To the mat! Is it really going full-throttle?

Often a problem such as a lack of power with an engine has the fix elude us. We are all guilty of looking for a complex cause instead of a simple solution.

The key to maximum power is the ability of the throttle to achieve its full range of travel. Makes sense, right?

Well, when was the last time you checked all your engines for the ability to give it all that it has? Don’t lie… probably never!

Small, large, gas, or diesel is all the same.

Every engine has the means to operate the throttle. With a carburetor, it will be the throttle plate that is opening. At the same time, a fuel-injected engine will have a throttle-body and diesel, the injection pump.

If the throttle cannot achieve full motion, the engine will never produce maximum power.

Checking the throttle movement is quite simple, but it will require two people, one to move the throttle and the other to confirm the action.

With the engine off, have your helper fully open the throttle and see if the throttle-body, carburetor or injection pump is going to its stop. To confirm this, gently take hold of the connection and test if you can obtain more travel. If you can, there is an issue.

The most common cause for lack of range for an application with a carb and throttle pedal is a mat or rug bunching up under the pedal. Look there first.

Another area to check is for a stretched cable from the throttle to the engine. Over time from use and thermal cycling, the cable will grow and give-up movement.

Any part of the throttle control system that swings in an arc will also lose range if the pivot point is worn and lateral movement is induced instead of an arc. This could be the pedal assembly or on a small engine, the control on the handle. If you work with your helper and study the movement, you will quickly see where the deflection is.

Keep in mind that when an engine loses full control of the throttle it is not only the maximum power that is diminished, but the part-throttle performance too.

The degradation is linear across the range of operation. Thus, as you command movement, the angle of rotation is less than desired. You think you are inducing 1/3 throttle, but it is only moving ¼ of the range.

Look, Ma, no cable!

In the last few years, the reliable but straightforward throttle cable has been replaced with a system called drive-by-wire.

With this an electric motor is connected to the throttle butterfly and is controlled by a series of sensors under the throttle pedal.

When the throttle is operated there are two sensors that work on a five-volt signal, each with the reverse output. This redundancy is employed as a safety factor.

The two sensor output voltages are compared by the engine control unit (ECU). It then sends a signal to the electric motor on the throttle plate and moves it to the required amount based on an advanced algorithm.

Much engineering time was invested in making the throttle feel “normal” to the driver as a cable would.

Though this system is not yet employed to any real extent on agricultural equipment, your family car and any gas or diesel-powered light-duty farm truck use it. Just pop the hood and look at the throttle body to see the small rotary motor.

If a drive-by-wire engine suddenly loses all power, the rotary motor or its electrical connection is usually the problem.

On a farm truck, keep in mind that dirt under the accelerator pedal can impact the sensors there and cause the same result. 

Please do not write off an engine as getting old and lazy. There is an excellent chance the throttle movement is limited, and there are still more horses under the hood than you think!