Speedo problems

[pbaker43]

The speedo decided to go into mental mode whipping from 0 to 180 and anywhere in the middle, it has done it before and then stopped, but this time the speedo stopped to move, I cleaned the sensor and re-gapped it to 5 thou from the wheel worked like a dream until I floored the engine the needle flew around the clock and then rested at zero,
Any ideas anyone.?

[spend]

Infamous splitter box?

[pbaker43]

Spend - what is the 'splitter box' and where can I find it, I hope it is not going to cost a fortune

[spend]

Under the dash, splits the signal from speedo sensor to speedo & ecu on later cars. I suppose you could just remove it to test ~ removing the speed input from ecu stepper control might even be an improvement anyway?

[MikeTVR]

spend said:

I suppose you could just remove it to test ~ removing the speed input from ecu stepper control might even be an improvement anyway?

The splitter is important to the operation of the ECU so don't remove it. I can only speak for my '94 model - it's not so much a splitter as a constant pulse rate out to the ECU when road speed is at anything above about 3mph. This signal is required by the ECU to tell it when to adjust the idle speed and when not to. The constant pulse rate out probably prevents the ECU from going into speed limit.
The signal wire from the road speed sensor merely goes to this so called 'splitter' AND the speedo. I would prefer to call it a signal converter or speed converter.
Mike

[shpub]

Is this with the sensor on the diff trigger wheels?

If so I reckon you've taken out the sensor when you booted it. Under such conditions it is not uncommon to see trigger wheel run out of 30-50 thou caused by slight movement of the o/p shaft under load. If there is only a 5 thou gap, I suspect the the trigger wheel may have become intimate with the sensor causing a spiky signal (and 180 mph) before killing it and a zero signal.

[Chimpafrolic]

spend said:

Under the dash, splits the signal from speedo sensor to speedo & ecu on later cars. I suppose you could just remove it to test ~ removing the speed input from ecu stepper control might even be an improvement anyway?

Many of your points are to say 'pointless'...

The "Infamous Splitter Box" more accurately described as the "ECU Speed Signal Unit" just converts a signal from the speedo head into something the ECU can interpret.

It would be highly unlikely that the "ECU Speed Signal Unit" would send a back feed to the speedo head causing the needle to shoot round to 180mph.

In reality if the ECU is not picking up a signal from the "ECU Speed Signal Unit" the outcome will be poor or ineffective idle control.

This typically happens when you come off a motorway slip, if you have to completely stop at the junction the car will likely stall.

But we a getting distracted here.

The problem pbaker43 describes is far more likely to be either a fault with the speedo head itself or the sensor.

My money would be on a faulty speedo.

Here is a useful device from Steve Heath that allows both the sensor and the speedo head unit to be checked.

https://delta.securesslhost.net/~shenglt/catalog/p...

As always intelligent diagnosis will always beat ill informed guess work.

[Chimpafrolic]

Philip, if it turns out the sensor is at fault the the sensor/diagnostic kit from Steve Heath should also fix the problem.

If you find your speedo needs reconditioning these people will sort it.

http://www.etbinstruments.com/

Good luck with it mate, let me know how you get on.

[spend]

Funny you think the ECU speed sensor is critical, when many such as Pete Humphries have long advocated disconnecting the stepper motor completely. As I understand it the speed sensor only really affects ecu mapping for the idle control, and most are actually trying to make the stepper stop interfering when on the move?

[pbaker43]

Hi Dave
Thanks for the intelligent answer, the solution from Steve Heath looks ‘the dogs back wheels’ no more messing around repair once and forget… The car is off the road as the snow is starting to fall in the mountains, plus I am a bit fed up lying on the floor, so I will finish the cleaning and renewing bits in the engine department first, then get down to this sensor, at least I know the direction to go.

[TvrToe]

I replaced the speed sensor too, before I found a loose connection on the rear of the speedo. The terminal nut had been lost and the ring crimp on the end of the signal wire was simply resting on the terminal post. Speedo jumped all over the place. Simple as that!

[Chimpafrolic]

TvrToe said:

I replaced the speed sensor too, before I found a loose connection on the rear of the speedo. The terminal nut had been lost and the ring crimp on the end of the signal wire was simply resting on the terminal post. Speedo jumped all over the place. Simple as that!

Now that sounds like a highly plausible cause of the OP's problem

I had the stalling at junctions thing, for this fault most will immediately point you to the stepper motor.

But in my case it also turned out to be a bad connection at the speedo.

Philip, in view my and TvrToe's experiences I would get the dash top off & check all the speedo connections before you go spending on new parts.

[pbaker43]

Nice one guys, I will check the connections on the speedo.

I did notice yesterday while out for a spin (before stripping the engine) the speedo rested at zero but the engine did not cut out when i came to a junction and it ticked over at 900 rpm with the odd flutter..