MAF FAQ (long)

[Robin-535im]

I'm curious to learn more about DME and MAF's.

Here's my understanding: DME uses O2 and MAF readings to determine a/f ratio and air flow rate, then uses this to look up on the chip timing and fuel tables what the timing advance and fuel duration should be.

Adding a MAF tricks the DME into thinking the air flow rate is different, so it looks at a different place on the chip and chooses a different timing and fuel pulse duration, right?

Then why can't you just reprogram the chip maps to mimic the effect the MAF adjustment has?

Also - won't the O2 sensor see that the ratio is not as expected and continue to correct the mixture? I would think you'd want to tweak the MAF readings and the O2 readings too, so that the DME happily thought it was running a/f 14.0 when it was really 13.5, etc.

Also again, BillR told us once (where is he BTW?) that the reason the car has more power when cold is that the DME is not in closed-loop mode with the O2 sensor, instead it's running open loop and you're not operating at the programmed a/f ratio. Is that the same basic effect you get from a MAF, you can run the car at different a/f ratios and get some of that lovely cold-engine-power back all the time?

- Robin

[632 Regal]

damn...thats deep!

[Unregistered]

damn...thats deep!


post whore

[Martin in Bellevue]

Pull the stock air meter for a look at the cross section available for air flow. The stock air meter is the big restriction between the air filter and the throttle. The stock vane type air meter is a flapper which opens as the intake flows along.

Bruno's MAF kit includes a controller which allows for signal conditioning everywhere along the rpm range. This signal seems relevant, up until a certain rpm at wide open throttle, then a different set of maps are used by the dme, ignoring air meter signals.

[winfred]

ditto, a maf is bigger then the afm and you are not sucking that spring loaded door open, plus it should have a faster reaction time to throttle inputs and gives you the option of fine tuning the mixture


Pull the stock air meter for a look at the cross section available for air flow. The stock air meter is the big restriction between the air filter and the throttle. The stock vane type air meter is a flapper which opens as the intake flows along.

Bruno's MAF kit includes a controller which allows for signal conditioning everywhere along the rpm range. This signal seems relevant, up until a certain rpm at wide open throttle, then a different set of maps are used by the dme, ignoring air meter signals.

[Jeff N.]

Here's my understanding: DME uses O2 and MAF readings to determine a/f ratio and air flow rate, then uses this to look up on the chip timing and fuel tables what the timing advance and fuel duration should be.

Sorta. I thinks it's like the DME specifies an injector pulse duration and ignition advance setting based on engine RPM and a load factor that is basically determined by the AFM voltage signal.

The Lamda signal is used to trim the fuel pulse within a narrow range to minimize emissions via maximizing the effect of the cat converter. My understanding is the converter works best in a very narrow chemical range.


Adding a MAF tricks the DME into thinking the air flow rate is different, so it looks at a different place on the chip and chooses a different timing and fuel pulse duration, right?

Yes. It can do that. The lastest Pro-Flow unit (nicely value added by Bruno at Racing King with a custom harness and intake plumbing) has a black box that allows you to "condition" the input and output voltage of the MAF to spoof the ECU. I think this is best viewed a way to fine tune the map signals vs. gross adjustments. Gross adjustments need to be done via the chip.


Then why can't you just reprogram the chip maps to mimic the effect the MAF adjustment has?

Martin and Winfred discussed the other benefits. :)


Also - won't the O2 sensor see that the ratio is not as expected and continue to correct the mixture? I would think you'd want to tweak the MAF readings and the O2 readings too, so that the DME happily thought it was running a/f 14.0 when it was really 13.5, etc.

Hmmm...the O2 sensor tries to get the a/f mixture in the best position for emissions, not power. Maybe a well setup chip/MAF unit might make the most power in open loop not closed loop? Hmmm...and you plug in the sensor to make emissions. Hmm...now that's an interesting thought, no?


Also again, BillR told us once (where is he BTW?) that the reason the car has more power when cold is that the DME is not in closed-loop mode with the O2 sensor, instead it's running open loop and you're not operating at the programmed a/f ratio. Is that the same basic effect you get from a MAF, you can run the car at different a/f ratios and get some of that lovely cold-engine-power back all the time?

Maybe if you run it open loop so the O2 sensor doens't try to correct the mixture back to stoich.....

Good questions...I'm still tinkering.. :)

Jeff

[Robin-535im]

I think this is best viewed a way to fine tune the map signals vs. gross adjustments. Gross adjustments need to be done via the chip.


Since that's the "Gross" adjustment, I would think you would get the biggest bang by custom chipping, then tweak that with the MAF...

It's not hard to do at all, though the burner ("toaster?") is a capital outlay.

Also - since were're here - they have in circuit emulators that mimic the EEPROM behavior in the DME but are controlled with a PC, not a chip. That means you could reprogram your chip on the fly, to meet the conditions at hand... I bet a good controls engineer could put together a custom O2 sensor, MAF, and a EEPROM emulator to get max power for any given configuration. You could even program a "learning" mode where you drive around for a while and the thing optimizes the setup in real time...

I'll do the engineering if you buy the parts :)

- Robin

[bahnstormer]

from the sounds of this, a EAT chip and maf wouldn't play together too well
that sound right?

[Robin-535im]

from the sounds of this, a EAT chip and maf wouldn't play together too well
that sound right?

Considering how adjustable the MAF is. Just set the MAF to give the exact same readings as the stock, and all you have is the stock setup with better airflow.

Now, it could be said that a stock EAT chip would be outperformed by a custom chip tuned to that particular car, but I think the combo of EAT + MAF is an improvement over either by itself, unless the MAF is poorly tuned - which is certainly possible judging from how sensitive the MAF tuning is.

[Jeff N.]

Yup. No problems of a MAF working with an EAT or any other chip.