The Role of a MAF

[BADfish10]

Hi Guys

I have been thinking and looking around but have been unable to find a good answer to my slightly odd question.

Most modern EFI engines us a MAF of some form to measure airflow the most common type being a hot wire MAF this effectively gets cooled as air is passed over it, the cooling effect changes the wires electrical resistance the ECU monitors this and along with the known area of the MAF tube makes calculation to help with fuelling?

So my question is if an engine is running individual throttle bodies without MAF’s how the is the fuelling effected. I assume as there are a fair number of engines out there running ITB’s and aftermarket management it is not essential to have accurate MAF data to correctly fuel an engine, with this being the case how do they get round not having MAF data is there a reliable way to use just the Lambda data for fuelling ?

Cheers in advance

J

[gazza82]

ECU will probably need to be remapped ...

[biffa]

I think it got more to do with Emmision control...

[Cream]

there are a few different ways an ecu can control engine fueling. road cars use maf sensors becuase they give very good economy over a wide range of conditions and countries, also the emsssions are very important

for high power applications, fuel economy is of very little importance, as are emissions. an ecu can simply measure the throttle valve angle, measure air tempreature and use a map set up on a rolling road to fuel the engine accordingly

you can also use a map sensor on the intake manifold, (mass air pressure) the ecu can take enough data from this to be able to run the engine, if you do a search for aftermarket ecus - emerald etc, they discuss all the options for running engines

also the maf, yes most modern engines run with hot wire types, however the ecu is actually measuring the current flowing into the maf, as air passes through it, the wire or resistor cools, but the the ecu then changes the voltage to keep the current constant, so it actual measures how much current it takes to keep the wire/resitor at the same tempreature for a given airflow

[Cream]

Blog - The Injection System at Work

[BADfish10]

Thank you Cream that is realy helpful i will go and do some reading on MAP vs MAF.

[BADfish10]

Ok so have done a bit more reading on MAP and MAF's and the do pretty much the same thing but in vastly different ways! With my current understanding i am starting to think that you could build a MAP to MAF converter. By using something like an arduino to take the input From a MAP sensor reference a conversion table and give out the expected data from a MAF. I’m going to look a little more deeply into how often the MAF data is used and what the pure data looks like as this will dictate the required speed of processing unit.

Edit:
Update I’m going to order a Arduino and a Map sensor tonight as it is looking fairly do-able in terms of hardware and Code as there should be a strong correlation between data.
I will start a new thread once I make a start in earnest

Thanks for the pointers

J

[Cream]

what are you actually going to do, you can build a converrtor using a pic, i guess thats what a Arduino is ?

but the boash AFM is a very senbsitive instrument, the map sensor is a 20 pence sensor, its not as accurate

also you can just use throttle fap position and caculate the the airflow into the engine - volume of the cylinders * revs and the ecu can supply fuel as neccessary

is this for you gtv ?

[ChrisS]

Simplest form of contol is *****/N as Andy says. Basically, throttle angle and engine revs. to point to a map cell, fuel then comes straight from the map (with tweaks for temp etc). Works pretty well too. Our Westfield uses this to control the Zetec engine. ITBs, throttle postion sensor, a crank postion sensor and a water temp sender - that's it. It can support closed loop using a Lambda, but I never bothered. It starts on the button any temperature with no fuss, drives great, makes good power and is economical.

As already mentioned, it's a lot to do with emissions control, but using a MAP or MAF (or both) can give really fine control and great driveability on light throttle.

MAP with ITB's can be troublesome with lumpy cams but is often done well enough by damping the signal.

Have tried various versions of the above on a couple of Busso engines. used to run a V6 Alfa/N, then a blended Alfa/N MAP setup then finally the same but with it boosted....and to top off, some closed loop adaptive control of mixture using a wideband.

The key to good results with aftermarket ECUs is getting a good map in there to start with. A combination of a good RR operator followed by some road use and fine tuning will get you to a decent result.

Don't forget igniton timing while you are at it.


Enjoy!

(A decent MAP sensor starts at about £70 BTW, avoid the cheap ebay ****e unless you want to drive yourself nuts trying to figure out the transfer characteristics!. I did hear of one supplier selling empty plastic housings - no sensor or electronics in them at all.....)

[ChrisS]

I love the way this site blanks out A L P H A as a swear word...

that was A L P H A /N by the way. Denoting (throttle) angle vs. (engine)speed.

[Cream]

Originally Posted by ChrisS

I love the way this site blanks out A L P H A as a swear word...

that was A L P H A /N by the way. Denoting (throttle) angle vs. (engine)speed.

quality

[BADfish10]

Thanks for the input guys
The arduino is a single-board microcontroller that can be used to read sensor inputs and make output in both digital and analog signals, it is not the most advanced system on the planet but it should be quicker than the ME3.1 data processing and that is all that is needed.

I am getting a few as they make great toys and i had an idea:
If I can generate a signal the same as a ECU would expect from a MAF (0-5v) then it should be possible to run a computation using different inputs “from a MAP sensor for instance” cross reference a MAF/MAP table and output what the ECU is expecting. It would also be possible to upgrade to a bigger MAF and write an equation that would correct the input for the ECU.

With all this now said I have started looking at 3rd party ECU’s to allow for a longer term plans, however I may still have a go with the MAF/MAP as I need a code project to get me going

Thanks