sucked in somewhere in the line and that is likely the problem.
- Air filter clogged. If at starting, the tractor motor runs but there is a lot of black smoke, check the air filter to make sure it’s clean and not obstructed. (This is also applicable to a gas motor.)
If the external temperature falls below forty degrees at night, an engine block heater will be most effective in warming a diesel engine for easy starting. The engine block heater raises the internal temperature, keeping oil and fuel flowing well despite cold weather.
Other smoke indicators
The color of smoke coming out of the exhaust is indicative of engine health. This is why I asked my initial question about the color of the smoke, Smoky Tractor.
- Blue, hazy smoke that smells like oil generally indicates a mechanical issue. Possible issues are worn valve guides, piston rings, or broken turbocharger seals.
- White smoke that smells like diesel indicates overfueling. This could mean the injector pump timing is late, the injector pump settings are not accurate, or the injectors are faulty. Injectors may be worn or, if a mechanical injector such as on some Cummins or Detroits, the timing or the stroke length could be off. Additionally, the turbo boost may not be working or may be out of adjustment.
- White smoke with a heavy smell of diesel in the smoke after or initial hard starting may indicate worn injectors. If the crankcase oil starts to smell like diesel and gets thin, the injectors are leaking, and the poppet valve is not seating correctly (or is worn out) and needs replacing or rebuilding.
Good diesel shops have injector testers that check for pressure and volumes of each injector. Shops are also able to test engine compression. Note that with most diesel engines, compression tests are more accurate when done while the motor is running. Each type of engine has its own adapter and procedure to test compression. Generally, compression gauges need to read at least 500 pounds.
In conclusion
In most cases of diesel engine starting issues, the engine fuel system is gummed-up with varnish. A good place to begin trouble shooting is to add fuel conditioner to a full tank of fuel and run the tractor for at least four hours straight. If that doesn’t address the starting issue, check the timing. Additional websites www.dieselbombers.com; www.auto.howstuffworks.com; www.firstdiesel.com.
Good luck and warmer weather is on the way,
Albert
