Is transistor change always needed for PWM idle

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ihenter
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Is transistor change always needed for PWM idle

Post by ihenter »

I want to use pwm idle with the BAC valve on my RX-7. The resistance of the valve is around 10 ohms (about 10x the ford one according to the write up) so i'd imagine the current would be a 1/10th so you wouldn't need to change the transistor.

I know a lot of people have done this so i'm curious if you just left it or changed the transistor.

Thanks
-Ian
jsmcortina
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Post by jsmcortina »

Actually that sounds about the same as the Ford one. Either way, this is still more current than the standard transistor can handle, so do the upgrade.

James
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Scummer
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Post by Scummer »

The Ford/Mazda valve is also 10Ohm. I run the standard V3.0 idle circuit with a 10Ohm/10Watt resistor in series to keep the current down under 1Amp and it has been idling perfect since 4 month.

I say Mazda valve, because the Ford Probe runs a Mazda KL03 engine.
'96 Probe GT - MS2extra 2.0.1, MS V3.0, VB921's, coilpacks, 6-1 wheel, 580ccm injectors
'69 Mercury Cougar Convertible 351W - MS V2.2 carb to FI in progress
ihenter
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Post by ihenter »

thanks scummer, that definatly sounds like the simplest solution.

wait, will this also work with a v2.2 board. It should as long as the resistor limits the current through the transistor (ie through the valve) to under .8 amps, right?
Scummer
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Post by Scummer »

ihenter wrote:thanks scummer, that definatly sounds like the simplest solution.

wait, will this also work with a v2.2 board. It should as long as the resistor limits the current through the transistor (ie through the valve) to under .8 amps, right?
And that it should. 10R from the resistor and 10R from the valve coil in series is 20R and should keep the amps to under 0.8A.
Take a look at the trans thats used in the V3.0 board since I've been running the unmodified idle circuit from the V3 board with the 10R resistor for month with great success.

Initially I just wanted to minimize the amps through the valve coil to avoid overheating the coil, but at the same time it also made the valve less noiser at 250Hz duty cycle. The stock ECU was running the valve at +5V with 250Hz.

Thomas
'96 Probe GT - MS2extra 2.0.1, MS V3.0, VB921's, coilpacks, 6-1 wheel, 580ccm injectors
'69 Mercury Cougar Convertible 351W - MS V2.2 carb to FI in progress
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