MAP/MAF regulation question

[jamesNewman]

I'm sorting out what's needed during the winter for my Improved Touring build and I've been unable to make heads or tails of a couple parts of the rule book regarding MAF's and MAP's, it seems to be a bit muddled.

D.1.4 states:

All air entering the intake tract shall pass through the carburetor or fuel injection air inlet. All air must also pass through the stock air metering device, eg MAF, or AFM, etc if so equipped. Air intake source shall be within the confines of the engine compartment or stock location.

and D.1.6 states:

The engine management computer may be altered or replaced. A throttle position sensor and its wiring may be added or replaced. A MAP or MAF sensor and its wiring may be added. Other existing sensors, excluding the stock air metering device, may be substituted for equivalent units.

Now, can I have it so that air is passing through an inactive MAF (since it has to be there and D.1.4 states it must pass through it) and a MAP is doing all the air metering for my motor?

I'm not trying to cheat or be a d-bag, it's just all the ignition systems I've worked on and wired use MAP's and my 85 MR2 utilizes a MAF.

[Greg Amy]

...can I have it so that air is passing through an inactive MAF (since it has to be there and D.1.4 states it must pass through it) and a MAP is doing all the air metering for my motor?

Yes.

[seckerich]

To add to what Greg said. Yes, you do not have to use the feedback from the MAF to the computer, but it must be unmodified in any other way. No gutting or other changes to improve airflow.

[JeffYoung]

Keyrect, and that is where the temptation lies. You can't touch that stock flapper!

[Andy Bettencourt]

Keyrect, and that is where the temptation lies. You can't touch that stock flapper!

Typically found in a AFM. MAF's come in many flavors. Plunger types, pass through types, hotwire types, etc. No physical mods, just your ECU doesn't have to 'listen' to what the mecahnics are telling it.

[pfcs]

"Keyrect, and that is where the temptation lies. You can't touch that stock flapper!"

Do the current rules allow changing the resistance of sensors??

[Eagle7]

"Keyrect, and that is where the temptation lies. You can't touch that stock flapper!"

Do the current rules allow changing the resistance of sensors??

Are you talking about electrical resistance (ohms), or mechanical (spring rate)?

[Chip42]

agreed with the others but also remember that the MR2 stock wiring has the fuel pump circuit running through the AFM as a safety(switched)- just keep it in mind while you're wiring it up.

[pfcs]

"Are you talking about electrical resistance, or mechanical (resistance)? "

Resistance is resistance! What does the RULE say?

[Eagle7]

"Are you talking about electrical resistance, or mechanical (resistance)? "

Resistance is resistance! What does the RULE say?

The word "resistance" does not appear in the ITCS. The only allowance I see is

A throttle position sensor and its wiring may be added or replaced. A MAP or MAF sensor and its wiring may be added. Other existing sensors, excluding the stock air metering device, may be substituted for equivalent units.

and then there's

On cars so equipped, the air metering/measuring device (i.e. air flow meter, air mass meter, MAF) must be operational and shall not be modified.

[pfcs]

Thanks for the clarification-then changing the resistance of a L jet AFM isn't allowed. No problem. Just wondered.

Are you sure there's no allowance for altering resistance?

[Eagle7]

Are you sure there's no allowance for altering resistance?

Every time I think I'm sure of something in the GCR somebody like tGA steps in and throws me for a loop. I'm just reading the same book you've got.

[Greg Amy]

There's a thinkin'-man I can ree-specht....

The "resistance thing" for the sensors was there some time ago, but it went out with the open ECU allowance...so you're not crazy...

[GTIspirit]

Thanks for the clarification-then changing the resistance of a L jet AFM isn't allowed. No problem. Just wondered.

Are you sure there's no allowance for altering resistance?

I would argue to the contrary. Under the programmable ECU allowance where does it specify what kind of tuning is allowed? It doesn't specifically state that tuning must be done with ones and zeroes. The old school mechanical fuel injection, such as K-Jet and KE-Jet did in fact use resistances for calibration. The rough fuel quantity adjustment was done with the fuel distributor. The KE-Jet "AFM" position potentiometer helped with the fine tuning. Changing the resistance of this potentiometer would be the same as changing the linearization curve on a modern MAF or MAP sensor, which is clearly allowed under the programmable ECU clause.

BTW, what happens if two rules are clearly in conflict? In this case the programmable ECU rule conflicts with the no modifications to factory MAF/MAP (the intent of the rule was no physical modification to reduce restriction, I doubt the intent was no electrical modification because then unplugging the sensor or changing linearization curves would not be allowed) because the programming is done through different means due to the different sophistication of the ECU's.

[JeffYoung]

Sorry, I don't see a conflict. ECU rule allows you to use whatever tools the ECU gives you to tune it. Tuning external inputs, like those to a mechanical system, is not allowed except for specific sensor allowances. May not be fair, and maybe should be looked at, but it what it is.

Second, the AFM/MAP/MAF rules are finally, in my view, clear. You have to leave the stock device in place, but there is no requirement that you use a signal from it to "run" the ECU. The intent was to allow whatever piggyback air measuring device you needed to get your car to run (MAP, MAF whatever), but you had to leave any "natural" restriction in airflow in the intake tract.

[GTIspirit]

There's more than one way to alter the resistance of the L-Jet airflow sensor, without modifying the sensor itself. There are also resistors inside the ECU that would do the same thing and which are probably the preferred approach, if you can understand this diagram and it is the exact diagram for the aforementioned L-Jet.
http://www.205gti.com/bosch/ljet_drw.pdf

[lateapex911]

There's more than one way to alter the resistance of the L-Jet airflow sensor, without modifying the sensor itself. There are also resistors inside the ECU that would do the same thing and which are probably the preferred approach, if you can understand this diagram and it is the exact diagram for the aforementioned L-Jet.
http://www.205gti.com/bosch/ljet_drw.pdf

The crux ...

[pfcs]

"There's a thinkin'-man I can ree-specht....

The "resistance thing" for the sensors was there some time ago, but it went out with the open ECU allowance...so you're not crazy..."

So many minds/so little time
Only Greg seems to pay attention.

I'm a shameless liberal but I believe the rulebook should be taken quite literally. If it doesn't say you can, I won't do it (change the resistance of the airflow meter/sensor, or whatever)
Rules are not ment for breaking.

[JoshS]

The "resistance thing" for the sensors was there some time ago, but it went out with the open ECU allowance...so you're not crazy..."

The open ECU allowance didn't change anything about sensor resistance. I just went through the '05 GCR (the earliest I have handy) and didn't see that allowance anywhere. Maybe it went out with the "in the box" rule and not the "open ECU" rule?

[Greg Amy]

To the original poster: "Yes."

Maybe it went out with the "in the box" rule and not the "open ECU" rule?

Very likely. It was an allowance to "trick" the ECU to behave differently (e.g., not go into limp mode when coolant temp got above "normal"). Seems reasonable that once we allowed alternate ECU programming with soldered chips and daughterboards that it was no longer needed...

To really mess with one's brain, note that engine compartment wiring is free...and resistors are wires, as are several other types of conductive materials...let the brain run free...hey, just sayin'...