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Discussion Starter #1
Does it know if you are pushing the gas just a little, or going WOT? What part measures this if so?

I really need to know this (either question if you are sure)

thanks
 
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Discussion Starter #2
I think it's just a MAP sensor w/ electronics to give a MAF signal.
 
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Discussion Starter #3
Slasher48 said:
I think it's just a MAP sensor w/ electronics to give a MAF signal.
but does it give it a different signal if you are low throttle compared to high throttle?
 
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Discussion Starter #4 (Edited)
Depends on the intake manifold pressure (vacuum or boost). I'm pretty sure it's only a pressure sensor and eliminates a few other sensors (that were on the MAS) and gives a constant signal for those.

The throttle position sensor would give an indication of low or high throttle if that's what you need.
 
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I'm just wondering if there is something wrong with mine because it doesn't seem to be able to tell the difference, so is impossible to tune for both cruising and WOT. If it cannot do it itself (along with the old style SAFC, which I know cannot do it), then I guess I'm just going to have to get a new SAFC, which has a low and high throttle sensor that you can set different fuel flows for.
 

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you would have to get an afc..the vpc just changes your cars way of metering air..instead of reading mass air flow, it uses speed density or manifold air pressure, so to fine tune it you still need a gcc or afc..hope that helps
 

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The ECU will change whatever you tune in for low throttle fuel trim anyway. Why are you trying to change the low throttle map? The ECU uses the O2 sensor feedback to calculate the amount of fuel needed unless you are WOT..
 

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Ideal Gas Law

The VPC and speed density air measurement use the principle of the Ideal Gas Law. PV=nRT. Where P is in absolute pressure as measured from the MAP sensor. T is measured by the temp sensor and R is the Universal Gas constand for air. The Volume or in a time based unit of volumetric flow rate is determined by the engines displacement and volumetric efficiency. On a 3.0 L engine every other RPM the engine takes in to the cylinders 3.0L of air volume * (volumetric efficiency). Volumetric efficiency is about .85 to 1 in high performance engines. Because this amount of air comes in every other RPM (i.e. RPM / 2) the VPC needs also an RPM measurement. Substituting all the knowns in the equation. If you have the three inputs RPM, MAP and temp. The mass flow rate, n can be calculated. This is converted into a 0v- 5v output via the microprocessor in the VPC and sent out to the ECU.

That is how the system works.

Brian
 

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sonik said:
you would have to get an afc..the vpc just changes your cars way of metering air..instead of reading mass air flow, it uses speed density or manifold air pressure, so to fine tune it you still need a gcc or afc..hope that helps
anyway..

The ECU has two "modes" if you will, partial throttle and WOT. Under partial throttle, the ECU uses the O2 for the a/f ratio. It calculates the ratio based upon the feedback and goes from there. At WOT, it looks to it's MAF sensor. Depending on the MAF's value, the computer goes to a look up table and supplies the corresponding amount of fuel. (It also checks to make sure the O2 and MAF are within 10% tollerance)

The VPC gives the computer a changed MAF single which basically tricks the ECU into a different duty cycle. This is why the VPC/GCC/AFC/Whatever will not change anything other than WOT. (Technically, it does change basline idling stuff for larger injectors, but for all intensive purposes you can tune off throttle response)
 
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