Puma speedo question

[rocky]

I have a 90 tdci 07 plate and have heard that if you change tyres from 205/80/16 (which is on my vehicle)to 235/85/16, the difference in tyre size can be compensated for on the computer as the tdci's speedo is controlled by the computer. Would someone kindly confirm if this is correct--or not.

Regards, rocky.

[brighouse shed]

first thought is how will the computer know?

[Happyoldgit]

Split the above from another thread.

[western]

Thought I'd already posted a answer to this, the speedo gets it's signal from the ring in the transfer box via the transducer,

from the Tdci aka Puma Defender workshop CD

Speedometer

The instrument cluster receives a hardwired vehicle speed signal from the vehicle speed sensor. The vehicle speed

sensor is a Hall effect sensor located on the transfer box. The sensor acts on a reluctor ring located on the transfer

box rear output shaft. For additional information, refer to Transfer Case - Vehicles With: 6-Speed Manual

Transmission (MT82) (308-07 )

[pope-on-a-rope]

I have a 90 tdci 07 plate and have heard that if you change tyres from 205/80/16 (which is on my vehicle)to 235/85/16, the difference in tyre size can be compensated for on the computer as the tdci's speedo is controlled by the computer. Would someone kindly confirm if this is correct--or not.

Regards, rocky.

When mine was hooked up to the Autologic diagnostic machine (to see if there was an option to remove the speed limiter) it gave a number of tyre and speed combinations you could choose plus KMH and MPH options. Simple job to do IIRC.

[rocky]

Hi, thanks for the replies. rocky

[Crackle60]

Hi all,

Does the speed sensor on the transfer case send it's signal to the ECU concerned with speed limiting and then output by hard wire to the speedo instument? (Puma 2.2 )

Thanks and regards Peter

[Andrew Chua]

Signal from the mechanical output of the t-box to the transducer to the wires to the ecu.

The ECU works bases on the pulses it receives from the transducer. so the faster the output of the t-box the more pulses this fella outputs which in turn will feed the speedo.

see the thread on speedo run up circuit.

so back to your question, the sensor sends the pulses to the ecu and when the ECU sees a certain number of pulses, it will assume the truck is running at X km/h or X mp/h. I remember that someone posted the exact number of pulses for 1km/h, in the speedo run up circuit thread. so when the ecu has the required number of pulses it takes to cut in the speed limiter, it simply will moderate the output to the engine. so even if you floor the pedal after the speed limiter has kicked in, nothing happens.

the number of pulses from the transducer needs to fall below certain number of pulses (which translates to the km/h) before the speed limiter cuts out and then everything is back to normal.

the ecu has no idea of how large a tyre you are using. so if your ecu has been set for 7.50/16 and you now have 35" tyres fitted, technically, you will be able to travel at faster speed (having the speedo read slower) and hence the speed limiter cuts in "later". that also means 'less milage being covered. so being honest folks, you should calibrate your speedo when you change the tyre size.

The speed transducer doesn't care about the engine rpm either, so much so which gear you are in. the gear box also doesn't send to the ecu the gear number you are driving, so you can be doing 100mph (based on the pulse per minute) in gear 3 (if it's even possible). doing some assumptions, the ecu can figure out based on the rpm and speed (based again on the ppm).

Hence in the case of the Td5, if you fitted a 1.222 ratio box, the cruise control will not engage if you are in gear 5 as the ppm output doesn't match the acceptable range of the engine revs.

[AfricaKev]

Can anybody tell me what colour the speed sensor wire is on the 2010 defender puma please