What exactly does calibrated for 24# mean?

[DoctorB712]

I have a question, what does that mean when the MAF sensor says CALIBRATED for 24# injectors? So the car has 24# injectors... the cpu thinks 19#, then you put in this magic MAF that fixes things? What exactly does it TELL the CPU? What are the normal MAF voltages and what changes when you change your MAF? Details would be good.

I'm trying to understang our CPU because I think it sucks... that is just my opinion!

Matt

 

[final5-0]

See if this helps shed some light on the subject

Grady

Basic Maf Theory & ProM's "Cheat" Method Explained


Assumptions for this document are that you own a TwEECer or EEC-TUNER
and that you are running larger than stock injectors and/or Mass Air Flow
meter (MAF).

First lets start with a little theory. The way the ford EEC series
processors determine the amount of fuel and calculate load values is by
measuring the amount of air that is flowing into the engine via the Mass
Air Flow (MAF) sensor. The MAF sensor works by heating a wire inside the
sensor. As air flows past the wire it cools the wire. Depending on how
much the wire cools and the radius of the MAF sensor you can calculate the
physical volume of air flowing through the sensor. This measurement is
sent to the EEC processor as a voltage reading between 0 and 5 volts.

The EEC has a 30 point table pre-programmed into it that references a
voltage reading to an amount of air in kilograms per hour (KG/HR). For
simplicity lets pretend it is only a 5 point table and use simple round
numbers to make calculations easier. For example:

5 volts = 1000kg/hr
4 volts = 700kg/hr
3 volts = 500kg/hr
2 volts = 350kg/hr
1 volts = 250kg/hr

The way the EEC works is to reference the voltage signal to a row in the
table. If the voltage falls between two readings it calculates a value
using the surrounding numbers. So if the MAF was sending a signal of 3
volts you would have 500 kg/hr of air flowing into the engine. If the MAF
was sending a signal of 2.5 volts you may expect 440 kg/hr (the scale is
weighted with larger increments in the higher voltage range).

The EEC then uses this table to calculate the pulse width for each
injector to supply the proper amount of fuel to feed the measured air.
This calculation is based on the values in LOW_INJECTOR_SLOPE and
HIGH_INJECTOR_SLOPE (more on these settings later). For now assume that
both are set to 20 to represent a 20lb injector.

Now lets assume you ordered a new MAF meter from Pro-M and had it
calibrated for 40lb injectors (remember, these are all made up numbers).
You installed a fresh set of 40lb injectors and bolt on the meter. How
does the meter make the 40# injectors work with the stock programming? It
does this by reducing the voltage from the MAF meter to represent a
physical volume of air equal to the factory injector size divided by the
new injector size (in this example 20/40 or ½). NOTE: It is NOT reducing
the voltage by this percentage, this is very important to understand. The
reduction in voltage is precisely engineered to make the EEC believe it is
receiving intake air - reduced by this percentage. This means that if
1000 kg/hr of air is actually flowing through the meter it will signal the
EEC with 3 volts (from our table above). This tells the EEC that 500 kg/hr
of air is flowing into the engine and the EEC opens the injectors (that it
still thinks are 20# injectors) for long enough to feed 500 kg/hr of air.
Since the injectors are actually bigger (twice in this case) the amount of
fuel injected is actually proper for the 1000 kg/hr that is flowing
through the meter.

You can also do the math in reverse. At the same voltage reading from the
stock MAF and the new MAF your actual airflow will be new injectors
size/old injector size (in our example 40/20 or 2). So, if the voltage is
3 volts from the new MAF which corresponds to 500 kg/hr of airflow when
you look at the stock transfer table at 3 volts you would see 250 kg/hr of
airflow.

This works fine for most tuning needs but does mess with other
calculations in the EEC like load values. You also don’t have the ability
to accurately scale fuel unless your MAF table accurately represents the
meter and if you plan on data logging it is nice to have the log show you
actual airflow.

For all these reasons and more it is recommended you tell
your EEC what is actually going on by entering actual flow numbers and
actual injector sizes using the TwEECer or EEC-Tuner.

 

[Monsterbishi]

I have a question, what does that mean when the MAF sensor says CALIBRATED for 24# injectors? So the car has 24# injectors... the cpu thinks 19#, then you put in this magic MAF that fixes things? What exactly does it TELL the CPU? What are the normal MAF voltages and what changes when you change your MAF? Details would be good.

I'm trying to understang our CPU because I think it sucks... that is just my opinion!

Matt

When you have a Factory MAF, when the ecu receives the signal it's airflow is based on the assumption that there is a set volume that can flow through it, a MAF that has been 'calibrated' for bigger injectors is just the same sensor, but with a proportionally greater volume, so in the case of a MAF that is calibrated for 24# injectors, the area that air flows through is 26.3% larger than a conventional 19# MAF.

So that means the ecu is then unaware of the extra air entering the engine, which balances out the extra fuel provided by bigger injectors.

This is a bandaid solution though, and only practical for small size changes, since it doesn't allow for injector deadtime compensation, so will lead to low throttle fuelling issues on bigger injectors.

Our ECU's are good pieces of kit, it's the way that people modify things that causes issues.

 

[DoctorB712]

Thanks, thats the type of answer I was looking for from stangnet!!!!

Lets keep on learning about theses cars we have

 

[Pokageek]

Word of caution. I bought 2 MAF's, one was Granatelli, one was Summit. BOTH said they were "cal'd for the 24# injectors" that I have. I put them on and NEITHER ran the car correctly. I thought I had major problems with the car considering the possibilities that 2 MAF couldn't be bad. Alot of $$ later, I had to have the shop custom tune my stock MAF and the car runs again. Just remember, you can't just slap these pieces on unlike what I have heard on the net in general. It just doesn't work that way.

 

[Yobi1Kanobi]

custom tunes with after market mafs is the way to go... you get the maf that is calibrated to your set up and fine tune from there some run fat some run lean.

 

[Pokageek]

custom tunes with after market mafs is the way to go... you get the maf that is calibrated to your set up and fine tune from there some run fat some run lean.

Yes, exactly. For me it wasn't an option without the tune. I wish the place I towed it to could have programmed my summit meter but they couldn't..so I had to put the stocker back on..