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When does the fuel pump run


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Hi,

 

I have "cleaned up" the OEM wiring and now the fuel pump doesn't work. Everything from the relay to the pump works but for some reason the ECU doesn't turn it on. It's supposed to pull a wire low.

My standalone that I used to run would prime the fuel pump on power on and then only run when RPM was > 800 or so.

Would a OEM ECU (NC Miata) work the same?

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The NB oem ECU does not prime, only runs once cranking.  Not an NC but it’s a data point. 
 

Standalone ecu’s will do pretty much whatever you want.  I set mine to prime 3-5 seconds with the key on. 
 

 

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7 hours ago, ETR said:

The NB oem ECU does not prime, only runs once cranking.  Not an NC but it’s a data point. 
 

Standalone ecu’s will do pretty much whatever you want.  I set mine to prime 3-5 seconds with the key on. 
 

 

 

Thanks, I guess the NC work similar.

I probably connected the fuel pump to the interior dome light or something....

 

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Not the same, but on the old school GSL-SE rotary the fuel pump would only run if it had a signal from the air flow meter. This is how they insured that the engine was running and shut the pump off if the engine died. Not likely to be the same problem, but the OEM system can have all kinds of controls that you wouldn’t think about dealing with safety and emissions.

 

Does it have an inertia switch somewhere which could have been triggered? They use those to shut the fuel pump off in a crash, at one point we were looking to sell those to the racing market, so we installed one in a race car, but didn’t hook it up, only logged if it was triggered. Every pass the switch was triggered, guess a 6 second 200mph car created enough G force for the switch to think it had crashed.

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On my cars, I have a separate switch for the fuel pump so that I can avoid any ECU/ relay module glitches. Master switch shuts everything off anyway. 

 

It's nice for testing fuel pressure, comparing injector volume and spray pattern, draining the tank, etc.

Edited by mender
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1 hour ago, mender said:

On my cars, I have a separate switch for the fuel pump so that I can avoid any ECU/ relay module glitches. Master switch shuts everything off anyway. 

 

It's nice for testing fuel pressure, comparing injector volume and spray pattern, draining the tank, etc.

The only way I would Wire through a switch would be an addition to the factory, it’s nice knowing when the engine quits it takes care of itself.

 

I was in a fiery crash bad enough it hurt trying to turn the car off, but was aware it was no longer running, I had a concussion and limited amount of time to get out, I used all remaining energy to do just that…. Unbeknownst to me, the fuel lines, main harness, and exhaust were all severed, if the pump continued to run with my injury, and limited thought process, it would’ve been much worse.

Edited by Team Infiniti
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1 hour ago, mender said:

On my cars, I have a separate switch for the fuel pump so that I can avoid any ECU/ relay module glitches. Master switch shuts everything off anyway. 

 

It's nice for testing fuel pressure, comparing injector volume and spray pattern, draining the tank, etc.

 

57 minutes ago, Team Infiniti said:

The only way I would Wire through a switch would be an addition to the factory, it’s nice knowing that the engine quits it takes care of itself.

 

I was in a fiery crash bad enough that it hurt trying to turn the car off, but was aware it was not running, I had a concussion and a limited amount of time to get out, I used all of my energy to do just that…. The fuel lines, main harness, and exhaust we’re all severed, if the pump continued to run with my injury and limited thought process it would’ve been much worse.

I run the fuel pump hot wire through the main switch panel so that I can selectively toggle it on / off. A relay (triggered by the ECU) is worked into the circuit with insulated spade connectors and it can be excluded from the circuit in about 10 seconds. In the garage I omit the relay and can run the pump with the switch. For races the relay is reintroduced to the circuit for the safety reasons pointed out by @Team Infiniti.

 

(this is probably the third time I've written exactly this on the forum, but I think it's the way everyone should wire their fuel pumps, so it's worth repeating for anyone new or for those who haven't adopted yet)

Edited by enginerd
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20 minutes ago, enginerd said:

 

I run the fuel pump hot wire through the main switch panel so that I can selectively toggle it on / off. A relay (triggered by the ECU) is worked into the circuit with insulated spade connectors and it can be excluded from the circuit in about 10 seconds. In the garage I omit the relay and can run the pump with the switch. For races the relay is reintroduced to the circuit for the safety reasons pointed out by @Team Infiniti.

 

(this is probably the third time I've written exactly this on the forum, but I think it's the way everyone should wire their fuel pumps, so it's worth repeating for anyone new or for those who haven't adopted yet)

What's the purpose of the switch? When would you use that?

 

I have mine wired the same, except no switch. If I want to drain my cell, or disable the fuel pump, I have the spade connectors on the relay and takes 2 seconds in the trunk.

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30 minutes ago, petawawarace said:

What's the purpose of the switch? When would you use that?

 

I have mine wired the same, except no switch. If I want to drain my cell, or disable the fuel pump, I have the spade connectors on the relay and takes 2 seconds in the trunk.

If I want to kill power without turning off the ECU. There may be some code checking / data logging / ECU type things in that realm where you want to keep the ECU powered during and after engine shut off. Also I've read that you shouldn't kill the engine with the kill switch or it can cause alternator issues (but we have done this hundreds of times and never failed an alternator) so this allows you to kill with fuel and then turn off the main power after that.

 

Also, let's say the car stalls on track and I suspect a fuel leak. I want to pull off the track but I don't want the fuel pump to run. I turn off the fuel pump switch, leave the others on, put car in 1st gear and limp it forward on the starter motor.

Edited by enginerd
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The NA/NB Miata's have a port on the "data link" that allows you to trigger the pump on (with the ignition).  They have the relay hot all the time, then switch the ground so if you ground the trigger by another means it will run the pump.  Don't know if that is the same set up as the NC's. 

 

I had a Nissan that didn't have this sort of thing so I wired up a set of leads with a plug that matched the OE plug to the fuel pump that I could just plug in when I wanted to drain the tank.  It did lead to a funny interaction at the track where I got out the wire, set up jugs, pumped all the fuel out of the car, then just dumped it back in.  The guy camping next to me was confused until I told him the fuel gauge wasn't very accurate so the only way I could tell how much fuel was in it was by emptying and refilling.  His response was simply "and what type of engineer are you?"  I told him mech-E and he nodded.

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Turns out the NC Miata has 3 RED/WHITE wires from ECU connector 1:

- Fuel pump control

- Fan relay

- EVAP stuff

 

I had the relay connected to EVAP......

 

Fixed it and runs like a champ!

 

edit:

It primes for a second when ignition is turned on and then when it's running. I don't believe it tries to run while cranking.

 

Edited by turbogrill
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