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Old 04-29-2012, 05:20 PM   #1
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Default DIYPNP MS1 and the fuel pump

Hey there!

I'm installing a DIYPNP unit, the MS1 version, into my car. This was a unit that was built for a 90-93 (like mine) around 2009, by Braineack from the forums here.

Despite some small customizations I'm doing on the install, I'm following most of the instructions that I was given (and that the previous owner was given by Brain), and they say that if you're a 1.6 owner, you must wire a small shunt between F/P and GND, in your diagnostics plug. This was on Brain's instructions. However, reading the instructions on legacy (MS1) MSPNP from the diyautotune.com website, they say that the ST_SIGN 10 amp fuse should be removed... So, my question is...

Can I remove the fuse instead of jumping the diagnostics connector? Does it do the same thing?
Should I do both things? (unlikely since removing the fuse wasn't in the original instructions).

The only reason I ask is because I feel a lot safer removing that fuse than wiring the diagnostics box and having the small shunt fail me at a later point.


Also, just for curiosity... What does removing the fuse do? And what does the F/P to ground jumper do?


If anyone could help me with this, I'd be greatly appreciated!
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Old 04-29-2012, 08:04 PM   #2
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If its an older unit I built you don't have to remove that fuse.

Typically the afm grounds the fuel pump. Siince we tend to remove it wiith an ms install you have to jump it by altenative methods.

F/p gnd is an older sub par way.

Id perfer if u ran purple wire under dash to the fuel pump relay and spliced into the lt green wire.


The msps backfeeds 12v through the relay and runs it...this is the same way ithe stock ecu primes the pump.without pulling the fuse however it overloads the driver In the mspps and burns up.
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Old 04-29-2012, 08:07 PM   #3
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Thanks, but what about the jumper between F/P and GND... What does it do? Doesn't it do the same as removing the fuse (cutting the power to the fuel pump relay I think)?
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Old 04-29-2012, 08:36 PM   #4
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It turns on the fuel pump relay
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Old 04-29-2012, 08:41 PM   #5
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Hmm, I see. So, my fuel pump will be running from the time I turn on my ignition? Or will the MS still control it?

EDIT: Nevermind, I understand now. It's only there as a means to provide grounding to the Fuel Pump.
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Old 04-30-2012, 03:21 PM   #6
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Well, I've wired the Megasquirt and everything following the instructions, but I seem to have run into a problem... My MS won't connect to the computer!

When I turn the key to the ignition position, the LEDs on the Megasquirt turn on except the middle one, and the fuel pump starts running and never stops. The COM port is setup on the computer as COM29 (using the USB adapter from DIYAutoTune), but I can't get Megatune to communicate with the Megasquirt... On the communications settings, I choose COM29 and 9600 baud rate, but nothing happens...

Is this how it normally should behave (regarding the fuel pump and LEDs)? What can I do to fix the communication issue?
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Old 04-30-2012, 03:24 PM   #7
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dont use megatune.

use tunerstudio.


reconfigure your com port to something between 1-5. I didnt think you could select higher than that.


outer LEDs should light up, middle is probably set to warmup depending on your loaded map. the fuel pump will always run as it is statically jumped with f/p and ground.
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Old 04-30-2012, 03:42 PM   #8
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Strange... The software does allow selecting the COM29 as COM Port though. I'ma give it a go with TunerStudio and see how it fares!

Thanks Brain
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Old 04-30-2012, 04:16 PM   #9
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F*** yeah it's running

Using portCheck provided some help!

Now I only need to set up the sensors properly. If any of you guys know EasyTherm5 and want to give me a hand, follow up on this topic:

https://www.miataturbo.net/megasquirt-18/using-easytherm5-hr_10g-65511/

Cheers and thank you so much Brain!
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