How to Read/Check VF Signal?

[Turbo Habanero]

So do you only check the VF reading at idle with a Voltage Meter sorry i might be alittle slow having trouble understanding how you get a VF reading for tuning purposes.

Is there some type of gauge for this? whats the best way to do this while driving

i understand the concept of it. Just don't know how to get the actual reading..:dunno:

Just slap me now:slap: cause im sure its something dumb im missing or looking over.

 

[jetjock]

Just connect a meter to it. Preferably one that can record max, min, and average values. Handy for determining what the system is doing and verifiying there aren't any vacuum leaks.

Either have to pick up the signal at the ECU or run wires in from the diag box. My car had a test panel and diag switch in the glove box for such purposes. There's also the data logger approach...

 

[Turbo Habanero]

ok thanks JetJock

so just hook up a volt meter to the VF wire and watch it from there?

Im assuming to just turn to the TSRM to figure out witch is the VF signal

 

[GrimJack]

That's exactly it, and there are only a few readings...

from memory:
0 = open loop
close to zero = lowest
close to 1.25 = low
close to 2.5 = middle
close to 3.75 = high
close to 5 = highest

The reading will bounce around quite a bit, but if you can graph the results it's pretty obvious what you're seeing.

 

[Turbo Habanero]

O is lean 5 is rich correct grim?

 

[GrimJack]

No, it's the other way around... and really, lean / rich is the wrong way to think about it. Think about it in terms of adding or removing fuel instead, as there is a critical difference, in that it's possible for the ECU to be adding fuel even when the engine is actually already rich, due to sensor faults, faulty fuel components, or bits that have been upgraded to flow more fuel, among other things.

Vf voltage / Fuel adjustment

0v / Reducing lots of fuel from base maps
1.25v / Reducing some fuel from base maps
2.5v / No change from base maps
3.75v / Adding little bit of fuel from base maps
5v / Adding lots of fuel from base maps

 

[Turbo Habanero]

ok will do thanks

 

[Dan_Gyoba]

'nother note, there's no point in checking at idle, since idle is always open loop mode. Similarly there's no point at WOT, since that's also open loop mode.

I made a bunch of Vf meters based on Jeff M's design from way back in the day. I think that I still have a couple left. They could use a bit of a design update, but they make for some interesting blinky lights to watch while driving. Eventually, (while in closed loop mode) the ECU will learn so that the Vf voltage will stay at the 2.5V range, as the ECU learns and adjusts the base maps to match your car and environment.

 

[jetjock]

^ That's just bad info all around...