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MAF Tuning – When Not To Do It

3 min read
MAF curve

MAF Tuning & Scaling

Here are some things to consider before you start MAF tuning/scaling your MAF signal.

How MOTEC use closed loop lambda control

Type of Lambda Sensor on Engine

Regardless of the type of lambda sensor, narrowband or wideband, adjusting fuelling at idle is probably going to be pointless.

The engine ECU is going to attempt to meet it’s target AFR regardless of the MAF tuning you do. And if the ECU is trying to do what it thinks is too much to achieve it’s target, it could throw a CEL.

Wideband Lambda

If your engine is using a wideband lambda sensor, it is going to be looking at that sensor signal all of the time. Any changes you make that conflict with it’s AFR target are going to be undone.

Narrowband Lambda Sensors

Narrowband sensors are used (closed loop) by the engine ECU at idle and at light load conditions. Outside of this there is a fixed map and this is where we can alter fuelling by altering the MAF sensor signal (because the ECU does not know the AFR of the engine).

When Is Engine In Closed/Open Loop Mode?

Most OBD2 scanners will be able to show live data from the ECU which will display when the ECU is in closed loop and open loop fuel control.

ECU Undoing Changes

In short, the signal coming from the lambda sensor is usually king for engine’s ECU when it comes to fuel tuning. In conditions where the engine ECU is using the lambda sensor, the lambda sensor will dictate fuelling, not the MAF sensor signal.

How to overcome the engine ECU’s reliance on the lambda sensor

Disconnection

On some vehicles simply disconnecting the lambda sensor will make the ECU run in a known safe map (and give a check engine light, possibly). This gives a stable base on which to adjust the MAF signal. On some vehicles this will work but on some vehicles this will not work.

Narrow Band/Wideband Lambda Simulation

If you want to alter fuelling when the engine ECU is in closed loop lambda control, you may have joy using a device that simulates a lambda signal. But in these circumstance we will not be tuning the MAF signal so outside the bounds of this article.

Is MAF Tuning Correct For Your Situation?

You need to know 3 key things to asses whether MAF tuning is correct for a specific engine.

What type of oxygen sensor is being used

Under what conditions do you need to adjust the fuelling.

To adjust fuelling on an engine ECU which is constantly in closed loop mode (wideband sensor), MAF tuning and sensor manipulation in general, is probably not the correct route.

When an engine uses a narrow band sensor and you only need to adjust fuelling in open loop conditions, MAF tuning may well work.

Please note, all information in this article is targeted at vehicles used in motorsport and/or off road use only.


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