Idle hunting with electric fan.

[rosco15]

Holley Sniper on a 396 BBC in '62 Chevy Biscayne. Idle is fairly stable. When the electric fan comes on idle begins to hunt. Voltage drops from 14.2 to 13.6. IAC goes from five at idle up to 10 with the fan on. This is a new install. Fan is controlled through separate temperature switch and relay. Just wondering where I should look first?

[Danny Cabral]

This is usually due to voltage drop when large, high amperage dual electric fans turn on. Ensure the electrical system (alternator, charge cable, battery, etc.) is adequate, engine block is well grounded (LINK), and the electric fan wire gauge (AWG) is sufficient. Also, look at where the live cursor moves to during this occurrence, and ensure that area of the Base Fuel & Timing Tables are well tuned. However, if all engine hardware & EFI tuning is optimized and the fan condition persists, then read post #4 below. I successfully created an Advanced 1D Table to prevent the idle RPM dip when large, high amp dual electric fans turn on. This Advanced 1D Table works extremely well, and completely eliminates the momentary idle RPM dip!
https://forums.holley.com/showthread...869#post211869 (Advanced 1D Table For Electric Fan Idle RPM Dip)
For Sniper EFI only: https://forums.holley.com/showthread...115#post242115 (Fast Idle Function For Electric Fans - Sniper EFI)

[rosco15]

Right now negative from battery only goes to engine block. Not to chassis. I'll look at the wiring also. I just redid the fan wiring, but don't recall what size I used. I'll start there. Thanks.

[Danny Cabral]

This is usually due to voltage drop when large, high amperage dual electric fans turn on. Ensure the electrical system (alternator, charge cable, battery, etc.) is adequate, engine block is well grounded (LINK), and the electric fan wire gauge (AWG) is sufficient. Also, look at where the live cursor moves to during this occurrence, and ensure that area of the Base Fuel & Timing Tables are well tuned. However, if all engine hardware & EFI tuning is optimized and the fan condition persists, then read below. I successfully created an Advanced 1D Table to prevent the idle RPM dip when large, high amp dual electric fans turn on. This Advanced 1D Table works extremely well, and completely eliminates the momentary idle RPM dip!

Advanced ICF - 1D Table
Name: "Fan Kick". (I named it "Fan Kick" because it performs the same momentary IAC Position increase as the A/C IAC Kick.)
Table Type: IAC Position Offset
X Axis: Time
Switched Enable: Electric Fan #1, Enabled
IAC Position Offset table - top row: IAC Position % Increase
12, 9, 6, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0%
IAC Position Offset table - bottom row: Time (sec)
0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5
Advanced Enable: You can also activate it when TPS is Below 2%, so it's inactive at higher RPM or while driving.
https://hosting.photobucket.com/imag...D_Fan_Kick.png (Advanced 1D Table For Electric Fan Idle RPM Dip)
https://forums.holley.com/showthread...115#post242115 (Fast Idle Function For Electric Fans - Sniper EFI)

If the Advanced menu icon (ICF) isn't already uploaded (added) to the top Toolbar, follow these instructions:
(This same procedure applies to all the various Individual Configuration menu items.)
The Advanced ICF function is an "Individual Configuration" of the Holley EFI software.
At top of screen, Click "Toolbox" and "Add Individual Config".
At top of new window, select "Individual Configuration Library".
At bottom of new window, select "Holley EFI Advanced Config".
Select "Advanced" and open "default.adv".
The "Advanced ICF" icon will then be present at top of screen.

[rosco15]

I have that EFI software downloaded. I just ordered the cable so I can hook my laptop up to the Sniper and start learning the program. That picture helped a ton. Thanks!

[Danny Cabral]

You're welcome. Some people use PWM electric fan control, but I'm just not interested in that.
I run a 180° thermostat, and I run both Spal 12" dual electric fans on at 185°F & off at 182°F.
Works perfectly and the fans aren't on for very long. Curved fan blades really are much quieter.
I also want maximum cooling & airflow through the A/C condenser whenever the A/C is on.
https://forums.holley.com/showthread...Fan-Holley-EFI (Wiring An Electric Cooling Fan - Holley EFI)
http://forums.holley.com/showthread....0372#post60372 (PWM Electric Cooling Fan Instructions)
http://forums.holley.com/showthread....0371#post60371 (PWM Electric Cooling Fan Instructions)