Fuel pump outputting voltage when not on...

[rithsleeper]

I figured out the MS3 grounds the fuel pump wire and doesn't send 12v like my stock ECU did, so I will be swapping some wires to make that work. However before I made the connection I plugged up my JimStim to test the fp pin and found that when the RPM's were at 0 the FP pin was putting out ~4v? Then when I turned on the RPM pot it would be a ground/0V.

I don't see how this would matter seeing how the relay wont be triggered with that but just wondering if there is a short on my board? The car ran with residual pressure in the lines for all ove 3 seconds then stalled so I think everything else is working properly. This was the first start up though...

Thank you for any insight you can give.

[dontz125]

With the FPR off, you should have 12v (VBatt, really) all the way from the relay coil pins to the transistor pin. No current, no voltage drop.

Next point - the FPR circuit is meant to drive a relay, not the pump itself. Even little bike pumps draw too much current for the V3.0 transistor.

[slow_hemi6]

The ~4v is probably just there from the stims led indicator for fuel pump waiting to be turned on by grounding.

[rithsleeper]

Ah that makes a lot of sense. Ok. No worries. I'm sure it will work when I get home today. I'll just jumper the main power wire to the switch portion.