BigMouse

Hey there, been a while, but I've been doing some thinking of how to make my car more awesome.

I came up with the idea of building my own electronic boost control. Here's the concept:

- ECU for the 3B has a signal output for the stock boost gauge on the 200tq dash.

- This output is run directly off the internal pressure sensor in the ECU.

- I think I've figured out a way to utilize this signal to make my own electronic boost control, a very simple design too.

First, some R&D. Drew out what I wanted to do and how I could make it work. Then hooked up a multimeter to the signal and measured the voltages at various boost levels (0, 7psi, 12psi).

<img src="http://twigmouse.ipupdater.com/audistuff/multimeter.jpg">
(Yes, I am over 200,000 miles now)

As you can see, the voltage with the boost at zero (engine off) read 2.42v. I drove the car around (with the wastegate valve disconnected to regulate at 7psi, then with it connected to regulate at 12psi). I took a few readings each time, averaged them, and got the following results:

0psi = 2.24v
7psi = 3.57v
12psi = 4.50v

Did some math, came out with an average voltage gain per psi of .17v. Used this result to calculate what the voltage would read at 15psi (my goal) and got 4.75v (a bit lower to allow for error).

My plan, to build a circuit that opens the wastegate valve when the input voltage hits 4.75v. To do this, I bought a small relay that triggers at 3.5v on the relay coil. Run a resistor in series betweent the relay coil and the ECU signal that drops the voltage to 3.5v output at 4.75v input. This (I hope) will cause the relay to trip when the input voltage reaches 4.75v (boost at 15psi). The rise and drop in pressure will regulate itself at the level under WOT.

<img src="http://twigmouse.ipupdater.com/audistuff/boostcontrol1.jpg">

Above you can see the unit so far. I have not aquired a potentiometer yet, but will do so tomorrow, and hopefully have it running by then as well. The pot will be installed between the green wires. What do you all think?

pro_mtn_biker

nice man, good work, let us know how things work!

Brdman*

try a variable resistor, so you can dial it in exactly

|skolnick

Good idea.

|skolnick

<ul><li><a href="http://www.urs4.com/technical/engine/UrS4_boost_controllers.html">Although your solution gets it done on a tight budget!</a></li></ul>

YumyJager

Cool idea, but I thought hte boost guage's reading was laggy?

cuatrokoop

That is why I am going mechanical. Good electronic (analog) gauges are better than mech. however.

pro_mtn_biker

note how he says he hasn't aquired a potentiemeter yet

BigMouse

Yup, read that long ago. But I wanna get this done for under $20

BigMouse

The gauge is laggy, yes, the signal is real time however.