CSR Speedometer Failure

[David.Ashley.Poole]

Hello L7Cs,

after my car was remapped by the two Steve’s the speedometer stopped working - due, I think, to the vibration on the rolling road (they took it to 160 mph (!)).  I pulled all the instruments out to see if anything was disconnected or damaged, but everything looks fine.  I also replaced the sensor and set up the clearance.. but is still does not work.  I cannot find the 1 kOhm pull-up resistor on the sensor line, and it does not appear to be connected from the VOM readings.  Could anyone help me with what the thing looks like (is it just a standard 0.25 W resistor) and where it might be hiding?  Or any other suggestions?  The tach pull-up is quite obvious but it is a 4W and has its own connector.   Hoping you can help - you are my only hope, Obi-Wan....

[Jonathan Kay]

Driven from a rear wheel?

Fuse OK?

Have you got the Workshop Notice on modifying the wiring?

I also replaced the sensor and set up the clearance.. but is still does not work.

Was that using the telltale light or the gap alone?

Jonathan

[David.Ashley.Poole]

Hello Jonathon,

You are a good chap, I must say. - always ready to help.

But the problem is resolved, but not (yet) fixed.  I was mulling the issue over and remembered that the wheel speed sensor line also goes to the ECU.  So I wondered if perhaps the new ECU - MBE9A4 - was not terminating the line correctly.  And so it proved - I swapped back to the original ECU and, voila, the speedometer is working again. So I will talk to SBD on Monday and poke around with EasyMap and see if I can reconfigure the line.  The 160 mph rolling road fracas and the pull-up resistor are red herrings, and I will look into the latter more deeply.

I would be very grateful if you could send me the details on the telltale light method of setting the wheel speed sensor (I used a go/nogo gauge that I made), and also the bulletin on setting roller barrel throttles to see if there is anything I have missed.  And I must apologize for not sending you the CSR documentation that I promised - I was distracted by work but will try and do better in the future...

[aerobod - near CYYC]

On my 2012 R400D when I fitted the 9A4 ECU, SBD required a 1K pullup resistor on the wire from the ECU to the speedo, to pull the voltage up to 5V (ECU Pin 27 on my car). Also in the 9A4 Easimap "Programmable Pins", I have "Speed Input Source" set to Pin 27.

Tacho pulses per cycle was set to "1" in the default map I received from SBD, I had to set that to 4. I also had to change the TPS behaviour to match the default Caterham plenum TPS.

[David.Ashley.Poole]

Hello Aerobod,

 

thanks - just talked to Craig at SBD, and he told me the same thing - pin 27 pull-up resistor needed.  No wonder I could not find it behind the dash.... presumably the 992 has an internal pill up resistor?  But he also said that the 9A4 does not use the Wheel Speed Sensor input... I will check and see what the tach is set to - presumably the 9A4 uses the tach input?  The CSR has roller throttle bodies and the standard Ford TPS so presumably that is OK.  Anyway, that car drives very well, if at some unknown speed.  LOL.

Thanks for the help - and if you have other comments I would be very interested.

[David.Ashley.Poole]

Thanks to Craig and the gang at SBD everything is now clear.  Well, almost.  This is what I received from them:

”The ECU itself is not used for any function for the speedo, for some reason Caterham had made a mistake on their wiring and not fitted a pull up resistor to strengthen the signal from the wheel speed sensor to the speedo, so they found a pin on the ECU that had a pull up resistor fitted and used this to pull the signal strength up. As you can see from the notes below, they have connected it to Pin 27, the original ECU design had a 1K pull up, unfortunately this limits the ECU’s use if the pin is to be used for other functions. By fitting a 1K pull up resistor between Pin 27 and a 5v reference on the ECU, your speedo will then function, this can be done at the most suitable place either in the hood of the ECU wiring harness connector or further away if a suitable location is found. If you use a 0.25w resistor, this is easier to handle, anything smaller could be used but is very fiddly to work with”

So I have decided to use a two-pin plug and socket under the dash for this function, similar to the one being used for the 68 Ohm resistor for the tach.  The reason is that I can still revert to the original ECU by unplugging the resistor...I could get the same effect by cutting the wire to pin 27 and pulling it high on the 12v power pin, but I am mildly uncomfortable with that idea.  The only slightly obscure thing left is that SBD recommends pulling it up to the 5 volt TTL reference, while,Caterham and Caerbont clearly use the 12 volt line.  So a call to Caerbont tomorrow should resolve this...

[Jonathan Kay]

I would be very grateful if you could send me the details on the telltale light method of setting the wheel speed sensor (I used a go/nogo gauge that I made)... 

phatcat's suggested procedure. (I suspect you're using the same readings.)

Jonathan

[David.Ashley.Poole]

Thanks, Jonathon.  Very interesting, and I shall use it if I have any problems.  I have just been buying two pin connectors to splice the resistor into the wiring harness behind the speedo...