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Re: Device to monitor ECU signals to BPC Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 11 Sep 2009 13:44:00
In Reply to: Device to monitor ECU signals to BPC, sam96CS  [Profile/Gallery]
, Fri, 11 Sep 2009 08:22:58
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The BPC consists of two coils, with a common wire (the third line, pin 2, tied to 12 volts. The ECU has two transistor switches, one for each coil wire, that switches the coils to ground.
The ECU grounds one coil, then the other. Only one coil is grounded at a time. It grounds the coils as pulses, 90 Hz below 2500 rpm, 70 Hz above 2500 rpm.
The width of the pulses - how long they are grounded - determines the position of the valve. So if both coils are grounded the same amount of time, the valve is in the middle - ground one longer than the other, and the valve moves towards the more grounded side.
If Pin 2 of the ECU / Ping 3 of the BPC is grounded longer than Pin 26 of the ECU/Pin 1 of the BPC, the boost pressure is Reduced. If Pin 26 ECU/Pin 1 is grounded longer, boost pressure Increases.
Other things to note - the normal coil resistance is 3 ohms, so the ECU is sinking around 4 amps of current per coil - assume 12 volts after transistor drop, 12/3=4.
Also - anything flickering faster than 10 Hz looks to be on solid. At 70 Hz, you won't see flicker.
SO- you could go out and buy a simple red/green LED (as an example, Radio Shack 276-012) and a current limiting resistor - say 600 to 1K ohm, 1/4 watt, and wire them in series. The LED consists of two LEDs - a red one and a green one, tied 'backwards' in parallel. When you put voltage across the two pins one way, you get Red. Reverse the polarity, it glows green.
Say you figure out that putting 12volts on pin A of the LED and ground on Pin B makes it glow red. Simply hook Pin A to ECU Pin 2/ BPC pin 3, hook Pin B to the resistor, and the other leg of the resistor to ECU Pin 26/PBC pin 1.
Say the ECU grounds pin 26 (BPC pin 1). That will ground B of the LED. Pin A of the LED will be at 12 volts, because it can pull current through the ungrounded coil attached to 12 volts.
When both coils are being pulsed the same amount, both LEDs will both turn on for the same amount of time. Red and Green will combine, and you'll see Yellow.
When the coil attached to ECU 26/BPC 1 is grounded longer (more boost), the Red LED will be on more of the time, and the color will get redder. Less boost, and the LED will be more green, on average.
This is cheap and dirty - the color swing won't be huge. There are ways to amplify the pulse width differences, but it'll take more circuitry than $2 worth of parts, but it'll work, and won't hurt anything.
Why won't it hurt anything? With the 600 to 1K current limiting resistor, the LED will pull between 12 and 20 milliamps. Remember, the ECU normally sinks 4 amps, which is 200 times the LED current. It won't miss anything. And yes, the LED will pull some current through the coil that is supposed to be off, but again, about 200 times less than the coil normally sees. No big whoop.
See - that's what 4 years of college, 2 years post-grad, and 30+ years designing advanced aerospace equipment will get you - a resistor and a LED. Mom would be so proud!
posted by 76.211.18...
, Fri, 11 Sep 2009 08:22:58, Fri, 11 Sep 2009 13:44:00 <-- Viewing This Message, Sun, 13 Sep 2009 16:27:17, Fri, 11 Sep 2009 11:13:12, Fri, 11 Sep 2009 15:30:44, Fri, 11 Sep 2009 13:10:17
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