MAF Tuning – When Not To Do It
4 min read
One big reason why MAF tuning may not be the correct solution to altering engine fueling is if your engine’s ECU uses a lambda sensor. Here are some things to consider before you decide if MAF tuning or MAF scaling is suitable.
ECU Undoing Changes
If the engine ECU is running in “closed loop” but you want to change the AFR from 12.0 to 13.5 the ECU is going to undo any adjustments you make.
In short, the signal coming from the lambda sensor is usually king for engine’s ECU when it comes to fuel tuning.
The lambda sensor signal, with regards to fuelling, usually takes priority over everything else. If the lambda sensor signal is showing a different AFR to the ECU’s target, the ECU will adjust/readjust fuelling to achieve it’s AFR target.
Increasing the MAF sensor signal may work in the short term but in the long term the ECU is going to start reducing injector duty cycle to get the AFRs it wants.
How to overcome the engine ECU’s reliance on the lambda sensor
Open Loop
If you only want to adjust the engine fuelling when the ECU is in open loop, tuning the MAF sensor signal will adjust the fueling in the short and long term. In short, you probably don’t need to worry about the lambda sensor.
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.
Disconnection
On some vehicles simply disconnecting the lambda sensor will make the ECU run in a known safe map. 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. One way to test if this will work with a specific ECU is to unplug the lambda sensor and see how the ECU responds.
Narrow Band Simulation
Simulating a narrowband lambda signal is also an option. There are many so called “simulators” on the market but the only way we see simulation being done reliably is by using an Innovate Motorsports product which allows you to send a 14.7AFR signal to the ECU at an AFR of your choosing.
For example you may want an actual 15.5 AFR when the engine ECU is in closed loop, in this case we can program with “narrowband output” on the Innovate gauge to send a 14.7 AFR signal to the engine ECU, even though the AFR is actually 15.5.
Innovate Motorsports are the only company we are aware of whose wideband lambda product allows you to program the narrow band signal output.
If your car uses a 0-1 volt narrow band oxygen sensor and you only want to adjust fueling in closed loop conditions, an Innovate wideband lambda sensor is probably the only thing you need.
Wideband Simulation
We know of no product that can reliably simulate a wideband sensor signal. If your ECU uses a wideband lambda sensor signal for the entire time your engine is running, signal manipulation is probably not the way to go. Actually entering the AFR target map inside the ECU and setting the targets directly will probably be the most reliable method.
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 is the engine ECU in closed loop and open loop fuel control
–Under what conditions do you need to adjust the fuelling.
To adjust fuelling on an engine ECU which is constantly in closed loop mode, 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.
If you want to adjust fuelling in closed loop fuel control on a narrow band sensor equipped vehicle, an Innovate wideband lambda sensor with programmable narrowband lambda output is probably the way forward.
And if you want to adjust closed loop and open loop fuelling on a narrowband equipped engine, a combination of an Innovate wideband lambda sensor and a MoviChip MAF Manager will probably be the ideal solution.
Please note, all information in this article is targeted at vehicles used in motorsport and/or off road use only.
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