Modern SensorsModern Engine Sensors
As I mentioned in the first post in this series, tuning a car when I was a teenager meant that you got out your timing light, a couple of hand tools and you asked your old man to show you how to loosen the distributor and you would twist it a bit, then make a turn or two on the carburetor. Unfortunately, everything on the modern engine is electronic and your old man can’t figure out how to use the TiVo. Electronics means computers. Computers need information. The car’s computer will get all the information from the multitude of sensors that litter your engine bay.

Modern engines use these electronic sensors to feed information into their “brains” or Engine Control Unit (ECU) and make calculations based on those figures. The sensors that have some importance are:

I’m not going to go into a lot of detail here about what each of these sensors does, but I made a link to some info about a few of them. I will limit the info here to the main/important points of some of them.

Mass Air Flow – Measures the air coming into the engine. Basically, a little wire heats up, air passes over the wire and cools the wire in relation to the mass of air that passes over it.

Intake Air temperature (IAT) – Measures the temperature of the air as it enters the engine.

Manifold Temperature – The manifold temperature sensor provides a reading of the heat soak in the intake manifold, because that heat can change the density of the air going into the engine (because this is right before the air enters the cylinder). The idea here is that an added adjustment can be made to compensate for this heat soak.

Coolant Temperature – Precisely what it says.

Throttle Position Sensor (TPS) – The throttle position sensor tells the system not only where your foot is on the pedal, but how fast you are making a change in either direction; faster or slower.

Manifold Absolute Pressure (MAP) – Measures the pressure of the air in the manifold, which can be used to calculate air mass if you have other known figures (like temperature). I imagine at this point you are starting to notice that everything is about the mass of air and the quantity of fuel to add to such mass to make things go.

Crank Position Sensor – Tells the ECU how fast the crank is spinning.

Cam Position Sensor – Monitors where in the stroke cycle #1 piston is located. This way the engine knows which cylinder will have the fuel injected at the correct time.SIDE NOTE: If you are unfamiliar with what a cam is or does, take a look at this animation. A “cam” is a mechanical linkage that makes rotating motion convert into linear motion. If you watch the animation, you notice that while the round portion of the cam is rotating against the lever the valve does not open, but when the oblong portion reaches the lever, the valve opens.

Oxygen Sensors (O2) – Give us a measure of the amount of oxygen that is exiting in the exhaust. If there is excess oxygen in the exhaust, we can assume that more fuel can be burned.

Knock Sensors – Pick up sounds caused by detonation.

Try to think of all these sensors as a loop. They feed information to the ECU (the brain) and as calculations are made the settings change and new information is received. The O2 sensors are in the exhaust, the others are in front of the cylinder. The sensors in front of the cylinder send the information to the ECU, the ECU makes an educated guess as to where things should be, then the O2 sensors read the outcome and determine how well the ECU made it’s guess.

In part III of this tuning series we will take a look at some basics of fuel and ignition systems