vaf question

[Chobobulous]

IIRC, the VAF is more load dependent than it is on engine speed. Unloaded tests might not give you the results you're looking for

At the moment i am just getting base values. Tomorrow i plan to wire something up to where i can measure the voltage while driving at different speeds and at different RPMs. I will also use my unmolested VAF so that i get a little more accurate numbers. the brushes on the one i was using to test was a little messed up. I think this, along with potentiometer wear and slight misplacement during reinstalation is what is causing me not to get to the full 4.75 volts.

[sketchman]

So it does in fact work in reverse to what the FSM says from what I'm seeing. Well that's still easy enough to do with the Arduino and nothing else.

Did you happen to check the current draw on the fuel pump switch when closed circuit? I understand in the VAF it's a mechanical switch, but for the Arduino to control it it would have to be able to handle as much current as it is drawing. I think max out on the Arduino is 30mA total.

Nice work, BTW. In theory the Arduino could also make use of the IAT and adjust the VAF sig voltage accordingly if so desired, and it might need to do that to work well enough, but I would hope not.

EDIT: Because this may be the only opportunity to ever say "Thank your girlfriend for me." safely, so I had to.

[Chobobulous]

Unless we are measuring the wrong pins then yes it looks to be opposite. I did not check the current draw, i just assumed it would be 12v straight through. Easy enough to fix though, wire up a kill switch in the car, done. That or hook it to the ignition somehow so that so long that the car was in the on position it would be closed.

Are you planning to use Arduino to make the calculations off the current RPMs?

[sketchman]

It shouldn't need to worry about RPMs if I'm thinking about it correctly. Airflow should be airflow regardless of RPM. If the VAF would normally see a given amount of airflow at a given RPM and throttle position and load and etc., the MAF should see the same amount. The trick will be translating the curve "shape" between the 2. I'm pretty sure the MAF output is fairly linear, and the VAF is obviously not at all but rather starts steep and levels out a bit toward the end.

[Chobobulous]

Ok so you are going to go maf too. What car has about a3 in intake? I was going to go wander around the JY tomorrow toll i found one but if you can help me out that would be awesome.

[Rocketman]

The pump switch fires a relay, the pump does not draw power through the VAF. Write a line in your code that as long as the measured signal is greater than the equivalent for zero airflow, it activates one of the output pins. Use that with a transistor to fire the relay

[sketchman]

^I do understand that the fuel pump isn't drawing power through the VAF. But to close a circuit it does have to draw some power, yes? IF it's a tiny enough draw, then the Arduino can handle it without extra components such as a transistor, because it has plenty of input and output pins. I'll get a reading on it when I can. I'm probably overthinking it. I tend to do that.

Ok so you are going to go maf too. What car has about a3 in intake? I was going to go wander around the JY tomorrow toll i found one but if you can help me out that would be awesome.

Not sure about the size, but I'll be using a 2.0 or 1.9 SOHC Escort MAF.

What I'll do is 1st take readings at WOT at each RPM point from the VAF. Then, with the MAF plumbed inline with the VAF, take readings from the MAF at the same RPM points at WOT. That should give me both signal curves at identical airflow capacities. Then work up the translation.

[sketchman]

After some more digging, I'll now be using one of the newer style MAFs.
Part # ZL0113215. Easily available new on eBay and should be on lots of newer Mazdas, Toyotas, and others in yards so you can grab the sensor and pigtail.

MAF and IAT in one and readily available as a sans-housing replacement part cheap if ever the need for a replacement arises.

Looks like this....
$(KGrHqV,!ikFBIYpquTFBQUYOYn-FQ~~60_12.JPG
and pinout like this.

[Chobobulous]

What are you going to use for datalogging? That way you can adjust the voltage correctly. I don't think it is as liniar as you are thinking.

[sketchman]

^I think you're right. I thought about it a lot at work last night. I think what I'll have to do is get raw voltages at each RPM and then use that info and some number crunching to get airflow by voltage numbers.

"Datalogging" will be with a video camera and the multimeter fastened in front of the tach. Low tech, I know, but it's all I've got ATM.

[nitrofarm]

Anything happen with this? I would still like a MAF swap that's affordable. A MAF doesn't care how it's mounted. Upside down, turned however you like, and pointed literally however you need it, and once it's mounted, gravity and G-forces don't affect it. And then there's the looks thing and it being more compact.

So, bump for news.

Whats wrong with an Aspire ECM system ?

[sketchman]

^You have to swap the whole harness, and ECU, and for some of us, finding Aspire parts is tough.

[nitrofarm]

^You have to swap the whole harness, and ECU, and for some of us, finding Aspire parts is tough.

ECU yes,whole harness no you could reuse most of the Festy wiring if you didnt want to use the Aspire harness. Look how easy it is to convert an Aspire to VAF on the Aspire.com. when doing the BP swap. Your basically doing the same thing in reverse if you change a VAF to Mass Air. I cant recall his name but a member in Dallas is running a KIA Mass Air in his Festy. Its not like your going from Mazda to Honda. Its actually pretty easy,I've been looking for a rainy day to do this to my Festy. (Not a fan of the VAF system) Just thought I'd throw this out for you.You def have the skills to do this. You could draw it out on paper first and have it done in a weekend.

[sketchman]

Yeah, Donsvo or something like that. He's also got a BP too, though. I'd really rather leave as much as I can where it is to do it. I'd rather not pull the ECU or wiring, and this opens up other doors too, theoretically. When you have control of the MAF signal you can do whatever you want with it. Add in the ability to intelligently fool the ECU into thinking the O2 sensor is happy all the time, perhaps even the ability to read a wideband, and you have a tasty recipe.

This is as much a stepping stone to learn with as it is getting rid of an annoying item in my engine bay. Probably more so.

[sketchman]

Think I just realized I've been slightly stupid here.

Airflow doesn't follow the RPM speed. It follows the torque curve. Duh, right? So of course the signal curve looks funny. That doesn't mean the voltage changes aren't linear per airflow change. And in fact, I found an OLD Toyota document that says exactly that. It is linear. SOOOO, it is now so stupid simple to do this (famous last words, I know), that I'm near positive I can do it without even datalogging a thing from either the MAF or the VAF. In fact, that's the route I'm gong to go first.

Hold tight.

EDIT: To clarify, it would follow the torque curve to a degree. I was oversimplifying it to make it more understandable.