ECU Electric Fan Control

by Michael Decipha Ponthieux
Last updated: 8-18-2013

Wiring

For foxbody ecu's It's necessary to insert a new pins into Pin41 of the ecu harness connector to use the high speed fan output.
I recommend cutting off a harness connector at your local scrap yard to take the pins out of.
Removal of the pins is as simple as releasing the 2 red retainers out of the connector,
and with a fine tip pick, hold the white locking tab over while you pull the pin out of the backside of the connector.

It isn't necessary to use pin55 for the low speed fan if you only have a single speed fan.
The low speed fan requires a little more work to properly function, most foxbody ecu's will not support the low speed fan.
The low speed fan output will only work on ecu's that have the additional fan hardware on the ecu board.
Most often, folks using the fan control wire up to the high speed fan output. This is acceptable but requires that a diode be used between
the a/c clutch and the fan relay to allow the fan to come on when the A/C is on. Obviously, this isn't a concern for those without A/C, of which I feel sorry for.

NOTE: For those whom are capable of using the low speed fan output, I only recommend using a TIP120 transistor.

Wire your fan as shown in the diagram below for EEC-IV ecu's. Verify your pin's by referencing the PINOUT LISTING
foxfan

Pin 41 on EEC-IV is a ground output for the high speed fan relay
Pin 55 on EEC-IV is a positive output for the low speed fan transistor

As you can see in the diagram, the ecu has to power off the low speed fan, any wiring issue from the
ecu output to the fan relay will result in the low speed fan being powered on, this is why the low speed fan
constantly runs when you have a corrupted tune, the ecu has to turn it off in the programming (same as fuel pump).

If using the high speed fan only, it is highly recommended to wire it up as shown below.
This will apply to most folks using an electric fan.
HIGH SPEED FAN WIRING

WARNING:

The ecu's output pin's are ONLY CAPABLE of supplying a maximum of approximately 200 milliamps, as with all microcontrollers
they are rated at much less for sustained use, the ecu fan output pins MUST BE CONNECTED TO A RELAY. DO NOT TRY TO POWER
YOUR COOLING FAN DIRECTLY WITH THE ECU PIN. This will damage the ecu.

Tune Changes

The following parameters will need to be updated for your fan to function correctly.
These memory locations given are for the GUFB strategy only.

PID	Parameter	Memory Location	Memory Size	Stock value (decimal)	New value (decimal)	Comments
EDFHP	LOW SPEED FAN ENABLE	0x941C	1 byte	0	1	ENABLES THE LOW SPEED FAN STRATEGY
HEDFHP	HIGH SPEED FAN ENABLE	0x941D	1 byte	0	1	ENABLES THE HIGH SPEED FAN STRATEGY
LSFECT	LOW SPEED ON TEMP	0x9414	1 byte	220	210**	ECT TO ENABLE THE LOW SPEED FAN
HSFEC2	HIGH SPEED ON TEMP	0x941F	1 byte	242	220**	ECT TO ENABLE THE HIGH SPEED FAN

Memory locations include a 0x2000 intel memory offset for the GUFB strategy only.

**I recommend setting the low speed fan to come on 16 degrees higher than your thermostat temp, and the high speed fan on temp to 10 degrees higher than that.
The above new values are based on a 195 degree thermostat.

Grade Load Strategy

The grade load strategy enables the high speed fan under heavy 'grade load'. Its implementation is flawed due to the fact that the fan would power on before the grade load
values are met. However, one can change the grade load parameters to allow the high speed fan to come on during heavy load. This is typically not needed.
The parameters are listed below.

PID	Parameter	Memory Location	Memory Size	Stock value (decimal)	New value (decimal)	Comments
HSFEC1	GRADE LOAD ON TEMP	0x941E	1 byte	234	210	MINIMUM ECT TO ENABLE GRADE LOAD
HSFLOD	GRADE LOAD MIN LOAD	0x9422	2 bytes	150	70	MINIMUM LOAD TO ENABLE GRADE LOAD
HSFRPM	GRADE LOAD MIN RPM	0x9420	1 byte	1808	3600	MINIMUM RPM TO ENABLE GRADE LOAD
HSFVS	GRADE LOAD MAX VS	0x9421	1 byte	40	128	MAXIMUM VEHICLE SPEED TO ALLOW GRADE LOAD

Memory locations include a 0x2000 intel memory offset for the GUFB strategy only.

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