Mo Murphy
Active Member
Morning discool, that's the very question that I'm asking
The early ones used the cable to run the speedo and provided speed data to the 14CUX ecu. The TD5 defender version supplies info to drive the speedo electronically and provides the TD5 ecu with data (worthy of note is that here is that YBE100540 for the discovery, whilst externally identical to 530 sends a different number of pulses up its signal wire).
So what's the difference ? I don't know, hence my question will YBE100530 send a recognisable signal to the 14 CUX ecu that the ecu can interpret accurately ?
Mo
The early ones used the cable to run the speedo and provided speed data to the 14CUX ecu. The TD5 defender version supplies info to drive the speedo electronically and provides the TD5 ecu with data (worthy of note is that here is that YBE100540 for the discovery, whilst externally identical to 530 sends a different number of pulses up its signal wire).
So what's the difference ? I don't know, hence my question will YBE100530 send a recognisable signal to the 14 CUX ecu that the ecu can interpret accurately ?
Mo
discool
Well-Known Member
The 14CUX ECU does require a road speed input to give the ecu an indication that the vehicle is slowing down perhaps to stop , something below 7mph I believe, and therefore the ecu will control the idle control valve, if it doesn't the engine will stall.
This link shows that pin 6 of the ecu is the road speed input. Also stated, the ecu expects to see a variable voltage 0-12 six times every revolution of the transducer.
https://en.m.wikipedia.org/wiki/Lucas_14CUX
Last edited:
cooltide
sheep fancier
No it doesn't, it will return to idle. Running high consumption ancilliaries like a/c whilst stopping in an auto may cause a stall though
discool
Well-Known Member
Road Speed Sensor and everything I need to know for now. 
A cut & past from the ACT web site.
If the Road Speed Sensor is defective then the vehicle will tend to stall when you pull up to a halt with it. Secondly a fault code will be set in the ECU, which effectively disrupts operation of the Oxygen feedback system on catalyst equipped cars. Under certain circumstances this can dramatically shorten the life of the cats.
The reason for stalling with a defective (or absent) Road Speed Sensor is quite simple. Under normal operation when slowing down for a halt, the throttle may be closed but the engine is being driven by the inertia of the vehicle whilst the car is in gear (overrun). Because of the Road Speed Sensor the ECU will not try to adjust the idle in these circumstances, so the idle control valve is held open until the vehicle halts. The effect of this is that when the vehicle does halt, the idle valve is open and the ECU drops the engine onto idle smoothly.
However if the road speed signal is not present then the ECU attempts to adjust the idle whilst the engine is being overrun. Obviously this is a task it cannot accomplish – a fact that is recognised by setting a fault flag. In this case the idle valve is closed when the vehicle comes to a halt because the ECU has been trying to shut down the idle speed. Therefore it is a question of whether the ECU can lift the idle before the engine stalls.
Diagnosis of these simple devices is very straightforward. The road speed signal appears on the yellow wire (usually yellow/pink on later “Serpentine” vehicles) at the main connector where the fuel injection loom plugs into the vehicle body loom. Obviously the location of this plug varies between models of vehicle. In general for Land Rover vehicles it is at the top of the right-hand foot well (viewed from the driver’s seat) next to the transmission tunnel.
This signal is tested by monitoring the Yellow wire with the positive probe of the Voltmeter, with the negative probe connected to a good chassis ground. Switch on the ignition, and roll (or drive) the vehicle slowly in whichever direction is most convenient. The signal should go up and down between 0-2.0 Volts and 10.5-13.0 Volts, changing every 4-5 metres. This signal is 8000 pulses per mile.
Road speed sensors are serviceable to a certain extent. They are very simple devices internally, consisting of a toothed magnetic rotor that runs past a reed switch. The reed switch is mounted on a simple circuit board in series with a 120 Ohm resistor. Often the device gets water in it, which destroys the circuit board. Inspection of the device reveals that four bifurcated rivets hold on the end plate. If you drill out the rivets then it will just come apart (no spring-loaded stuff inside!). Reassembly is easy using a small self-tapping screw into each rivet hole.
Note that all Lucas 14CUX (and GEMS systems) have a road speed limiter programmed in their software. According to the model this may be at 105 or 112 MPH. At first sight it appears that you could disconnect the road speed sensor itself to remove the limit, but the only correct way to get around this is to reprogram the ECU. Simply disconnecting it will cause the nasty stalling problems listed above.
A cut & past from the ACT web site.
If the Road Speed Sensor is defective then the vehicle will tend to stall when you pull up to a halt with it. Secondly a fault code will be set in the ECU, which effectively disrupts operation of the Oxygen feedback system on catalyst equipped cars. Under certain circumstances this can dramatically shorten the life of the cats.
The reason for stalling with a defective (or absent) Road Speed Sensor is quite simple. Under normal operation when slowing down for a halt, the throttle may be closed but the engine is being driven by the inertia of the vehicle whilst the car is in gear (overrun). Because of the Road Speed Sensor the ECU will not try to adjust the idle in these circumstances, so the idle control valve is held open until the vehicle halts. The effect of this is that when the vehicle does halt, the idle valve is open and the ECU drops the engine onto idle smoothly.
However if the road speed signal is not present then the ECU attempts to adjust the idle whilst the engine is being overrun. Obviously this is a task it cannot accomplish – a fact that is recognised by setting a fault flag. In this case the idle valve is closed when the vehicle comes to a halt because the ECU has been trying to shut down the idle speed. Therefore it is a question of whether the ECU can lift the idle before the engine stalls.
Diagnosis of these simple devices is very straightforward. The road speed signal appears on the yellow wire (usually yellow/pink on later “Serpentine” vehicles) at the main connector where the fuel injection loom plugs into the vehicle body loom. Obviously the location of this plug varies between models of vehicle. In general for Land Rover vehicles it is at the top of the right-hand foot well (viewed from the driver’s seat) next to the transmission tunnel.
This signal is tested by monitoring the Yellow wire with the positive probe of the Voltmeter, with the negative probe connected to a good chassis ground. Switch on the ignition, and roll (or drive) the vehicle slowly in whichever direction is most convenient. The signal should go up and down between 0-2.0 Volts and 10.5-13.0 Volts, changing every 4-5 metres. This signal is 8000 pulses per mile.
Road speed sensors are serviceable to a certain extent. They are very simple devices internally, consisting of a toothed magnetic rotor that runs past a reed switch. The reed switch is mounted on a simple circuit board in series with a 120 Ohm resistor. Often the device gets water in it, which destroys the circuit board. Inspection of the device reveals that four bifurcated rivets hold on the end plate. If you drill out the rivets then it will just come apart (no spring-loaded stuff inside!). Reassembly is easy using a small self-tapping screw into each rivet hole.
Note that all Lucas 14CUX (and GEMS systems) have a road speed limiter programmed in their software. According to the model this may be at 105 or 112 MPH. At first sight it appears that you could disconnect the road speed sensor itself to remove the limit, but the only correct way to get around this is to reprogram the ECU. Simply disconnecting it will cause the nasty stalling problems listed above.
Last edited:
jamesmartin
Well-Known Member
ive fitted 3.9s without speed sensor seemed to run normalHere we go again. Wikipedia + whatever blurb was above vs experience
Mo Murphy
Active Member
Thanks guys for the info. Of course some engines may well run fine without a speed sensor and that is indeed my experience. However, this time, I am mindful of the fact that Land Rover never fitted bits if they could possibly get away with not fitting them. In this case, they felt it necessary to supply a speed sensor signal to the ECU.
So in this installation I would like to do likewise.
So back to my original question, would the YBE100530 transducer send a suitable signal to the 14CUX Ecu ?
Mo
So in this installation I would like to do likewise.
So back to my original question, would the YBE100530 transducer send a suitable signal to the 14CUX Ecu ?
Mo
