Relay Board mod: 2-wire PWM Air Valve + electric fan relay.

[Hardwyre]

Hey Hybrid. I thought I might share this and see what you all thought.

 

'76 280Z.

MS2-extra on a v3.0 board.

 

I have a 2-wire Bosch PWM air valve (0-280-140-516) that I intend to use for idle air control. The Z is also equipped with an electric radiator fan.

 

In an attempt to clean up the engine bay, I figured if I can run the fan straight from the MS module, I could eliminate a few extra pieces in the engine bay; mainly the thermal switch (which the previous owner poked between the radiator fins), the fuse, and the relay.

 

Talking with DIYAutotune, one of the easiest ways to get a fan is to just use one of the IAC outputs as a spare since I'm not going to be running a stepper motor. IAC 1a sources +12v on pin 25 if you added the IAC jumpers on the bottom of the 3.0 board per these instructions: My linkhttp://www.megamanual.com/ms2/IAC.htm

 

Well, when running a PWM valve, on the relay board you remove the relay and jumper the 85 and 87 pins on the socket, resulting in a direct connection.

 

Well, I would have to run a relay inline for the electric fan, why not just use this "empty" spot on the board instead?

 

Looking at the board, I'm thinking I properly tracked all the traces. And this is what I came up with:

 

After figuring the traces, I schem'd out this:

 

I'm suspecting the main fuse may not like the extra load from the fan, but we'll see. I'm thinking of placing a capacitor across the fan leads. I have a 35v/3300uf cap and a smaller 25v/1000uf. I wonder if either of those might be large enough to keep from having a big surge when the fan kicks on. Any ideas? Think I should just run a fifth fuse for the fan at the board wired directly to the 12V Batt pad?

 

Humm... just pulled some huge 200v/820uf caps, but the others would work better for capacity's sake.

 

I hope this works because I like the idea of having the relay on the board and one less piece of clutter in the engine bay.

Edited January 16, 2011 by Hardwyre

[zack_280]

<P>Nevermind. Now I see your dilemma and the solution looks solid.</P>

Edited January 22, 2011 by zack_280

[Hardwyre]

Couldn't you just reconfigure the FIdle (PM2) output in Megatune to go high when the coolant temp is over a set value (say 170) and use a hysteresis of 15 so it'll turn off at 155 or so? I am a Megasquirt newbie, but it seems to work on the JimStim board.

 

I have to use the FIDLE for my PWM air valve since I'm not knowledgeable enough to design its own circuit. The reason for the relay board mod is to move the IAC 1A over to where the FIDLE was, while bypassing the FIDLE past the relay. This way I get IAC 1A on the relay, and FIDLE is essentially jumpered. It lets me use what would otherwise be a jumped relay terminal for a fan relay. Keeps me from having to put another relay in the engine bay somewhere. A little cleaner on the wiring.

[zack_280]

Here is what you did. It works well and is pretty clean since you left the FIdle output on the same relay board terminal.

 

 

Here is another option that would take less wiring on the relay board, but swaps the IAC-1A and FIdle output. I did not buiild my relay board, so for me the less changes the better. I havent tried to swap the wires on the DB-37 and it may be easier to cut the traces and add two more jumpers on the relay board, but you get the idea.

[Hardwyre]

Here is what you did. It works well and is pretty clean since you left the FIdle output on the same relay board terminal.

 

 

Here is another option that would take less wiring on the relay board, but swaps the IAC-1A and FIdle output. I did not buiild my relay board, so for me the less changes the better. I havent tried to swap the wires on the DB-37 and it may be easier to cut the traces and add two more jumpers on the relay board, but you get the idea.

Wow, very well done. Took me a moment to realize what I was looking at, but yes, I can see exactly what you're talking about.

 

You're correct that it did require some wiring, but I liked the idea of keeping the changes to one piece of the puzzle (in this case the relay board) vs. having it spread over a couple of parts. I had actually considered swapping pins, but I refuse to crack open the cable harness since it took me forever and a day to make the stupid thing. Also, if I decide to switch things in the future, I can remove the board, and make changes at the comfort of my desk instead of trying to solder the harness in the engine bay (I'm assuming there's going to be much fun involved in trying to get it through the firewall.)

 

Also, thank you for confirming my layout. DiyAutoTune gave me the okay on the changes, but it's nice having the confirmation from multiple eyes.

[zack_280]

I didn't have too much trouble getting it through the firewall. Just had to remove the connector housing and bend it sideways and it went right through. I'm still at least a month from getting it running, though.