EFI ECU Controlling the Cooling Fan Sanity Check

[RJD]

I have the Holley Sniper EFI and want the EFI's ECU to control when the cooling fan kicks on versus having the thermostatic switch do it.

As it is now, on the cooling fan relay, the fused power supply goes to pin 30 (power supply) on the relay. A jumper goes to pin 85 on the relay which is the ground. Pin 86 is the relay trigger and is connected via the green wire to the thermostatic switch for the engine block location, and another green wire which goes to the forward harness for mounting the thermostatic switch in the radiator (if configured that way). Pin 85 on the relay is the output and is connected to the blue fan wire via a fuse.

The Factory Five instructions say on page 38 of the Chassis Wiring Harness that in order to have the EFI control the fan, you should:

"Cut the short red looped wire that goes between the fan relay pins close to the left red wire connector it jumps from (pin 30 - power supply) and connect the EFI computer fan power wire to the red relay going to the bottom pin (pin 85 - ground)." The instructions also say to ground one of the thermostat switch green wires.

I think in the above configuration, the thermostatic switch would still trigger the relay and not accomplish the goal.

On the other hand, the instructions for the Sniper EFI say to wire it so the EFI triggers the fan relay, and notes that the EFI uses ground outputs to do so. The Sniper EFI also has its own coolant temperature sensor.

With the above in mind, rather than follow the Factory Five instructions, it seems that I should wire the EFI to pin 86 (the relay trigger) which should close the circuit in the relay when the EFI ECU sends it the signal, and let current flow from pin 30 (power supply) to pin 85 (output to the fan). Then I can eliminate the thermostatic switch in the engine block entirely, since the Sniper has its own coolant temperature sensor.

Am I on the right track?

[Papa]

Don't cut the jumper! All you need to do is run the Sniper's fan control wire to the fan's ground wire in either of the two locations provided on the RF harness. There is one at the top of the engine and one at the bottom under the radiator. The Sniper completes the ground to turn on the fan. The fan always has 12 volt power. The CTS (Coolant Temperature Sensor) supplied with the EFI will trigger the ECU at ~180 degrees (mine actually triggers when my gauge is reading ~190 degrees) to complete the circuit, which turns the fan on.

Use the light blue wire out of the Sniper's 10-pin connector for your fan control. Note that this is a (-) wire. I actually de-pinned the rest of that connector as I'm not using any of the other wires but the fan control.



Dave

[phileas_fogg]

Dave's got it exactly right; follow his instructions and you're good with respect to fan control.


John

[RJD]

Don't cut the jumper! All you need to do is run the Sniper's fan control wire to the fan's ground wire in either of the two locations provided on the RF harness. There is one at the top of the engine and one at the bottom under the radiator. The Sniper completes the ground to turn on the fan. The fan always has 12 volt power. The CTS (Coolant Temperature Sensor) supplied with the EFI will trigger the ECU at ~180 degrees (mine actually triggers when my gauge is reading ~190 degrees) to complete the circuit, which turns the fan on.

Use the light blue wire out of the Sniper's 10-pin connector for your fan control. Note that this is a (-) wire. I actually de-pinned the rest of that connector as I'm not using any of the other wires but the fan control.



Dave

Thanks Papa. Good! I'm not as far out of my depth as I thought.

I had already de-pinned the rest of the connector and was planning to use the light blue wire for the trigger. Just wanted to make sure I was approaching the relay correctly. I think we're on the same page. As it is now, the green (fan ground) wires go to the trigger (pin 86 on the relay), so connecting the EFI light blue wire to one of the green fan wires to trigger the relay makes sense.

Thanks for the sanity check. I appreciate your expertise, and am a big fan of your build blog.

Regards,

RJD

[RJD]

Dave's got it exactly right; follow his instructions and you're good with respect to fan control.


John

Yup - always listen to your Papa. Thanks John for confirmation.

Regards,
RJD

[Papa]

I really wish that FFR would remove the instructions about cutting the jumpers or at least make sure that they state that those instructions are for very specific EFI circumstances and may not apply to everyone. Understanding positive and negative control is something that could be added to the manual as well. If you understand that concept and can determine what your EFI is, then the rest is not too hard at all. Speaking of which, I still need to rewire my inertia switch after switching to the Sniper from the FAST EFI. The FAST used negative control to drive the fuel pump circuit, so I was using the RF relay to power my fuel pump. The sniper uses positive control and its own relay, so I'm no longer using the RF fuel pump relay at all. I'll likely rewire the inertia switch into the pump control wire on the Sniper.

Dave

[RJD]

The sniper uses positive control and its own relay, so I'm no longer using the RF fuel pump relay at all. I'll likely rewire the inertia switch into the pump control wire on the Sniper.
Dave

Yes, I did the same thing regarding the fuel pump. I might just do without the inertia switch. But in case I change my mind, I hope you'll post how you rewire yours.

[phileas_fogg]

Great minds think alike. I moved the RF inertia switch to be in-line with the Holley fuel pump power circuit. A couple of snips, a few crimps, & some heat shrink & you're done. I seem to recall that the switch is rated to 20A & the Holley system provides less than 10A, so no problems moving the switch.

While you're at it, use a multi-meter to make sure your inertia switch is wired correctly. A couple of years ago, RF was providing inertia switches wired to be normally open rather than normally closed. Swapping a couple of pins so that the wires were on the outside terminals (not the center) was the solution.


John

[RJD]

Great minds think alike. I moved the RF inertia switch to be in-line with the Holley fuel pump power circuit. A couple of snips, a few crimps, & some heat shrink & you're done. I seem to recall that the switch is rated to 20A & the Holley system provides less than 10A, so no problems moving the switch.

While you're at it, use a multi-meter to make sure your inertia switch is wired correctly. A couple of years ago, RF was providing inertia switches wired to be normally open rather than normally closed. Swapping a couple of pins so that the wires were on the outside terminals (not the center) was the solution.


John

So, I decided to incorporate the inertia switch afterall. Not that I doubted you, but I called Holley to see what they recommended and they essentially said to do what you did - install the inertia switch in series on the fuel pump power circuit downline from the Sniper relay.