HAC hacking

[joust]

A wise contributor on this forum wrote this.
"The High Altitude Compensator is a barometric pressure sensor. It is used in the calculation of mass air flow along with Karmann Vortex frequency and Intake Air Temperature inputs. Without a functional HAC, the car will run differently according to barometric pressure. It will run richer in low pressure conditions and leaner in high pressure conditions. The closed loop operation will compensate fuel trim to some extent. Spark advance is also pressure corrected but there is no "fallback" sensor to make up for the lack of correction without the HAC. Spark timing is advanced inversely to barometric pressure.
The corrections made on account of the HAC sensor are small under normal conditions. In extreme conditions, such as a hurricane or driving through a large mountian range, the corrections can be significant."

This sounds like a prime candidate way of "tuning"
We can trick the ECU into thinking the barametric pressue is changing to change timing advance.
Anybody have any bright ideas?

 

[shaeff]

no, but im pretty sure i recognize that post as being drunk_medic's. haha.

perhaps you're on to something here... hopefully someone will chime in.

-shaeff

 

[Idealsupra]

i have a bright idea...STOP BEING SO FUCKING CHEAP!!!!!!!!!!!!!!!!!!!!!!!!!!

BUY A GOD DAMN 200 DOLLAR AFC AND TUNE WITH THAT....

UGH....

 

[mkIIIman089]

I don't think you can manually change timing advance with an SAFC... AFAIK.

 

[Idealsupra]

I don't think you can manually change timing advance with an SAFC... AFAIK.

the only thing youll accomplish by playing with the HAC sensor is fucking things up...BUT have fun...

 

[mkIIIman089]

Hey, I didn't say you should. I'm just saying that I thought it was more an e-manage thing. Not an SAFC.

 

[shaeff]

aaaaaaaannnd someone chimed in. lol

-shaeff

 

[Idealsupra]

aaaaaaaannnd someone chimed in. lol

-shaeff

:rofl: did you REALLY expect anything less from me?

 

[Idealsupra]

Hey, I didn't say you should. I'm just saying that I thought it was more an e-manage thing. Not an SAFC.

i agree...about the timing thing...BUT i was using an example....as in stop being cheap..the necessary mods and do it RIGHT...that is all...

you want timing advance? turn the CPS :momaru:

 

[IJ.]

Wouldn't any adjustment the HAC could make be in the wrong direction for performance? (ie: The higher in altitude the thinner the air the less fuel/timing)

 

[chevyeater]

I don't think it'd be worth the trouble, as the adjustments would be across the full RPM and load ranges and not significant until you get close to the limits of the sensor output. Ideal put it a bit more bluntly than I would have...

Wise contributor :icon_redf

 

[shaeff]

:rofl: did you REALLY expect anything less from me?

haha, no. in fact, thats almost exactly what i was expecting! and good advice it is!

-shaeff

 

[Idealsupra]

I don't think it'd be worth the trouble, as the adjustments would be across the full RPM and load ranges and not significant until you get close to the limits of the sensor output. Ideal put it a bit more bluntly than I would have...

Wise contributor :icon_redf

haha yeah well...

not only is chevy right about the adjustments it could make...BUT think of this also...lets say you trick it into another pressure...

the second the pressure changes from when you "tricked it" your settings would get screwed up...

 

[Shawndude]

The HAC has a range from way below sea level, to some stupid high mountain goat territory. At sea level it applies no correction.

Screwing around with it, it seems to work basically like the AFM input of sorts. As for timing, it doesn't seem to make a difference on it's own account, so it's probably programmed to adjust it in conjunction with other inputs, and not solely relying on this one sensor alone. You can fool it with the Maft unit if you want, and observe any changes. But since we don't have a timing monitoring system, not sure how you'll know what it's doing anyway.

However turning the CPS seems to get accepted by the ECU at face value, and it will not correct for it. So bumping back the timing a few degrees may be a good idea when fooling the AFM input with oversize meters.

 

[joust]

On the cheap part....i'm somewhat guilty.
I'm looking at either the E-manage or a MAP-ECU. I was hopeing that they could be used to manipulate the HAC signals to change the timeing advance/retard. If I were not cheap i'd go whole hog and buy a AEM and do it right.

I have thought about it. Inteligently fiddling with the HAC signals would require a minimum of a MCU with some glue logic and quite a lot of code, time and diagnostic tools not to mention either track or dyno testing.
Do you call that cheap? Obviously this will not be accomplished with a simple potentiometer or some such device. It would be a fun project. IMHO

Emanage:
does this have control lines that may be used in this sort of application?

 

[NegativeGeForce]

get a apexi timing controller...sure ur basicly tuning blind with it, but if your on a dyno you can play with slight timing numbers....its 200 bux for one and its much easier then hacking the hac and probably getting little or no gains