Wiring new fuel pump for carb conversion Options

[mb914]

Hi All,
I recently installed an engine with carburetors on a 2056. I am trying to use the stock FI wire to power the pump. I read where you need to jumper a cable from pin 30 to 87 on the fuel pump relay. I did that but I am getting constant power to the pump when the key is turned off. Any tips on how to wire the pump so that it only turns on when the key is turned on?

[GregAmy]

Circuit 30 is direct to the battery, so no surprise there. Instead, leverage the stock fuel pump relay.

Circuit 85 is keyed power and Circuit 86 is the solenoid ground to the computer. If you ground the Circuit 86 wire coming from the relay plate, wire III on the T4b plug, then the fuel pump will only be energized when the power supply relay is energized, thus only with the key on.

Do note that one of the safety features of the stock system is that it will not energize the fuel pump if the engine is not running. So, for example, your fuel pump turns off in a crash and you're upside down with the engine stopped but have not yet turned off the key.

You lose that protection when you have your fuel pump on with the key on.

[mb914]

Thanks for the help Greg. For some reason when I ground wire III on the t4b plug I’m not getting any power (12v) from the original fuel pump wire. I checked the fuse and also changed the relay. Can you think of any reason why I’m not getting power?

Circuit 30 is direct to the battery, so no surprise there. Instead, leverage the stock fuel pump relay.

Circuit 85 is keyed power and Circuit 86 is the solenoid ground to the computer. If you ground the Circuit 86 wire coming from the relay plate, wire III on the T4b plug, then the fuel pump will only be energized when the power supply relay is energized, thus only with the key on.

Do note that one of the safety features of the stock system is that it will not energize the fuel pump if the engine is not running. So, for example, your fuel pump turns off in a crash and you're upside down with the engine stopped but have not yet turned off the key.

You lose that protection when you have your fuel pump on with the key on.

[GregAmy]

For some reason when I ground wire III on the t4b plug I’m not getting any power (12v) from the original fuel pump wire.

I'm not clear I understand.

With the fuel pump removed, check for 12V at circuit 30 in the relay plate. I think that's going to be fine since you said the pump was running when you jumped 30 to 87.

With the relay installed and the key on, you should hear the pump running when you ground T4b pin III. It should go off when you turn the key off.

If there's any doubt that the power relay is working, you can remove it and jumper 30 to 87 and the pump should go on. Of course, since it's jumpered to the battery (circuit 30) then key position is not relevant.

[GregAmy]

Attached is the section of the wiring diagram; wire T14-13 goes to the fuel pump. By jumping 30 to 87 under the fuel pump relay you've demonstrated you can get battery power (30) to the fuel pump (87).

J17 is the fuel pump relay and J16 is the power relay. If the power relay is working correctly then when you turn on the ignition key it will power the T4b-I circuit. Then, connecting the T4B-III terminal to ground will energize the fuel pump relay solenoid, closing that same 30-87 circuit to the fuel pump.

If not:
- Verify jumping 30-87 on the fuel pump relay circuit turns on the fuel pump.
- If so, verify battery power on the T4b-I pin with the key on.
- If so, then with the fuel pump relay installed jumper 30-87 on the power relay and then ground T4b-III and the fuel pump should go on.
- If you are not getting battery voltage to T4b-I with the key on, then the power relay circuit is not working properly.

Ensure you're clear which terminals are which on the T4b plug. See attached, you are looking at this from the top...

EDIT: here's some notes on that terminal block from my Microsquirt design:

T4-I, Into ECU pin 16 (.75mm) and 24 (.5mm), Circuit 87, powered by engagement of the power relay.

T4-II, .5mm, Into ECU pin 18, Power from T14-1, signal to ECU of start circuit engagement

T4-III, .5mm, Into ECU pin 19, circuit 86, ground side for fuel pump relay.

T4-IV, .5mm, Cold Start Valve, from T14-1 (track 81) starting circuit voltage to CSV