DIY A/F controller and/or guage...

[uRiDiAN]

ok. first off, the controller. i know someone who owns a neon that made his own AFC in a manner very similar to what we'd do for the IAT/ECT potentiometer. he ran these along with some circuitry (i don't know specifics) to the MAP sensor (Manifold Air Pressure). what these did was fool the ECU into thinking there was more or less pressure in the manifold, thus ECU changes fuel mixture accordingly. what i'm wondering is if it would be possible for us to do anything similar with the MAF sensor or anything else? i know the MAF is harder to "fool" than the MAP sensor, but the theory should be about the same.

now if we could, that would be all fine well and good, but we'd need an A/F ratio guage to tune the thing. i'm wondering if you can wire something like this up with radio shack parts... ya know, colored leds and what not. i mean, it's basically measuring the voltage being registered on the O2 sensor, correct? how hard could it possibly be?

this is just my attempt to continue work on my car, even when i'm really broke... :) but i'm sure everyone would be pleased to spend $30-40 for both rather than $300 or so for both...

uRiDiAN

[PuckPuck]

so basically you are saying create your own MAF Optimiser..... me likes.... i "may" give it a try.......

[FastCougar]

better have a handy 2nd MAF ready. Better yet, get an 70+mm MAF from a late model Mustang and work on that for the optimizer. However, since this would require splicing the MAF harness, it isn't a great idea unless you are an electrical engineer or know what you are doing. Not to mention, it will be very obvious to anyone working on your car at the dealership ... better not take it in complaining about idle problems or backfire at WOT.

[uRiDiAN]

that's a good idea... i wonder how much i could get one for at a junk yard. did all the mustangs have that MAF? or just GT's?

plus, my warranty has been up for a while now...

uRiDiAN

[exigent]

im not 100% certain on this... but i do think that it is NOT economical to make your own a/f gauge. Reason is... the voltage is SO low already.. that almost any "tapping" will result in a skewed reading going to the EEC. Actual a/f gauges have the electronics nesasary to compensate for this.

With regard to the a/f controler... sure... some resistors would work... but now how do you set the specific resistence at any one rpm. Not a super complex circuit... but definatly not somthing you can build if youve never done REAL electronics work... im talking etching your own pcb's and whatnot. A simple resistor on the signal wire will get the reading slightly higher or lower for ALL rpms. Ive seriously thought of doing this to compensate for the 19lb/hr injectors... but i dont have a spare maf and or eec laying around in case i make a mistake... remember.. the eec is a bit fragile. So is the maf.

[Frank]

The other thing you have to figure is that the MAF voltage is not directly proportional to CFM. Because of this, the resistor will have a much greater effect at high-rpms than at low-rpms.

I'm not sure if I'm ever going to experiment with this myself, but this data should give you a better idea of how the MAF voltage changes with different amounts of air...

http://www.pro-flow.com/19flow.htm

Also, this explains how a real MAF optimizer works:

http://www.vetteguru.com/mods/howto/

[DemonSVT]

Great idea.

Extremely steep learning curve!

One screw up and your PCM is toast. (voltage spike!)

One screw up and your engine is toast. (lean mixture!)

Be very careful... Make sure you have access to the PCM's specs as well as the Factory Manuals

[RicciHull]

Since I'm an EE I'll chime in here.

Making your own AF gauge would be tricky. I bet most of the current designs are a high resistance voltage probe, much like a multimeter. From there it is probably fed through a small linear amp (op amp maybe), then displayed. (bar graph, ratio, millivolts)

As for the MAF, this is a little more tricky. You would need to know what each signal means coming off the harness, what its range of values is too. You would need a high quality POT that wouldn't turn a few degrees when you hit a bump.

Like DemonSVT said, there is alot at risk here, the PCM, engine, MAF... I would rather pay for a pre-engineered one.

[uRiDiAN]

well i can understand the controller being scary, and i hadn't really put too much thought into that aspect of it, but at least the guage wouldn't be as dangerous, i'd think. plus, it would be neat to incorporate the guage into the dash (i have spots ready for extra stuff) rather than a pod stuck in there. if someone will help with me what type of components i'd need for the guage (such as the components you discussed, ricci), i'd do that myself, seeing as the O2 sensor wires are already spliced and have MIL eliminators in there.

uRiDiAN

***edit***
better yet, since i'm sure you prolly don't want to tutor my ass about stuff, just point me towards a resource i can use to learn myself, that would be just as good
***edit***

[RicciHull]

If you insist on doing it yourself, I would get a small digital millivolt gauge, like an industrial panal mount one to use for the A/F gauge.

Just buy the cyberdyne. Its under 100 bucks I think.

[NorCalCoug]

Use lots of relays! Relays rock!!!! :)

[exigent]

an actual a/f gauge is only 40.00 or so.