Fluctuating speedo
Discussion
My 94 4.0 with LCD mileage window and no trip has a weird problem. I appear to get a correct speed reading when I am on the throttle but as soon as I back off, even if only partially, the needle drops back by about 30 - 40 mph. When press on throttle again it comes back to correct speed.
I guess its something to do with the ECU as it's pedal position related, anyone any ideas as to where I should look to try and fix it as I have an MOT due...
I guess its something to do with the ECU as it's pedal position related, anyone any ideas as to where I should look to try and fix it as I have an MOT due...
Hi
Could be the gap on the sensor wants adjusting at the diff.
Adjust gap with feeler gauges to about 10 thou' and make sure the sensor doesn't touch the
toothed wheel when rotated by hand.
Sensor looks like a big thick brass bolt with a wire comming out at one end about 4 iches long.
On the other hand the sensor might be knackered as they are not known for their reliability. Cost about 40 quid from TVR.
As yours is an earlyish car the sensor may be mounted on the diff input shaft (ie the propshaft) on mine however it was on the half shaft ouput flange.
The idear is the same in that the sensor is mounted very close to a toothed wheel on the half shaft or propshaft and the sensor counts the number of teeth that pass it per second and from this work out your road speed. If the sensor gets dirt on it, between it and the teeth this can lead to spurious readings as can an incorrect gap setting.
So check there's no muck at the end of the sensor, check the gap is 10 thou' ish.
If all OK but still does'nt work then replace the sensor.
Relaced mine 3rd week of ownership if thats any consolation.
Cheers
Paul
Could be the gap on the sensor wants adjusting at the diff.
Adjust gap with feeler gauges to about 10 thou' and make sure the sensor doesn't touch the
toothed wheel when rotated by hand.
Sensor looks like a big thick brass bolt with a wire comming out at one end about 4 iches long.
On the other hand the sensor might be knackered as they are not known for their reliability. Cost about 40 quid from TVR.
As yours is an earlyish car the sensor may be mounted on the diff input shaft (ie the propshaft) on mine however it was on the half shaft ouput flange.
The idear is the same in that the sensor is mounted very close to a toothed wheel on the half shaft or propshaft and the sensor counts the number of teeth that pass it per second and from this work out your road speed. If the sensor gets dirt on it, between it and the teeth this can lead to spurious readings as can an incorrect gap setting.
So check there's no muck at the end of the sensor, check the gap is 10 thou' ish.
If all OK but still does'nt work then replace the sensor.
Relaced mine 3rd week of ownership if thats any consolation.
Cheers
Paul
Hi,
had exactly the same problem with my Griffith 500 (94, LCD odometer, T5 gbox). Found the gap between the speedo sensor and toothed wheel on the diff nose was way to big. Problem was there was no more adjustment as the sensor was screwed all the way into the bracket. I just bent the bracket down until the gap was as small as possible without it catching on the toothed wheel, problem fixed.
Ozstyle
had exactly the same problem with my Griffith 500 (94, LCD odometer, T5 gbox). Found the gap between the speedo sensor and toothed wheel on the diff nose was way to big. Problem was there was no more adjustment as the sensor was screwed all the way into the bracket. I just bent the bracket down until the gap was as small as possible without it catching on the toothed wheel, problem fixed.
Ozstyle
Mike, I agree with the other two replies but there are a couple of points here.
I have looked at the Bible and it says that the change over year from the Rover SD1 to the Borg Warner T5 gearbox was 1994, the year of your car.
The difference is easy to accertain if you don't already know, the reverse on the SD1 box is top L/H side, on the later T5 box it's below 5th.
The point is that the Bible says that on the SD1 box the speedo sensor is fitted to the gearbox (LHS if I remember correctly).
Early T5 it's a sensor above the propshaft UJ at the diff end, and later cars it's a sensor and toothed wheel located on the differential half shaft.
It also says that it can be caused by an intermittent sensor connection, or a dity sensor tip.
I surmise that wear causing back lash could be the problem, i.e. the gap between the sensor and the toothed wheel could vary because of this, leading to the fluctuation whether the engine is driving the wheels or vice versa.
If this is the cause careful adjustment of the sensor should cure it.
I hope this is of help to you
I have looked at the Bible and it says that the change over year from the Rover SD1 to the Borg Warner T5 gearbox was 1994, the year of your car.
The difference is easy to accertain if you don't already know, the reverse on the SD1 box is top L/H side, on the later T5 box it's below 5th.
The point is that the Bible says that on the SD1 box the speedo sensor is fitted to the gearbox (LHS if I remember correctly).
Early T5 it's a sensor above the propshaft UJ at the diff end, and later cars it's a sensor and toothed wheel located on the differential half shaft.
It also says that it can be caused by an intermittent sensor connection, or a dity sensor tip.
I surmise that wear causing back lash could be the problem, i.e. the gap between the sensor and the toothed wheel could vary because of this, leading to the fluctuation whether the engine is driving the wheels or vice versa.
If this is the cause careful adjustment of the sensor should cure it.
I hope this is of help to you
Gassing Station | Chimaera | Top of Page | What's New | My Stuff