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Summer is coming so I have been discussing with Merc07 for a chip mod to let the fans coming in sooner. I found that the cooling fans of my bikes do not kick in at 97c according to the spec but until the dash board shows around 108 - 110c. Also as advised by Adam fans on 750s might not be controlled by the ECU but by a thermal switch on left side of the engine, so that the chip might not work unless there is a wringing mod done to connect fan relay with the ECU.

According to previous threads about manual fan switch installation the wiring diagram to reference for 750s should follow the ORO where the fans for not controlled by ECU. Its worth a check whether there is continuity between the fan relay and ECU on my bike to make sure however I am already jammed in the first step, I don't know how to unplug the ECU....
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The picture shows my ECU, my understanding is that I have to first lift up the metal latch and then unplug, is it correct?

Any way to know the cause for the current out of spec fan kick in temp? Check both sensors of lower radiator and thermal switch?

Thanks!
 

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There are two temperature switches on an F4 750 EV 03. One is for dash indication, and that is on the radiator housing.

The other is to run the fans on and off and that is mounted on the engine block.

Those two switches probably do not correlate in temperature becasue of their locations.

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You are correct on unplugging the ECU...use a small flat blade screwdriver to lift the metal lock tab and then pull the connector up from that end, it will un-hinge from the other end and come off.

Based on the service manual page silentservice703 posted, the ECU is not controlling the fan on that model. Rather it is the thermo switch grounding that makes the connection.....but I would have to look at the wiring diagram to confirm this.
 

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Yep, that is true. Adam and I did discuss being able to enable that on the 750s. I looked petty seriously into it but found running a manual fan switch solved my problem. Read this page here:

 

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I'm another one who has talked to Adam about the hot F4's and likes the manual fan, because you can kick it on before you even get into the slow area which helps a lot, I know because I try it.. My plasma ceramic coated down pipe where it wants to burn and split the belly pan gets 100C hotter for every 15C of increased engine temp. Before I had the manual fan switch on my 750 display temp could get over 105C which is 230C+ more to melt the bodywork over standard operating temp. I suspect non Plasma ceramic coated pipes are going to show even bigger increase's in surface temp.
 

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I had Adam make a chip for me. My 2000 750S has a computer controlled fan. I can't understand why a 2003 EVO would not be computer controlled.
 

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Ok, so I ws curious now that there are two folks saying they have the same bike with differing control system...not likely.

Here is the enhanced wiring diagram showing there is an ECU input to cooling fan control. I did not enhance the entire diagram, but enough to show that the engine block temperature sensor inputs the ECU and the radiator temperature sensor inputs the dash.

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And there you have it !!! Thanks for looking at the schematic and answering the question Chuck..... Makes sense the ECU would be the activating signal as the fuel maps will also have transients for changes in engine temps.
 
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Hi Chuck and esq'z me, just out of interest did either of you read posts 21-30 in the above thread link from Glenno? Thermostatic fan switch installation Donsy and Merc07 made some interesting comments, it seems everything is not fully connected, it could possibly be someone had actually connected things up on one of the bikes? 2 quotes from Adam below:

"As you quoted earlier, the ECU pin for the fan output is the same as on the 1000 and does exactly the same thing but it is just not connected to the fan circuit.
I'm sure it would only need a simple modification then you could set it to what ever temp you want."

"Had a quick look in the manuals.
Check pin 20 on the ecu, see if it goes low at around 98C, the software code is in the eprom and is working so you should see a change of state.

If you see the change then it should be quite simple.

You would have to remove the fan thermal switch and join the 2 wires (No.32)
Disconnect the wire from pin 85 of the fan relay (No.48)
Connect a wire from pin 20 of the ECU to pin 85 of the fan relay (No.48)

The only difference I can see is that the fan relay on the 750 has a diode built in where as the one on the 1000 that connects to the ECU dosen't - not sure if that matters ?

Check the wiring diagrams so you are happy with the above - don't blame me if it smokes though....! "
 

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That is a n interesting read. Adam does a lot of research on these things and I'd tend to defer to him...but, the wiring diagram I posted is for the 750S. It appears to show the ECu pin is connected to the Engine Block Temperature Sensor as is the Fan Relay. Now, the ECU uses Engine Temperature for many functions.

Something seems amiss to me though: As the Fan Relay (47) powers the fans directly, and the Fan Relay (47) is powered from the General Feed Relay (20), and the General Feed Relay (20) is always powered when the Ignition Switch (34) is turned to the RUN position, then it would follow that the fans are always on...but they are not.

There must be a control mechanism, but I do not see it on the 750S wiring diagram.

@merc07: Adam, what am I missing?
 

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Discussion Starter #12
Thanks everyone! Hi Chuck, for “General Feed Relay (20) is always powered when the Ignition Switch (34) is turned to the RUN position, then it would follow that the fans are always on...but they are not.”

I thought the engine block sensor is some kind of analogue switch that turns on when it senses 97 c and power the fans?
 

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The 750 ORO diagram includes no.32, Fan Thermal Switch that controls the fans..
The F4S diagram has the Thermal Switch emitted and I assume should have pin 85 ( -v coil) of the fan relay connected to pin 20 of the ECU, not straight to ground as silent pointed out.
This would be the same as the 1000S circuit.
 

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I have a 2000 750s and no ECU control on the fan. The wiring doesn't support it. Are you sure it isn't the thermo stat switch turning them on?
100% positive., as the chip from Merc07 changed the cooling fan schedule.

My bike also appears to have been converted to the dual radiators. I am unsure if this was pre or post purchase. My assumption is that the circuit was enabled at that time.
 

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@Drewbert34, the two rad system was installed on early the early F4 from frame number 001153I on...

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