Speed signal device

[jojackson4]

Were is it and what dose it look like as I think it's duff but nead to check its bits and bobs first
Thanks Peter

[Hoofa]

Its mounted on the diff looking at the gear ring on output on the diff, sensor needs to be gapped, check the gace of the senor is t damaged

[QBee]

What are your symptoms? No speedo no mileometer ? (yes, I know it's called an odometer)

[jojackson4]

No it's the ecu one not the speedo
Cocking out at comeing to a stop

[jojackson4]

Come on boys don't fail me 4 hours last night googling and I am no wiser my trust is in you

[QBee]

There was another thread touched on this about a weekm or two ago. I think t was when I commented that my idle was sticking at 1800 rpm when slowing down from quicker driving. I will check.

[QBee]

It's in the dash, behind the instruments, I think. Not sure what it looks like? I think blitz racing might know where it is and what it looks like

[Julesprivate]

There is a device behind the dash that changes the analogue speedo cable signal to digital and at the same time sends a signal to show the car is travelling at under 3 MPH - that signal is used to adjust the stepper motor to set the idle speed... Well more accurately it is used to set the stepper motor to open slightly on downchanges to help prevent locking the rear wheels - and as a added bonus give you the lovely popping and gurgling noise..but it also impacts the idle speed.

Is that the one you mean?

if your speedo stops working under 5-10MPH and then suddenly bursts into life that's normally the first place to look...

[Julesprivate]

Maybe if you describe the symptoms a little it'd help?

There is a speed transducer fitted, actually in different locations dependant on year of build. If yours is a T5 box it's either on the propshaft sensor ring or the diff. If it's on the diff there are 2 locations commonly used but both are pretty obvious (one requires propshaft removal to get to)..

[QBee]

Julesprivate said:

if your speedo stops working under 5-10MPH and then suddenly bursts into life that's normally the first place to look...

Mine does that. Nothing on the speeodo under 15-20 mph
I also have an issue with the idle when slowing from say 15 miles at 70 mph - the idle sticks at 1600-1800 rpm, eventually dropping back to 900 rpm

[Julesprivate]

QBee said:

Mine does that. Nothing on the speeodo under 15-20 mph
I also have an issue with the idle when slowing from say 15 miles at 70 mph - the idle sticks at 1600-1800 rpm, eventually dropping back to 900 rpm

I don't profess to (in any way) be an expert but I have been doing A LOT of reading on "common" issues since getting my Chimaera.

On later cars with a T5 box, behind the dashboard is a unit called a speedometer conversion/callibration unit which takes the transducer signal and "splits" it - one part going to the speedo, another to the ECU.

The signal to the ECU is "simplified" in that once the transducer shows a higher than 3MPH reading the callibration Unit sends a waveform to the ECU saying the car is actually doing ~36MPH, and that never changes (until the actual speed drops below 3MPH).

That signal is used by the stepper motor to control the idle speed, keeping it high between gear changes to smooth them and help prevent lock up on downchanges.

The poor old ECU has a bit of a hard time understand how the car manages to get from ~36MPH to zero so quickly and that seems to be part of the problem.

Have you cleaned your stepper motor and set the base idle recently?

You know (I'm sure) that you can run without a stepper motor if you disconnect it and set the base idle correctly. But that does create some other minor issues...

It's also worth understanding the part that the TPS plays in idle speed too, as either the TPS or Stepper (or stepper control) could cause that issue..

Edited by Julesprivate on Sunday 3rd March 22:56

[QBee]

Thanks Jules - seeing my TVR guy this morning, will discuss it with him.

[Dr Mike Oxgreen]

+1 for "nothing on the speedo below 15-20 mph".

Are we saying that's not normal?

[Julesprivate]

Don't know about "normal" but mine certainly works from just over zero up.. And on the way back down too.

i.e. if I am doing 5MPH my speedo shows that..

[jojackson4]

Julesprivate said:

There is a device behind the dash that changes the analogue speedo cable signal to digital and at the same time sends a signal to show the car is travelling at under 3 MPH - that signal is used to adjust the stepper motor to set the idle speed... Well more accurately it is used to set the stepper motor to open slightly on downchanges to help prevent locking the rear wheels - and as a added bonus give you the lovely popping and gurgling noise..but it also impacts the idle speed.

Is that the one you mean?

if your speedo stops working under 5-10MPH and then suddenly bursts into life that's normally the first place to look...

That's the one
The car stalls when coming to a stop not every time but very annoying it fires up no problem
I have 18 pages of setup for the ecu and one of the tests is on said speed signal device so I need to know what it looks like and I have the dash top off ready the speedo from memory is working ok
All ready found duff coolant sensor to say its a bit lazy is a under statement
Thanks Peter