EJ MAF sensor quick question.

SuBaRiNo · Post by **SuBaRiNo** » Mon Dec 17, 2007 9:43 pm

Do these measure air temperature as well as obviously the amount of air the motor is swollowing??

Dave

Gannon · Post by **Gannon** » Mon Dec 17, 2007 10:07 pm

I dont think so.

I know with the l series...

Flapper mafs had a temp sensor because the flap measured air flow and it needed air temp to calculate actual air mass.

Hotwire mafs measure air mass directly by measuring the air's ability to cool a piece of wire. The denser the air, the more it cools.

SuBaRiNo · Post by **SuBaRiNo** » Mon Dec 17, 2007 10:40 pm

Hmmm ok.. i will explain my trian of thought here.... if one was to put a Supercharger on an Ej22 after the MAF sensor it would read incorrectly due to the air being heated by the SC. Which would change the density of the air. This sound right at all.

Dave

Matatak · Post by **Matatak** » Mon Dec 17, 2007 11:14 pm

i was surprised when i didnt find a MAF sensor on Subafurys car once. i think it had a air temp sensor after the intercooler tho.

AndrewT · Post by **AndrewT** » Tue Dec 18, 2007 12:49 am

Matt's car doesn't need one due to the aftermarket Microtech ECU. It's a map based ECU, it tells the engine what to do according to it's pre-set map and doesn't care about silly things like air flow

**sorry to hijack dave!

Suby Wan Kenobi · Post by **Suby Wan Kenobi** » Tue Dec 18, 2007 3:24 am

SuBaRiNo wrote:Hmmm ok.. i will explain my trian of thought here.... if one was to put a Supercharger on an Ej22 after the MAF sensor it would read incorrectly due to the air being heated by the SC. Which would change the density of the air. This sound right at all.

Dave

Yes it would try to compensate for the extra volume of air being drawn in over the NA it would read it as a cooler charge

SuBaRiNo · Post by **SuBaRiNo** » Tue Dec 18, 2007 8:01 am

Thanks that clears that up.

AndrewT wrote:Matt's car doesn't need one due to the aftermarket Microtech ECU. It's a map based ECU, it tells the engine what to do according to it's pre-set map and doesn't care about silly things like air flow
**sorry to hijack dave!

Don't worry Andrew, Matatak almost makes a hijack post in every thread.

Dave

discopotato03 · Post by **discopotato03** » Tue Dec 18, 2007 9:20 am

In a nutshell yes , MAF sensors DO measure air temperature .
A compressible gasses density is dependant on its temperature - and density is directly related to mass or weight .
A hotwire sensor is called a "Mass Air Sensor" or "Mass Air Flow (MAF) because its measuring the amount of air passed by mass . Air/fuel ratio is a ratio of air mass to fuel mass so if you look at the theoretical 14.7:1 ratio its 14.7 units of air by mass to 1 unit of fuel by mass .

In OEM apps MAF sensors are placed between the air filter and the throttle body and upstream of any turbocharger or supercharger . Its done like this because they want to measure ambient conditions existing at the time .
Its a very effective/fast/accurate way of telling the computer how much air's inbound to it can inject the appropriate amount of fuel to achieve the desired air/fuel ratio . Most late systems do ignition timing control as well so between the MAF/TPS/coolant and knock sensors its fairly easy to control whats going on in the combustion chambers .

I get the feeling you are asking this because you'd like to know if it can work with a supercharger on an otherwise std engine/ECU system . The answer is highly likely to be no , not properly because the ECU's mapping is to suit an NA engine and the volumetric efficiencies an NA engine normally has . If you could alter the ECU's mapping and possibly the MAF sensors flow range then yes it can be made to work . A nasty little part of late engine management is that it knows to look for things like MAF's running higher airflow rates that it should in the NA application , it thinks the sensor is giving the wrong signals and generally goes into damage control mode ie rich and retard or some kind of limp home mode .

To do what you want really requires some kind of plug in programmable ECU that uses all your current engines sensors inc MAF . That way a tuner can set the air/fuel ratios and ignition timing to suit the unique engines requirements right across the whole engine speed and load range .
I think you may find that had Subaru supercharged that engine it would have had a lower compression ratio as part of their detonation suppression strategy . Normally the main differences between NA and forced induced engines are the pistons and camshafts , good ones also use piston oil squirters to cool pistons that live in a higher temperature/pressure state when the engines running on boost - generally means a higher volume oil pump too . Also beefier connecting rods are often used to withstand the higher power loads created by higher cylinder pressures .

Cheers A .

Matatak · Post by **Matatak** » Tue Dec 18, 2007 6:46 pm

that was in no way a hijack post..i was implying u shuld find an aftermarket ECU which doestn need one...liek Subafurys.

PeeJay · Post by **PeeJay** » Tue Dec 18, 2007 6:51 pm

Don't EJ Turbos have the MAF before the turbo? Or is that something different?

Post by **Alex** » Tue Dec 18, 2007 7:32 pm

seeing as though the question has been answered, id like to add my liberty doesnt seem to have one either....(not that i can see anyway)

alex

Gannon · Post by **Gannon** » Tue Dec 18, 2007 9:51 pm

It wont matter where you place the MAF.

It measures air mass.

If you mount it before the supercharger, it will read a certain amount of cold dense air
If you mount it after the supercharger, it will read a higher volume, but a lower density and the overall mass read by the MAF will be the same