MAF frequency

[paulg23]

Hi - I am lead to believe that the airflow signal from the MAF to the ECU is a signal that changes frequency proportional to mass air flow. Anyone have an idea what the minimum and maximum frequencies are?

Thanks in anticipation.

[Nutter_John]

Hi - I am lead to believe that the airflow signal from the MAF to the ECU is a signal that changes frequency proportional to mass air flow. Anyone have an idea what the minimum and maximum frequencies are?

Thanks in anticipation.

From around 10hz to 1700hz but the maf will do up to 3400hz

[paulg23]

Thanks for that John. Once I get my gearbox back in Im going to fit a MAP/Temp sensor and log MAF frequency against pressure, temp and RPM with a view to making a MAP to MAF converter so I can get rid of the MAF and still keep the standard ECU. Anything else I should be logging?

[Nutter_John]

just buy a map2 as it does everything your looking for and needs zero dev time

[Kenneth]

Or give that money to me and ill get my backside into gear implementing speed density into the standard ECU

[paulg23]

map2 = US$400+. Too much as I only want the MAP - MAF function.

[Nick Mann Services]

There is a MAP ECU 1 with less functonality. I guess that would be cheaper...

[Kenneth]

I made one a year or so back. In the end, it wasn't that cost effective.

It might cost $50 for the base electronic components (assuming you have the programmer or it is easily programmed via boot loader) then you need a decent MAP sensor, IAT and baro sensor. You can keep the standard MAF half plugged in and that will save you doing the Barometric signal.

You then have to code a fairly robust signal generator. A in-built timer won't be sufficient unless the micro is very fast. I couldn't get a good linear response above say 1000Hz with a 16Mhz micro using the 16bit timer.
I got around that by implementing a DDS style system using a 32bit accumulator which gave pretty good resolution.

Then you need the mapping. You need to build a 3d map with scalings. You could do them pretty basically, I used configurable scaling and stored the scales and 3d map in EEPROM and loaded into memory for use.

You also need to communicate with it and be able to log it alongside your MAF and IAT signals. I would also use a scope to check for signal irregularity. If the standard ECU uses a compare timer and calculates frequency based on the time for half or full wave signal, then irregularity could cause some odd issues.

Of course you could be very experienced with this sort of thing, in which case it should be easy!
Good luck.

[Mark 4]

Luv ya Ken, but WHAT ?

[Kenneth]

Haha, I probably would have thought the same thing 2 years ago!

Luv ya Ken, but WHAT ?

[paulg23]

The plan was to use a 64MHz micro. Measure the MAF frequency and RPM using the capture/compare module and the MAP and temperature using 10 bit ADCs. Log all of these to build up a MAF-MAP conversion table. Once logged I'll then use the micros PWM to generate the MAF type signals the ECU needs. A 64MHz micro is only £3 these days and I have a C compiler and debugger/programmer.

[Gly]

ken how much to implement speed density? on the stock 7202 ecu

[Kenneth]

Micros are pretty cheap these days, and fast. What micro is it?

Have you looked at using a hot wire style MAF in the charge piping? That was (and still may be) the way I was headed as I like the way the MAF doesn't require re-tuning when there is any change in volumetric efficiency.

[paulg23]

PIC18F25K20. Debugger/programmer is £30 and a student version of the C compiler is available as a free download. I use them at work (amongst others) so already have acccess to all the tools. I wanted to use a MAP sensor so I could get rid of some of the pipework in the engine bay! Fitting a wideband so will be able to monitor the AFRs.

[Kenneth]

Hmm, do PICs still use 4 cycles per instruction? Does that affect the timers and how fast you can toggle a pin via timer overflow etc?

You should be logging from the ECU too as that will tell you what the ECU is trying to do. AFR by itself isn't enough to tell you if you are running into problems. For example, you can't tell if your AFR is changing due to calculated Load or whether it is getting knock and AFR is dropping due to interpolation with the low octane fuel map.

[paulg23]

PICs still divide the clock by 4. I will use the in built PWM to generate the simulated MAF signal.