Adding Boost Control To Your Power Fc - * The Cheap Ass * Method!

[GTRNUR]

Disclaimer

Starting off with the usual disclaimers, no guarantees, and of course im not responsible for your stuff ups etc. If you frequently burn yourself with a soldering iron then this isn’t for you. But if your capable of assembling a basic dick smith kit, then you can easily do this.

Background

So I initially wanted to add boost logging capability to my Power FC. Sure enough I happened to have a generic GM/Haltech 3 Bar map sensor in my stash of left over EFI parts from my various projects over the years.

A little research and I found PaulR33’s Power FC FAQ/documentation on connecting the sensor to your FC so you can do the logging. Along with this information was the data for correcting the scale and offset when using sensors other than the common Apexi sensors. This was all well and good unless your Power FC doesn’t support the PIM Scale/Offset settings that need to be tweaked in order to make a non standard MAP sensor calibrated to the FC’s vac/boost scales.

This was the case with the GM 3 bar sensor, so what I came up with is two circuits that can be used to correct the offset, or the scale and offset of the FC’s boost input. This allows the use of cheap and common sensors to interface properly for logging or boost control.

(circuit diagrams are attached)

Circuit 1

This circuit uses a 7805 (very cheap and common voltage regulation IC) and a 1N5004 diode (also cheap), to make a 5 volt regulated power supply for the MAP sensor. The diode is used to offset the sensor ground voltage by 0.6V, so that the inaccuracy is corrected. This calibrated the GM 3 Bar map sensor to the FC accurately, and presented an offset inaccuracy of 0.05kg/cm. The scales of the GM sensor and the normally used Apexi sensor must be pretty close (though I only tested to 1 bar).

This cost me $1.90 in parts, plus the sensor and heat shrink I already had. I assembled the whole circuit mounted off the 7805 IC, and then wrapped the whole lot in heat shrink. The IC does not need to be mounted on a heat sync as the map sensor will not draw more than about 50-75mA. The circuit can do 150mA before the component needs the be thermally mounted.

Circuit 2

This circuit is a variation on circuit 1, using a LM317T variable output IC. Same principal apples for offsetting the voltage, but a 2K carbon variable resistor is used to allow the voltage on the MAP sensor to be under or over driven. Under driving the sensor will allow the hand controller to display a lower boost level, over driving it, the opposite.

EXTREME CARE MUST BE TAKEN IF YOU DO THIS… or you will let the smoke out of your map sensor, and potentially damage the FC map sensor input, or even toast your ECU completely. I would not over drive the sensor by more than 6v if it is an electronic type sensor (like the GM sensors). Also, take into consideration the boost levels you are running.

Running to 1.5 bar on a 3 bar sensor means the output voltage of the sensor will be about 4 volts, and is still very safe for the ecu.

Running the same boost level on a 5 bar sensor will have a much lower output voltage, as the sensors internal diaphram will me moving less for the given pressure. Also, running a 5 bar sensor if you only plan to run 1.5 bar is not a good idea, because while you can correct the scale and offset error with the circuits, the 5 bar sensor will give you less resolution (accuracy) than the 3 bar would.

TESTING

How the circuits work?

Simple. The regulator IC’s provide a constant 5 volt (or corrected 5V for the LM317 circuit), with an offset ground signal. By using the 0.6 voltage drop or 0.3 voltage drop of common diodes you can offset the sensor’s output voltage. This corrected voltage is then used by the Power FC to produce and display the correct boost/vac levels.

Using no diodes would be the same as running the sensor off the regulated power that is suppled from the MAP sensor plug on the ECU.

Using a single BAT46 diode corrects by 0.3 volts.

Using a single 1N5004 diode corrects by 0.6 volts.

Running the diodes in series would correct by 0.9V etc…

So this takes care of the input side of the boost control. Then you just need to score a 3 port solenoid for the output side. You can source these from anyone selling boost control solenoids in Australia. They are all the same. Haltech, vipec, wolf etc. Ive seen them being sold on ebay too very cheaply.

Thanks to Paul and his FC manual for getting me started on this.

Enjoy!

Cheers,

Ian

Edited March 23, 2010 by GTRNUR