My son's recently put his Mk1 Focus RS back on the road after a 3 year long rebuild.

The Ford ECU is still in place, mainly just to run the dashboard cluster, but all of the engine management is now controlled by an Omex 710

It's running a base map at the moment just so we can get some miles on it before it goes off for final mapping, but we have a small problem with the rad fans.

Both fans start running as soon as the engine starts and don't go off. The water temp warning light is on on the dashboard, I presume because the temp sensor is no longer connected to the Ford ecu (so we need to to sort that), but what's telling the fans to come on? The fans are set in the Omex to come on at 95 and off at 85, so something somewhere else must be telling them to come on.

Could the Ford ECU still be telling the fans to run if it thinks the engine's overheating? Is there another wiring route to the fan motors somewhere?

There's some electronic thing at the top right of the radiator that seems to feed into the rad fan wiring. What's that?

Oh, and the aircon has been removed in case that may have some bearing? we've tried all the usual tricks of setting the aircon switches to certain places etc to no avail

Any thoughts anyone?

 

It does sound to me that the engine ecu is thinking the engine is too hot.

 

Think your going to need a Bespoke fan loom from the omex to the fans.
sure you have not spliced into circuit for the fans?

Engine hot fans come on
AC on fans come on

switch ignition on and start pulling fuses and see which circuit shuts them off.

 

Pull the fan relay and they stop.

Was thinking about putting a switch in, but might have to start pulling things apart again and having a look at how things are wired up

 

If the Ford ecu isn't seeing correct values it may be putting the fans on as it think a there is a problem.

A lot of cars if you unplug the coolant temp sensor the fans will come on.

 

That's exactly my thinking, just a bit stumped as to how it's still controlling the fans though as the fans are now controlled by the Omex

 

The CHT sensor missing will activate the fans as a major fault has been logged.

They must still be controlled via the original ECU.

Martin

 

Or there a fan switch on the radiator? If so you could use a aftermarket cossie fan wiring loom and relays.

 

No there's no switch like the Cossies I'm afraid. That would have made things simpler.

 

Sorted.

The Ford ECU was controlling the high speed fan relay, and overriding the Omex.

Removed the high speed relay, which allowed the Omex to control the fans. Now comes on/goes off at the required temps!!

 

Bonus matey. Glad you got it sorted.

 

Yeah nice one. Glad you got to the bottom of it, and also it's nice to see a problem thread finished with the solution.

 

 

He's already sorted it!

 

 

I suspect this may be what catches many out with the MK1, that being that when windscreen direction is selected the A/C is on, as it's a great dehumidifier.

Martin