Why the ECU should control the pump
A pump wired straight to the ignition switch keeps running as long as the key is on, even if the engine has stalled and a fuel line has been torn open. With ECU control, the pump only runs while the ECU sees the engine turning, plus a short prime when you first switch on. That is the main reason every Haltech install we do has the pump on an ECU output.
The Fuel Pump function in ESP handles the primary pump and up to three auxiliary pumps.
Wiring: always through a relay
An ECU output is a signal, not a power supply. A fuel pump draws far more current than any ECU pin is built for, so the pump is always powered through a relay, with the ECU only switching the relay coil. Never wire a pump directly to the Elite.
Elite digital pulsed outputs (DPOs) only ever switch to ground. The usual layout is:
- One relay coil terminal to switched +12 V.
- The other relay coil terminal to the DPO you choose in ESP. By default the primary pump uses DPO-5.
- The relay's switched contacts carry battery power, through a fuse, to the pump.
A 30 A 5-pin power relay suits most single pumps, and the waterproof mini fuse and relay box keeps it tidy. If relays are new to you, read how relays work and why you need one, and see the fuel pump wiring guide for the diagram.
Changing an output's Active State only decides whether it is normally on or normally off. It never turns a ground-switching DPO into a 12 V supply. If your relay needs a 12 V trigger, rewire the coil, don't hunt for a setting.
Pump modes
On the Wiring tab, set the mode for the primary pump, and tick any auxiliary pump (1 to 3) you want to use, then set its mode too:
- Digital - Switched: plain on/off. This is what almost every relay-driven pump uses.
- Digital - Duty Cycle: the output is pulsed so a variable-speed pump controller can run the pump slower when demand is low. It unlocks the PWM Signal Frequency setting.
Fuel Pump tab
| Setting | What it does | Our advice |
|---|---|---|
| Prime Time | How long, in milliseconds, the pump runs at key-on if the engine isn't turning | Long enough to bring rail pressure up before cranking. Check with a gauge, not by ear |
| PWM Signal Frequency | Pulse frequency when the pump is in duty cycle mode | Match whatever your pump controller expects |
Staging auxiliary pumps
A big power street car needs a lot of fuel at full load and very little at cruise. Running two pumps flat out all the time, or one enormous pump, makes noise and heats the fuel as it circulates back to the tank. Staging solves that: the second pump only switches on when the engine is working hard enough to need it.
Plumbing matters as much as settings here. The auxiliary pump goes in parallel with the primary, and a check valve is needed so fuel can't be pushed backwards the wrong way through the system. Power it through its own relay. Either the positive or the ground side of the pump can be the one the relay switches.
Aux Fuel Pump tab
| Setting | What it does |
|---|---|
| Trigger Type: Load & RPM | The pump turns on once engine load and RPM both pass their thresholds |
| Trigger Type: Estimated Fuel Flow | The pump turns on once the ECU's calculated fuel flow passes a threshold |
| Estimated Fuel Flow | The flow threshold, used only with the fuel flow trigger type |
| RPM Threshold / Load Threshold | The switch-on points for the Load & RPM trigger type |
| Time Hysteresis | The shortest allowed gap between one on/off change and the next, so the pump can't chatter |
| PWM Signal Frequency | Pulse frequency, only when this pump is in duty cycle mode |
We prefer the estimated fuel flow trigger when the fuel model is set up properly, because flow is exactly what the second pump is there to supply. Whichever you use, bring the pump in early: well before the primary pump runs out, not at the point it already has. Then log fuel pressure through the switch-over to confirm it holds steady.
Troubleshooting
| Symptom | Usually |
|---|---|
| Pump never primes | Relay coil not getting switched 12 V, wrong output selected, or Active State inverted |
| Pump runs all the time, even key-on engine-off | Active State set the wrong way, or the relay is wired to bypass the ECU |
| Fuel pressure drops when the second pump starts or stops | Missing check valve, or aux threshold set too late |
| Aux pump clicks on and off | Threshold right at a common cruise point, or time hysteresis too short |
FAQ
Can the Elite run a variable-speed pump?
Yes. Set the pump to Digital - Duty Cycle and set the PWM Signal Frequency to suit the pump or its controller. If you're not sure what your pump needs, ask us before you wire it.
Do I need a separate relay for each pump?
Yes. Each pump gets its own relay and fuse, switched by its own ECU output. For help planning a multi-pump system, get in touch.
