Post 8: The Role of Sensors in Fuel Delivery

If you haven’t started at the beginning, then you are missing some things in your education. Please go to Post 1 and start there NOW to be sure you get a thorough understanding.

There is more computing power in the average cell phone than what was used to take the Apollo 13 mission to the moon?


Instead of setting us free, the sad thing is when we buy these fuel consuming beasts, it actually works in the reverse. We become slaves. Slaves to those that program and design the systems that drive them down the road, for they are the ones that determine how much fuel it takes to move us to our destinations.

In the past 100 years, technology has advanced to a phenomenal degree. We allegedly have the most fuel efficient vehicles than have ever been made. While I believe this is true to a certain degree, it is also true these systems enable the Slave Masters to control what can and cannot be done to improve your fuel ECONOMY. And economy is not to be confused with efficiency.

The automotive industry considers the measure of the exhaust to be representative of a system’s efficiency, NOT the amount of fuel required to get the job done. But the public is programmed. Programmed to put their faith in the liars cheats and thieves that are running our world.

In the interest of taking some of our power back in one small area (how much fuel we use) we face a number of obstacles, the vast majority residing in the actions and limitations set forth in the programming of the ECU. Ignition Timing, Injector Pulse Width, Catalytic Converter Temperature, and many other aspects affect fuel economy are pre-set and immutable.

What we’re going to do today is to talk about the role of various sensors in the computer’s calculations that determine the amount of fuel to deliver while the engine is running. ALL of these systems must be considered in your quest for 100+.

I’m going to start with the air and move with it through the engine, considering the actions of each sensor start to finish. Then, we will consider what can be done with each to further enhance the results of The Gadgetman Groove.

Now, some of these will enhance a NON-Grooved engine, but they are to be used with caution on engines that are not vaporizing the fuel completely, for it is this wasted energy that we want to reclaim, enhancing not only Fuel Efficiency, but Fuel Economy as well.

It is this waste fuel that causes most of the wear in our engines, so reducing it will also enhance engine operation and life-span.

Study this diagram for insight into MAF sensor operations.

The first sensors the air encounters is the MAF and/or the IAT. The Mass-Air Flow sensor is a device that measures several dynamics. It measures both the amount of air passing over it, the temperature and even the relative humidity as it acts on a heated element (resistor) and uses the current flow through the circuit to determine the how much fuel should be delivered according to the amount of air, thereby managing the Air-Fuel Ratio. To get more technical data on the MAF, go to the Wikipedia article.

The Intake Air Temperature sensor does essentially the same thing, in essentially the same way (using a resistor) and is much simpler in construction as well as operation. Use the information from the Wiki article on the MAF to learn about its function.

From there, the air will be drawn through the throttle assembly. Here, the Throttle Position Sensor (TPS) has its role in the ECU’s functions. Using a variable resistor that is actuated by the throttle controls (whether cable or computer controlled throttle assemblies) the ECU can determine how much fuel should be delivered. It also uses this sensor to determine shift points in many vehicles.


The TPS is also a key component if you’re working on

fuel vaporization systems to determine vapor delivery rates.

Now, the air enters the intake manifold. Here, the air is presented to the MAP or Manifold-Absolute Pressure sensor. Again, turn to Wikipedia for good information.

This video explains in simple terms how the MAP sensor functions.

This sensor is designed to measure the difference between the pressure inside the intake Manifold and the outside or ‘Absolute’ pressure using (again) a variable resistor. Using the value presented to the ECU, the computer calculates the proper measure of fuel to deliver, once again referencing all the other sensors to confirm the proper AFR.

From here, the air enters the head, where the fuel is delivered to the air stream as it enters the combustion chamber. To determine ignition timing, the ECU utilizes both the Crankshaft or Camshaft Sensor and the Knock Sensor.

Here’s a short video on what the knock sensor does and how it does it:

There are more in-depth videos on YouTube if you want to look for them. Remember, knowledge is power. Actually, knowledge is only POTENTIAL power. If you don’t use it, it is not very powerful, now, is it?

Once the ECU has made it’s determination of proper ignition point, it will send the signal to to the ignition circuit commanding a spark be delivered.


Don’t use Motorcraft spark plugs!

Their design is defective, as is common with resistor-style plugs. When the internal resistor

burns out (they all do in time!) the anode of the resistor can fall into

the combustion chamber, necessitating engine rebuild.

This happened to us in Provo Utah. $4,000 in repairs and one week later,

We could finally continue our trip.

Ford/Motorcraft is facing class-action lawsuits because of this.

When the fuel in the combustion chamber is ignited, it is then pumped out to the exhaust manifold, where it is exposed to the Oxygen Sensor.

Here is a nice video by EricTheCarGuy on its operations. (I do so LOVE YouTube!)


The O2 Sensor compares the oxygen level in the exhaust with ambient air.

The method of measuring the external O2 content is unclear, but

it is known that grease and oil deposits on the OUTSIDE of the sensor and

sensor wires may cause erroneous readings.

This sensor is only read during ‘Closed Loop’ operations. During ‘Open Loop’ operations, fuel management is calculated based on all sensor activity, disregarding the oxygen content. This can be a pain in some systems as the engine operations in some systems drop into Open Loop whenever there is a change in engine speed.

Using the values determined by the Upstream O2 sensor, the ECU will alter the fuel trims to maintain proper AFR.

Now, the air is in the exhaust and the process should be complete, shouldn’t it? But it is most DEFINITELY NOT!

From the upstream O2 sensor, the exhaust gas passes down the pipes to the Catalytic Converter. Here is the most insidious aspect of the programming of the ECU fuel management systems. Using yet another oxygen sensor, they are able to manage catalytic converter function.

As the operating temperature of the Cat is closely controlled to maintain its catalytic function (they operate best at 900-1000 degrees F. (According tothis article) In order to maintain this temperature, the ECU will either decrease or increase fuel delivery, despite what the upstream O2 indicates. They do this by using the heater circuit, which will increase in resistance as the temperature increases

Here’s a video on how the ECU works with all its sensors, explaining the role of each. Perhaps it will enable you to find a new approach to the fuel efficiency puzzle. (26 mins)


Now, we’ve covered about all the sensors I can think of. At least, I’ve covered the ones of which I’m aware! Let’s move on to how they work together and (more importantly!) what can be done to effectively regain management of your own fuel delivery needs.

Post 1

Post 1-Basic Flows in a Gasoline Engine

Post 2-Intake Flows and Wave-Form Technology

Post 3-Improving the Vacuum System

Post 4-An Avearge Installation

Post 5-Varnish and Vacuum

Post 6-Hidden Weaknesses

Post 7-Diagnosing Error Codes

Post 9-Adjusting Your Spark Plug for Maximum Efficiency

2 Responses to Post 8: The Role of Sensors in Fuel Delivery

  1. divedaddy03 says:

    This is a very good post Ron. It really does help me to wrap my mind around all of the sensors and their functions!

  2. This is by far one of the most informative articles i've seen related to the mass air flow sensor and which codes they throw. I did NOT know that reducing the air flow levels too much could kill the MAF. I wish I would have known that 6 months ago, and it would have saved me some money.