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Topic: VSS problem (Read 3348 times) |
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andyg66
Newbie
2.0 16v ultima saloon '96'
Posts: 21
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Re: VSS problem
« Reply #20 on: May 5th, 2010, 8:12pm » |
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Hi Ray, Sorry to bova you again but I found out the reason why AVC wasn't working properly was because it was on low turn it up and it was fine. I tested my cruise control that was fine 3mins after I turned it off my speedo dropped to 0, the gear box dropped down to 1st, the cruise control wouldn't work, the AVC wouldn't work, wouldn't go up to 2nd 3rd or 4th. I pressed the snow button to try and force it into 2nd but that didn't work. I stopped the car, all I had was 1st and reverse. Started to drive in 1st and after 10mins the speedo started to work again and my gears began to work. What I need to know is this wiring problems or do I need to put a new VSS in. :/ Andy
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Cosray
Full Member
8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: VSS problem
« Reply #21 on: May 5th, 2010, 8:56pm » |
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[quote] Vehicle Speed Sensor
The VSS is driven by a tachometer drive in the transmission and uses the Hall effect to provide a digital voltage signal to the PCM, which assigns a corresponding vehicle speed to the signal. With other inputs, the PCM uses this to calculate idle speed control, fuel enrichment during deceleration, and cuts off fuel supply on closed throttle deceleration at speeds greater than 1800 rpm and 5mph.
An example of the way in which integration between different vehicle systems is increasing is by considering this VSS signal. As well as providing vehicle speed information to the PCM, the same signal is used by the electronic Instrument cluster to display the vehicle speed, by the Trip computer to calculate distance and speed, by the speed-sensitive power steering to reduce steering assistance and by the cruise control system. The VSS signal is also used by the radio for the Automatic Volume Control if the option is present and turned on.
In an automatic Scorpio the PCM uses the VSS as an input for the control of line pressure, gear shifts and the engagement of the torque converter clutch and compares the VSS sensor data with that of the TSS to control slip. Monitored by: CCM
This is undoubtedly why the Hall efect was chosen rather than the Inductive pulse generator used on the CKP and the CMP.
Fault Symptoms: harsh engagement, difficult engagement - sudden downshift when throttle is closed - torque converter clutch fails to engage
[end quote]
The VSS is a semiconductor device which, as a binary device, either works or does not. It may fail erratically though. Replace by new in all cases.
It receives its induction signal from a cogwheel which may fail or jitter or swing mechanically. Please check tolerance, play, loseness etc.
Once you are operating in that area you have to be deductive in a very systematic way.
You probably need to lift the car anyway in order to get to the VSS area. Follow the loom.
Wiring plays a major part in getting its relatively small signal across to all related components. Check wiring thoroughly; highly suspect in todays Scorpios since the youngest Scorpio specimens are now over 12 years old... I am being very pessimistic, yes, by experience.
This means inspecting the loom wire by wire and strand by strand visually. What happens is that in hot and vertical areas the wires' isolation becomes brittle, isolation drops down, bare strands erratically touch and cause unpredictable and strange effects. Not shorting, not smoke, not blown fuses - just very confused signals causing erratic behaviour, as you experience.
Also the main engine compartment loom again is the usual suspect, regardless model. Each and every small control singnal has to pass through those old and tired wires and connectors.
HTH
Ray
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andyg66
Newbie
2.0 16v ultima saloon '96'
Posts: 21
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Re: VSS problem
« Reply #22 on: May 5th, 2010, 9:06pm » |
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H i Ray, Thank you very much I will put the car on ramps at weekend, check all wiring. I don't suppose you know the part number for the VSS 2ltr 16v. Once again thank you very much your advice has been really helpful.
Andy
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andyg66
Newbie
2.0 16v ultima saloon '96'
Posts: 21
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Re: VSS problem
« Reply #24 on: May 5th, 2010, 9:49pm » |
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Thanks again Ray the links will be helpful 
Andy
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tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
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Re: VSS problem
« Reply #25 on: May 6th, 2010, 7:44am » |
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on May 5th, 2010, 9:06pm, andyg66 wrote:H i Ray, Thank you very much I will put the car on ramps at weekend, check all wiring. I don't suppose you know the part number for the VSS 2ltr 16v. Once again thank you very much your advice has been really helpful.
Andy |
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The finis is 1021991. It's the same for all models with autobox, only the pinion is model specific. Note that don't worry if your old one is metallic and the new one is plastic, the pinion and it's clip are 100% interchangeable, you just move them.
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