[jpnovak]

Engine Sensors

I am not going into detail about individual sensors. Each ECU has recommended sensors This topic heading is less about actually collecting data and more about what sensors can do for you including Protection algorithms.

AFR: The wide-band oxygen sensor (WBO2) gives you feedback on air fuel ratios. Can’t have too much or too little fuel. Most ECUs can set up limits to shut down an engine if the AFR goes haywire. These ECUs also have closed-loop auto-correction that can monitor and adjust on the fly while in operation. I think that if you tune an engine well then you can run in an open-loop mode. (closed loop the info is returned to the ecu and readjusts… In open loop the loop is broken or disconnected so no info readjustments)

Temperature sensors: The coolant sensor in an air cooled engine could be cylinder head, oil temp, case temp or several other temperature readings. This is used as part of a warm-up process to add fuel when the engine is cold. This can also be used to enrich or change timing if the engine gets too hot.

The air temperature sensor (commonly called IAT (Intake Air Temperature)) is used to make air density corrections. There are different ways to mount the IAT. This is important. I am a fan of mounting the IAT in the intake stream. This means inside the plenum or airbox so that you can measure actual air temp going into the engine. Yes, air heats as it goes into the engine. And yes, it really heats if you are running a turbo under boost. Yes, you have to compensate. So, Why am I explaining this? All ECUs have an air temperature correction curve. This is to add fuel on cold days and take away fuel on hot days. You can also change timing curves when the engine gets hot. If you are running a hotrod engine you will need to pull timing if IATs get too high. This is one protection to help avoid detonation. Your tuner will help with this setting or your ring lands will suffer greatly. Note, default curves in most software base files are not correct for an aircooled engine. (excellent )

Knock sensors are another way to push performance with protection. They can be used during tuning to setup ideal timing curves and can be used to reduce timing if knock is detected. All it takes is one bad tank of gas. Now, available ECUs can use either an external knock sensor amplifier or an internal amplifier. This takes the small voltage from a piezo electric knock module and scales it into a range the ECU can detect. Our cars can have a relatively high valve train noise that can trigger false knock signals. The knock sensor frequency is based on cylinder diameter and the filters must be setup correctly. Read manuals and act accordingly for your system. . ( consult an expert!!!!!)

Knock Sensors: Knock sensors can be installed in an air cooled motor. These can utilized the mounting stud by Cylinder 3 for a throttle plate, the MFI pump boss, or a 964/993 style cylinder head bridge. The important thing to remember is that you set the frequency of detection to match your engine build. The frequency is related to the cylinder diameter. The typical formula is:

Knock frequency (kHz) = 1800 / (3.14 x Piston Dia (mm))

Make sure when setting up the ECU you get the sensor parameters correct. Knock sensor protection will usually retard timing when detected. Knock sensors can be useful when adjusting the ignition map.

Knock sensors can be electronic or analog. The electronic sensors use a piezo electric detector and must be run through an amplifier. Some ECUs have the amplifier built in but many do not. You can also use a microphone or even a “det can”. All can work well and vary in cost and complexity to install.


The summary here is to make sure that sensor correction curves work for you. Not against you.