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Using DBW signal to operate cowl induction

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68RSSS

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I have a new fuel injected engine in a 68 Camaro with a 69 Camaro cowl induction hood with a flapper that would normally open from throttle pedal linkage that would send a signal to a solenoid that would open the flapper. The new engine has drive by wire so there is no linkage to operate the flapper. The flapper has a solenoid that opens and shuts it. I know the DBW signal ranges from .5 volts to 5 volts depending on pedal position (.5 volts at idle to 5 volts with the pedal floored). I want to somehow get the flapper to open with just a little throttle pressure so I figure somewhere around 1 volt would be a little off idle. Is there a way to get this solenoid to open the flapper at the 1 volt signal and shut the flapper when the signal is below 1 volt?
 

MikeMl

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Most Helpful Member
Yes, an opamp or comparitor IC, a Zener, a few resistors and capacitors. Can you wire it if we send you a schematic?
 

68RSSS

New Member
Thanks. I can wire and I can solder as I did my whole car myself. Unfortunately my knowledge of the componets you listed and the ability to build from scratch would be lacking compared to the knowledgeable people on this site. However after bringing this up to many people this is the first place that says its possible. Therefore I would love to see a schematic as it would at least be a start for me. I admit I was hoping it would be easy but as usual nothing is ever that easy. I will take any info I can get. Much appreciated
 

MikeMl

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Most Helpful Member
Please answer these questions:

1. How much current does it take to run the flapper?

2. Does the flapper use a reversing DC motor with limit switches (like an electric power window), or does it draw current the entire time the flapper is open, and a spring pulls it closed when you shut off the current?

3. Does the flapper have its own relay?

4. If you need to add a relay, could you use a typical automotive 12V 30A sugar-cube relay?

5. Can you tap into a "key switched" 12-14V source that can supply the relay coil current?

6. Can you tap into the "DBW" signal easily?
 

68RSSS

New Member
I’ll do my best.
Hopefully this answers the first three questions to start. The solenoid requires 12 volts. From what I can find out, the original system used a pushbutton switch on the linkage. When floored the button would bottom out on the firewall of the car. When bottomed out it sent a signal from this switch to a relay, which then went to the solenoid.
When 12 volts is applied to the solenoid the plunger extends which opens the flapper and stays extended until the 12 volts is cut, then the plunger recedes and the flapper closes.
So to answer the first three questions in short, 12 volts, draws current the entire time flapper is open, and yes the original system did use a relay.
4. Yes I could add a relay. I have a few extra from automotive projects that I would just need to check the amps on, or buy one, but yes it can be added.
5. Yes I can easily get switched 12 volt signal to the relay
6. Yes I can tap into the DBW signal. Harness is somewhat accessible and I have a schematic for the complete harness so I know what wires are giving the .5 to 5v signal.
Thank you for the assistance
 

MikeMl

Well-Known Member
Most Helpful Member
Ok, here is my hack at it. You will need to build the part inside the dot-dash box as a small shielded module, like in an Altoids tin. There are four connections to the outside, dbw, Pwr (switched 12Vdc via the Ignition Switch), rly (to 12V relay coil), and Gnd.

The circuit has a high input impedance, so should not load the dbw signal. A 1 MegΩ TrimPot (U3) is used to set the trip level, which can be adjusted from about 1V to about 4V. The circuit has about 10% hysteresis (drop-out voltage lower than cut-in voltage) to prevent chatter. U1 is a 8pin minidip version of the LM555C timer chip.

The relay U2 can be one of the automotive 12v "Bosch" type, with a normally-open contact. Note that the power to the circuit should come from the key-switched 12V. The power to the flapper should come separately from the main battery bus (not through the key switch), and should be fused as required as shown by X1.

Here is the schematic and simulation: The lower plot pane shows V(rly) switching as a function of V(dbw) and the pot setting at 0% (green) , 20%, 40%, ..., 100% (grey). The cursors show the cut-in 1.25V and cut-out 0.74V with the pot wiper set to the top pot terminal.
TPS.png
 

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68RSSS

New Member
Awesome. Will take me some time to wrap my head around and find the componets I need to build. I think I can do it though. Thank you for the responses. At least I know it can be done so that is good motivation. I will update when I can get this started. Thank you
 

MikeMl

Well-Known Member
Most Helpful Member
Digikey or Mouser is your friend.
 
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