86 951 Driver

I just found this website and am starting to look more into this.
http://www.carlton24v.co.uk/afmmaf.htm
It has the conversion concerning another car with the BOSCH Motronic system. If one of you very knowledge car people could look at this maybe we could all benefit and make our own MAF kits at our houses.

theedge

Now that looks like a good find, except that hes keeping the code for the microcontroller under his hat for now as he puts it... Then he mentiones kits for sale...

86 951 Driver

I figured that with this info though someone here could help to make the code. I can't do that because I don't do programming at all. I can do html but that is it. I know what it takes to make a car fast but I don't have the knowledge of computer programming to program my own chips that and I don't have chip burner. I just am looking for a way to get a MAF on my 924S to help with performance.

MM951

Can 951s use a GM MAF setup? The MAFs are like 50$ (You need a LT1/LS1 one) and the translator is only like $100....

awilson40

I thought the Lindsey MAF was already calibrated to match the stock AFM flow???

DDP

The old SFR MAF for the Turbos are Ford thunderbird sensors. Just go to the junk yard, find yourself one, and build it. You just need a higher voltage power source and the chip to run it. The stock power source is 5v and you will need 12v for the hot wire sensor. Good luck.

nine-44

If I'm not mistaken, the GM sensors use a frequency signal, not a voltage signal that the motronic will read. I'm pretty sure that the Ford EEC IV engine management systems that use the hotwire are all a 5V signal. I did a bunch of homework on it, but have no way to read, breakdown or write the code for the chips that would translate the signal accurately. In therory you could just plug a hotwire MAF in, run 12V to it and the signal out would be kinda close, but not enough that a signal controller would be able to tune out and correct. the CFM vs voltage in a MAF climbs in a straight line, the barndoor in the AFM swings in an arc, the further it opens the more the voltage reading curves. The computer would read it as a completely different ammount of air comming in. Back to the drawing boards, lol.

Danno

Problem too is the max-flow rates at 5v max-voltage output. If you've got a MAF that's calibrated exactly like the AFM, you can't measure more air than stock. At 250rwhp when the AFM maxes out, the MAF will be maxed out and give you a flat-lined 5v output. If you hit this flow-level at say... 4500rpm, the computer won't be able to tell that air-flow is increasing as RPMs increase and you'll get a leaner and leaner air-fuel ratio as RPMs increase..

awilson40

So what do you do to correct that problem??
Is that the main purpose of a piggy back controller...to skew the MAF signal
down so it doesnt max out to early??

Danno

Can't do that either because you still get a flat-line signal, just lower. Once the sensor is maxed out at 5v and flat-lines, massaging it will give you a flat-lined lower or higher-voltage, but it cannot convert a flat fixed-voltage signal into a rising one to match air-flow. For example:

RPM VOLTS
----------------
2000 2.5v
3000 3.5v
4000 4.5
5000 5.0
6000 5.0
7000 5.0

You can tweak the signal all you want, but there's no way you can make those last three rows anything but flat.

What you're talking about is developing your own MAF kit. You'll need the following:

- MAF sensor with appropriate CFM flow-rate for intended usage
- flowbench
- datalogger and/or 'scope
- custom chip-mapping software
- customized chips appropriately mapped for that particular MAF sensor

This is the sensor itself, you'll need to fab up pipes and stuff to make it fit. Then you'll also need wiring connectors to connect it to the stock harness. All of this is a lot of work, will take you about 50-100 hours. What kind of wages can you earn in that time? Why not just buy one of Vitesse's or Lindsey's MAF kits with the money that you can make in that time?

BTW- that original link above was for converting NA AFM to MAF sensors. Not that it would make much of a difference, perhaps 5hp max. It can be done in that case with NAs because their max-flow rates won't change much, so a MAF can be calibrated to match the AFM and it will work. But on a Turbo, you want to be able to increase the boost and have it accurately measured. Which means a MAF that can measure 50-100% more air than the stock AFM.

awilson40

Way over my head
But it is interesting.

Zero10

A situation like this should only arise when the MAF used is too small for the application.
Remember, if there was no difference in signal reported between the airflow at 5000rpm vs the airflow at 7000rpm, it wouldn't have worked very well on the car it came from.

I wonder, if somebody like FRWilk might be able to help out in the development of a cheap(er) MAF kit. He seems very knowledgeable with the Bosh Motronic system, and very able to burn chips. Then again, the chips might be just as expensive as his power prom's.

A friend of mine has an EEPROM burner, I'll give him a shout, perhaps he might be able to help in the chips department.

If somebody was able to read/write the chips, and knew at least a little about the functionality of everything inside the DME, there is a good chance I could lend a hand on the computer side of things. I'm in the midst of several low-level programming and I/O courses right now.

Zero10

Hmmm, I just did some reading on what this guy used, and all of the company web sites involved. I know what I'm asking for for christmas. I'm gonna get one of the PIC programmers, compiler, chip, etc from the microchip web site.

I like to think I'm well versed in low-level programming on miscellaneous devices, let's see how good at it I am.
My biggest worry, is that the chip he used barely has enough memory for the maps. If he wanted to use a 12 bit or 16 bit DAC, he would be up the creek. Also, the ADC onboard is only 10 bit, so it would require an external ADC to gain higher resolution.
I think I'll order it with one of the fancier chips, lol.

nine-44

You can however, oversize the AFM or MAF and proportionally oversize the injectors to match. The MKIII Supra guys do the Lexus MAF upgrade with the 440cc injectors all the time successfully. I don't know of the airflow vs cc flow and how they would proportionally rize, but with a little research, I'm sure you could do it on a 944, NA or turbo.

89magic98

I thought our DME's had some Intel 8051 variant in there.

Zero10 - maybe you should look in the back of Popular Electronics magazine (I think it's called Poptronics now), they sell lots of 8051 evaluation boards in there. You probably want one with an A/D converter in there so you can measure voltages like you would need to do in this application.