https://www.landyzone.co.uk/land-rover/td4-basics-for-newbies-or-the-confused.297916/


Watch the video, at around 3 minutes in he messes with the air filter, you can see the MAF on the left next to the filter with the connector sticking up.
Mike

I am talking about the MAP sensor, not the MAF. Just been and taken a couple of pics. Its on the inlet manifold to the left of the Air temp sensor. I will upload the pics from my phone.

Pictures of the MAP. It's down there

Ta

Oh gawd, I'm confused.

Can somebody explain what the MAP and MAF both do, their functions and how they effect engine function when FUBAR'd please?

not my words, taken fromt net
The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an internal combustion engine's electronic control system.

Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion (see stoichiometry) and influence the advance or retard of ignition timing. A fuel-injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow. A typical naturally aspirated engine configuration employs one or the other, whereas forced induction engines typically use both; a MAF sensor on the intake tract pre-turbo and a MAP sensor on the charge pipe leading to the throttle body.

Dartmoor Navigator said:

Oh gawd, I'm confused.

Can somebody explain what the MAP and MAF both do, their functions and how they effect engine function when FUBAR'd please?

Click to expand...

Quite simply - a MAP is a 'Manifold Absolute Pressure' sensor -
Wiki is good here
The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion
It is easy to see that if you know the temperature of the air and also the absolute pressure, then one can determine the MASS flow rate. The oxygen content of air is stable (within reason) hence increasing pressure and temp readings will allow the ecu to calculate the the desired fuel quantity to be injected.

The MAF is a secondary device - (on a Diesel -)
A fuel-injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow. A typical naturally aspirated engine configuration employs one or the other, whereas forced induction engines typically use both; a MAF sensor on the intake tract pre-turbo and a MAP sensor on the charge pipe leading to the throttle body.
There are instances where the MAP cannot accurately control fuel mix depending on ECU config - often with EGR and other emission controls. The MAF tends to use a hot wire arrangement where a preset heating is applied to a wire grid - more airflow - a greater cooling effect hence a measurement of mass (based also on air temp)
The key is the air / fuel ratio is determined by the MASS of air entering the engine - the oxygen content will vary with temperature according to Boyles law.
One needs (or - the ECU - needs) to know both the MASS and the temperature - which is also proportional to the air temperature..
Stoichiometry is simply the relationship of a given mass of air to a given mass of fuel for ideal combustion in the given circumstances.

All good fun

Basically and I am no expert in this.
The sensor sends a reading to the ECU which in turn uses it to optimise the running of the engine.
The ECU has defaults for some sensors if they stop sending readings so it will run but not as well. Thats why people are told to unplug sensors like the MAF as that has a default in the ECU. If it runs better or the same when unplugged its like the MAF is not working correctly.
For sensors that the ECU does not have default it either runs like pig, goes into a safe mode or does not run at all. All depends on the complexity of the ECU and whats not working correctly.
Someone will be able to explain in more detail and more complexity but I think thaats basically it.

Joe_H said:

whereas forced induction engines typically use both; a MAF sensor on the intake tract pre-turbo and a MAP sensor on the charge pipe leading to the throttle body.

Click to expand...

Just to correct the above - forced induction on a DIESEL does not REQUIRE a MAF sensor but is useful - on a forced induction Gas engine - the Map can go negative value hence more reliance on MAF...
AN interesting balance that can be sorted out by more complex ecu units