What's up folks. I don't hope that it's ya had problems that will make it so you can help,,, but I'm wondering if anyone has specs, info, readings and stuff - on the outputs and inputs when it comes to the Coolant Fan Control Module and coolant temp sensor CTS on the XKs.

Context. Some of the good folks on the XJS form and I are trying to figure out what it would take to run an OE Jaguar PWM fan set up on the range of earlier Jaguar XJS cars... The earlier cars have a mechanical fan that really can struggle in stop and go traffic, hot weather and just in general. Many have gone electric but even that can be a bit challenging...for reasons

In the photo of the ED below it can be seen that besides the 2 B+ inputs, all that's left is the single white wire input. What info is that wire carrying, is the question...? It comes directly from the ECU... Where does it come from before that? The CTS?

Another question then is,,, could it possibly be a signal that directly matches the input being provided from the coolant temperature sensor (CTS) to the ECU? And if so, could a CTS from a Jaguar XKR (for instance) be place in one of those rad hose inline sensor holders, and be used to feed the signal to the coolant fan module? What voltage input would need to be fed into the CTS? 5v there and around?

Y'all see where I'm going with this... What do I need to know?
​​​​​​Thanks!

 

Hi Jay,
The fans on the 4.2 are variable speed, unlike the slow/fast of earlier cars. It's all done with square waveforms and PWM - like the fuel pump module. The ECM varies the duty cycle to adjust the fan speed, based on input from coolant temp sensor, etc. etc.

From the EG, the signal on that wire is :- "EM80-51 COOLING FAN MODULE CONTROL: PWM, 140Hz, POSITIVE DUTY CYCLE RANGE 7% – 95%"

I guess you could emulate that part of the ECM with a Raspberry Pi or a microcontroller, but I wonder if it might be easier to modify a 2-speed twin fan system from the 4.0. Am I correct that the XJS has only a single fan - viscous on early cars and electric on/off on the later MYs?

 

Hey Michael... Thanks!

As the day wore on I was thinking about how WRONG I was/might be about the nature of the signal coming into the coolant fan control module (CFCM)... Looks like I was wrong.

So, in your opinion it's not as simple as a voltage from the CTS that the CFCM translates (processor in the CFCM) into a usable signal, to run the fans?

It's been a long time since I was messing around with the fuel pump on the XKR and PWM ideas BUT I swear I had gotten to a point where I believed that it was the fuel pump control module itself that was taking a range of voltage between say .5mV and 5mV (or something like that) and translating that info into a hz valve to spin the pump... The important stuff happening in the module while the ECU was basically rerouting info it was taking from the fuel pressure sensor in the rail...? Super interested in what ya think about all this - "you're nutts" is a perfectly good response, lolBut you know that!
​​​​​​

 

Frayed knot. The ECM does that translation. The FCM is really just a power amplifier for the signal from the ECM:- again, like the FPM. Putting the control modules close to that which they control means not having to run multiple heavy-duty cables the length & breadth of the car.

No, the ECM does all the thinking. It's looking at the output from the FPS to decide how hard to drive the fuel pump.

You want simple? Get an MGB Four fuses and virtually no eletrickery to go on the fritz...

Indeed. As is anyone running an old Jaguar (myself excepted, naturally ).

 

"in the old days" they had two fans running in series ( slow ) or parallel ( fast) controlled by 3 relays. No electronics couple of bi metal temp switches in the radiator, I can draw you up a diagram if you want to go that way.
More recently they had two fans but had one running all the time and the second brought in by a temperature switch in the radiator or manual switch on the dash ...thats the easy way.
You could easily have two fans and run them in series (slow) all the time and switch to fast with a dash switch or rad temp switch.
On my 97 4l ( Not PWM) I have overridden the computer to bring them on slow all the time when the car runs and the electronics makes the full speed if required in the normal way. This has been great with a new 84 oC thermostat it sits at 88 deg unless you have the pedal to the metal.
If you need any wiring diagrams let me know and I will draw them up for you.
Addendum.
Found this switch on ebay .Its particularly good because it has change over contacts so that saves you a relay and its adjustable ( and its cheap). Just poke the sensor under the top hose clip and you are done.
Addendum 2
If your mechanical fan does not have a tight cowl then it will not be too effective.

 

Use two of those thermostats switches and a fan control module from the 97-02 XK8s with two fans and you could have off/low/fast.

 

Two thermostats with change over contacts will not give you series/parallel ( fast/slow)
One thermostat as previous picture + 1 relay will give you fast/ slow . Changes from slow to fast when the thermostat operates. No computers are required.
There is a screw in switch from a peugeot 405 still available with two sets of contacts which will switch two fans . Relays required.

 

Two thermostats like that can control the fan control module from an earlier XK8 - which was more or less the original question - giving off/slow/fast just like the XK8 but with no computers.

 

Good...... post a diagram

 

Here you go - lifted from the EG:



I've shown 45E via fuse to B+. If you don't want the fans to continue after switch off, then route through ignition.

 

Hey, Thanks to all... Apologies. I've been on the road and sea side the last couple of days so have been away from this.

I have a Derale Fan on the way, 2 speed, and intended to rig up 3 relays in the coming weeks. One for the low speed, one for the high speed and one for a manual control in the driver's seat. I guess the same or similar set up could be had for one of the dual OE Jaguar non-pwm fans. I think even direct wired PWM fans could work this way.

Still, with the number of PWM fans available, finding away to run one of these fan set ups as designed, PWM as the running temps vary would be a wonderful accomplishment... Especially if it could be done cheaply, reliably and with some robust-ness... One of the issues I think folks have always struggled with, with the addition of the electric fans, is the power drain on start up, all the wiring and and and...

I've started a thread today HERE on Bad Caps Forums (these dudes are amazing) and one of the guys there just linked this product as a start. Now I'm really scratching my head...

I'm also STILL very curious to take a reading from the CTS V output on my XKR and see if and how it compares to what's going INTO the fan from the ECU to control the fan. Just because.

 

It appears that item has a low frequency limit of 2kHz. I'm not sure how the 4.2 fan module will react as it's expecting a signal at 140Hz. I'd ask the vendor whether that lower limit can be reduced to around 140Hz as it is described as a default.

Perhaps this may be nearer the mark:
https://www.hicomponent.com/0-5v-0-1...er-module.html

...or, since they're cheap enough, just get one and try it.

Certainly food for thought.


From the EG, the signal from the ECM to the FCM is:- "EM80-51 COOLING FAN MODULE CONTROL: PWM, 140Hz, POSITIVE DUTY CYCLE RANGE 7% – 95%"

Output from the coolant temp. sensor to the ECM is:- "EM80-70 ENGINE COOLANT TEMPERATURE SENSOR SIGNAL, NOMINAL 0 – 5 V: NTC SENSOR – VOLTAGE DECREASES AS TEMPERATURE INCREASES"


I do like the idea of a manual switch, but I''d be the one to forget to turn them off and wonder why the car wouldn't start next time

 

Thanks for the diagram micheal ..I had expected some electronics but this is the standard relay system used back into the 1980s( peugeot 405etc) The peugeot switch (22mm thread) would work perfectly with W and WU and is still available.
The wiring can be simplified by the use of a 10Amp diode instead of the change over relay.

 

I'll let Jaguar know. 😁

 

Lol... Same here same here. A timer style relay?

I had a few days at the Sea,,, and intentionally left my phone somewhere.

I haven't gotten a lot of good replies from the bad caps forum folks after that first one (great group over there). I just offered up the NEW AND GOOD information you provided, Michael! Thank you. One thing, working on my phone for this stuff 95% of the time I miss a TON in diagrams and stuff, then two - the amount of things I DONT KNOW could fill an ocean. It's embarrassing sometimes, ya know?

Really, with the amount of information and the number of products and components available this doesn't seem impossible... Just using the info, resources and tools (like the NET) to pull it all together...

Me - this is such new stuff for me all I can do is pose the questions and wait for answers... I am hopeful though.

 

Still thinking about this...

I'm still just starting on my XJS electric fan adventure.
Really struggling with what I consider a massive voltage drop when the fans go from 000 to 100%%% instantly... Fans are in, wired and mounted but still looking for a better way.

Think I may have found a partial and I STILL want to access y'alls thinking and big brains. Here's the thing... The module from the Mazda 6 is readily available... -