2.1 dual vr conflicting with ms3 vr possibly?

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jsmaz3
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2.1 dual vr conflicting with ms3 vr possibly?

Post by jsmaz3 » Wed Nov 06, 2019 11:46 pm

So I've been chasing an issue i cant figure out with my ms3 3.57. i have a 2.1 dual vr board hooked up externally about 4 inches before the megasquirt. i have sheilded wires run to and from the board to the megasquirt, i have the pots adjusted in the megasquirt full counter clockwise and r56 pot turned clockwise 2.5 turns. itll start and run fine with no issue, but at 5k rpm the signal drops out. when i mess with the ms vr circuit it changes but i cant get it to either idle and rev past 5k. i was wondering if bypassing the ms vr circuit would help and how id do so if it would help.

jbelanger
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Re: 2.1 dual vr conflicting with ms3 vr possibly?

Post by jbelanger » Thu Nov 07, 2019 10:53 pm

Bypassing the MS on-board circuit is the normal way to install the dual VR board but this is als done with the board inside the case. Having the board outside the case means that this by passing is more risky.

You don't mention which wheel type you have as this has a significant impact on what could be the issue. One potential solution would be to use a shunt resistor: a 1k to 10k resistor between VR+ and VR-.

Jean
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jsmaz3
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Re: 2.1 dual vr conflicting with ms3 vr possibly?

Post by jsmaz3 » Fri Nov 08, 2019 3:13 pm

Sorry. I forgot to mention. It’s a Saturn it uses gm7x. I’ve moved the board inside the megasquirt and I’m now going to use the db15 for my vr input. This way I can route my wire away from the rest to reduce potential noise. But do you think a resistor across vr+ and - may help? Also I bought the 12v board and wanted to confirm that bridging the solder junction on the 2.1 board near the V+ makes it 5v by bypassing the voltage regulator circuit. And should I also maybe remove the components from the voltage regulator circuit or would leaving them there be fine.

jsmaz3
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Re: 2.1 dual vr conflicting with ms3 vr possibly?

Post by jsmaz3 » Fri Nov 08, 2019 3:16 pm

Also I haven’t powered the megasquirt or put it back in the car yet until I was sure of the power supply situation. And I’ve wired the out one to the 4 pin one the j1 header

jbelanger
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Re: 2.1 dual vr conflicting with ms3 vr possibly?

Post by jbelanger » Fri Nov 08, 2019 3:33 pm

You can still use the on-board voltage regulator even if the board is inside the MS case. Actually, I would recommend it since the components are there. Just use a 12V source on the MS board and you will still have a 5V output from the board.

With a pattern having such a small number of teeth, you shouldn't need the shunt resistor. But if you still have problems getting a high RPM signal, then it certainly something to try. The worse that will happen is that the signal will no longer be read at low RPM which is obviously not what you want but can be corrected by either removing the resistor or going with a higher value resistor.

The expected behaviour is that a low resistor value will help the high RPM signal but may hurt the low RPM signal while a high resistor value will not affect the low RPM signal but may not help the high RPM signal enough to get the full range. The recommended 1k to 10k resistor value range should give you something that will get you the full RPM range. Some rare setups may need to go down as low as 500 Ohm or as high as 20k but I would not go outside that.

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jsmaz3
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Re: 2.1 dual vr conflicting with ms3 vr possibly?

Post by jsmaz3 » Fri Nov 08, 2019 3:53 pm

Ok, I’ll try it without the shunt first and see what happens. I tried bypassing the megasquirts vr conditioner at first by using a jumper lead from js1 pin 2 to j1 pin 4 and it didn’t pick up any signal that way. Someone had the megasquirt before I got it and had it set up for a Mitsubishi 4g63 and they had a wire soldered to pin 4 on j1. Not sure what they where using but there may just be an issue with the circuit on the megasquirt itself.

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