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Tractor Runs But Has No Power (Gas & Diesel Engine Issues)

Tractor Runs But Has No Power (Gas & Diesel Engine Issues)

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Paul Brown

Tractor engine issues can be expensive. Look through this guide before calling in a pricey professional to see if you can determine the cause.

If your tractor runs but has no power, it is most likely that it is starved for fuel. To fix this, check and replace your fuel filter, bleed your fuel lines, and check all fuel connections. 

This is one of the most common issues when dealing with diesel engines. To learn more about how to fix your tractor, whether it is a gas or diesel engine, read on.

Understanding The Differences Between Gas and Diesel Engines

To begin, let’s look at the basic differences between gas and diesel engines. This will show us that we may have different reasons for losing power with each type of engine.

Both engines work in a series of four actions that, together, create the combustion needed to make fuel engines go.


This is the first step in the combustion process. In a gas engine, air and fuel are let into the cylinders. Only air is let in at this point in a diesel engine, with fuel being introduced later.


Before ignition can happen, the contents of the cylinders must be heated up to create pressure. Because a gas engine’s cylinders contain air and fuel, the compression must happen at a lower temperature or risk self-ignition. 

In a diesel engine, only air is in the cylinders at this time, so the compression can happen at a much higher temperature. For the next step, it is crucial for the cylinders to reach a temperature of self-ignition.


One of the main differences between the two types of engines is the way they ignite. Because the gas engines compress at a lower temperature, they need an external spark to ignite the gas. Enter, the spark plug.

In a diesel engine, the cylinders and air inside are compressed at such a high heat that the fuel needs simply to be injected into the cylinders, and the fuel will self-ignite (source).


This is the only step that is identical for the two engines. The combustion process creates fumes, which are let out through the engine’s exhaust. 

This entire process is repeated many times a second to keep the engine running.

Because a diesel engine ignites through injecting its fuel into a high-temperature chamber, it has no need for spark plugs.

It also doesn’t need a carburetor, which, in a gas engine, serves to pre-mix the air and fuel before it is injected into the cylinders.

Most Common Issues for Lack of Power in a Gas Tractor Engine

The most common issues for when your gas tractor runs but has no power include:

  • Air filter: If your air filter is clogged or extremely dirty, it can block air intake for the engine. Looking at how gas engines work, we can see that air is crucial for the engine to create power.

    Your tractor may still run if it has a dirty air filter but may lack the power it normally has. To fix this, remove and replace the air filter.
  • Carburetor: Carburetors are one of the downfalls of having a gas engine. They are an extra piece that often cost large amounts to diagnose and fix.

    If your carburetor is old, dirty, or rusted, this can cause your tractor to lose power. You should also check the choke on your carburetor if it is partially closed, it will disrupt the engine’s air intake and cause it to lose power.
  • Old fluids: Another main cause of lack of power in a gas engine is the presence of expired fluids. Gas that has been left to sit in the tank will attract water, due to the quantity of ethanol in the gas.

    Ethanol attracts water, which can cause your engine to weaken, or quit starting altogether.
  • Blocked exhaust: Check your exhaust pipe to make sure there are no blockages or collapses. A blocked exhaust pipe can limit the air output, therefore limiting the potential power of the engine (source).

What Causes A Diesel Engine To Lose Power?

If your tractor starts up and runs but has no power when in use, one of the first places to check is the fuel system.

The most common causes of a diesel tractor that runs but has no power include:

  • Bad Fuel
  • Fuel system vacuum
  • Restricted fuel flow
  • Restricted air intake

In each case, the diesel engine is not getting the optimum amount of fuel or air needed for efficient combustion.

Let’s look at each these one by one:

  • Old fuel: Just like with gas engines, old diesel can cause engine issues. Diesel does have a shelf life (source). Old diesel can develop sludge-like traits, causing your motor to be “bogged” down by the fuel.

    The main contaminants of diesel are water, heat, bacteria, and fungi, and contact with zinc or copper.
  • Fuel system vacuum: Another common issue that makes many problems for tractor owners is the creation of a vacuum in the fuel tank. Luckily, this is one of the easiest fixes.

    A simple way to troubleshoot this that many farmers use is to loosen or remove the fuel tank cap and run your tractor like that for some time. If your tractor works like usual, you’ll know the fuel tank cap is the culprit. Replace the cap and carry on.

    Note: Running a tractor with the fuel cap off is not my favorite recommendation. You risk getting dirt into the tank. I prefer to give clean the cap well and try it this way first. Many times a good cleaning will remove any debris that is clogging up the venting system in the cap.
  • Restricted fuel flow: One of the most common issues in a diesel engine misbehaving is the engine’s lack of fuel. Check your fuel filters, your lift pumps, and your fuel lines.

    If your fuel lines have any amount of air in them, your engine will not get fuel delivered to it at the proper rate and it may quit running altogether.

    To fix air-filled fuel lines, you must bleed the lines, sending fuel through them when disconnected to replace all air pockets.
  • Restricted air intake: As we know, air is crucial for the operation of internal combustion engines. If your diesel engine has restricted air intake, it can lose power.

    Check the air filter for blockages and debris, and ensure it is installed properly.

Other Reasons Your Tractor Might be Losing Power

If you’ve taken your tractor through the criteria above and you still find that it is running but losing power, there are a few more reasons it may be doing so.

  1. Your brakes may not be fully disengaging. This will create drag and diminish power.
  2. You are trying to haul too heavy of a load. If your engine is overworked, it may lose power.
  3. Injector issues. Your fuel injector, in a diesel, may be injecting too much or too little fuel. It could also be stuck in an open position, and not injecting the fuel properly.
  4. Mechanical failure. In either type of engine, there is always the risk of something simply breaking. A cracked valve or chamber can leak pressure and lower the power output of your engine.

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When to Call a Professional

If none of the areas above reveal simple solutions to your engine issues, then it’s important to bring in a professional. Working on heavy machinery is risky. Not only could you damage the expensive machine, but you could also cause extreme harm to yourself.


There are many different reasons why your tractor may be running, but lacking power. The most common of these include:

  • Blocked air intakes
  • Carburetor issues
  • Old fluids including fuel and oil
  • Lack of fuel in the engine
  • Fuel tank creating a vacuum
  • Brakes not fully disengaging
  • Overloading the engine
  • Fuel injector issues
  • Mechanical failures

The best place to start is with the external parts of the machine. Check the air intakes for blockages, and the fuel cap and air filters for dirt and debris.

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