MegaSquirt PNP2 Outputs

CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
20
13
33
Beaumont, Ab
So I've recently installed a MegaSquirt PNP2 in my '89 Fox and so far I love it. I love learning and tuning it myself. Already feels much better than it did with the A9L with a tuned SCT. I run dual Contour cooling fans which draw a lot of amperage on startup so I wired them into the MS separately. I wired them into output 1 and output 2 which are pins 24 and 25 on the options port. This supplies a ground signal when enabled.

My question is what can I use to turn my water pump on and off? I don't like my water pump running with key on engine off as it draws about 10amps so it's a battery killer if not planning on starting the engine. Also don't like the extra amp draw during cranking. I'd like to have my water pump come on after startup if possible. Has anyone done this? What wire can I use on the options port? Is it a ground or positive signal?

Under the Boost/Advanced tab and programmable on/off outputs I have FIDLE, Tach Out, Injector C, Injector D, Boost. Can I use one of those?

Thanks in advance for any help or guidance.
IMG_5445.JPG
IMG_5446.JPG
 
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a91what

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Mod Dude
Apr 6, 2011
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Fiddle is being used already for the idle valve.
Tach out is capable of pulling a relay in to power the water pump. Dont forget to place a flyback diode across the fan and water pump wiring to help increase the life span of both the relays and the motors. If you need part numbers I can supply that information.

I run a mark8 fan off one output (90amp initial draw) and dont have idle issues. I assume this is why you wired the fans separately?
 

CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
20
13
33
Beaumont, Ab
Fiddle is being used already for the idle valve.
Tach out is capable of pulling a relay in to power the water pump. Dont forget to place a flyback diode across the fan and water pump wiring to help increase the life span of both the relays and the motors. If you need part numbers I can supply that information.

I run a mark8 fan off one output (90amp initial draw) and dont have idle issues. I assume this is why you wired the fans separately?
So I can use Tach out to turn my water pump on? Which pin number is that on the options port? Is that a positive or a negative signal? I'm not 100% sure what you mean by the diodes across the wiring.

Yes the reason I run them separately coming on at different temperatures is because both together draw well over 100 amps initially and obviously my idle drops. I haven't fully figured out all of the settings for a good solid idle as I'm still learning and tweaking.
 

a91what

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Tach is pin4. And the output should be low (ground) so you would wire the relay with switched 12v to pin 86 and ground the relay pin 85 with the tach output.

It's common to use a flyback diode across motor loads, when you shut the load down abruptly it will create a voltage spike. This can exceed 100v in some instances so to stop that from damaging electronics on the 12v system a flyback diode is used. They are installed internally on the ECU to protect it but that does not protect the motors or relays.

As an example the ac clutch has a flyback diode.
 

Blown88GT

Founding Member
Nov 13, 1999
2,110
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Palm Beach Gardens, FL
Looks like this.
iac diode.jpg


Used here & other places.
EVTM_p032_cr.jpg


Here's one across the fan motor. Must be connected "in reverse", cathode to positive, anode to negative.

FanControl.jpg

Not needed if you use a PWM controller.
IMG_1676.JPG

IMG_1691.JPG
 

a91what

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Apr 6, 2011
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I just build my own fan controllers, MS3 is capable of pwm control for a fan so i utilize an SSR to control the fan with closed loop temperature control. of course i use diodes on both the control and load side of the SSR with a large heat sink as well.
 
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