hi this is my first post as have just become a very happy owner of a 300 but i have one little problem i hope someone can shed some light on its with the speedo it an itermitent fault some times it works most of the time it doesnt but even when its not working the trip clock still works and also when its not working i cant boot it hard as it hits like a rev limiter around 4500 rpm and if i back off slightly and ease back on the pedal it will pull straight through past 4500. My car is a 1990 turbo auto import i disconected the gizmo on the back of the dash that converts it to mph as i read that this can cause the problem but this made no difference the other thing that i hear can cause this fault is the speed sensor on the box this looked new on my box as it had a referbished box fitted 11 months ago but what is puzzeling me is that the trip clock works all the time which to me would sugest that the speed sensor is working unless there is another sensor that i dont know about if there is'nt then i would have put the fault down to the dash but i dont see how this could cause a problem when i boot it, if anyone can point me in the right direction as to what could be causing the fault i be very greatfull as its doing my head in.

When the speedo stops does the steering go heavy?

not that i have noticed but i will check this morning

It's not your speedsensor.

the speedsensor signal goes directly to the speedo dial and the electronics in the dial convert the signal into a pulse signal which is then send to all ECU's

 

The main engine ECU needs the speed signal otherwise a 4400 rpm revlimiter and some other limiters are activated, as the ECU thinks the car is standing still.

 

In a lot of cases the cause of non or intermittent working speedo's is caused by tiny cracks in the solder joints on the speedo board.

Resoldering the joints solves the problem (in most cases)

How easy is it to remove the speedo head and access the area needing soldered?

 

My speedo cuts out randomly, causes the power steering to cutout as well.

It's dead easy to get to, just remove the 2 screws from under the hood over the dials then unscrew the gauge unit and unplug the wires.

Can't remember if you have to take the 2 side pods off as well but they just screw in from underneath too.

Then there's just a few screws to open up the unit and access the speedo.

10 minute job :)

It's not your speedsensor.

the speedsensor signal goes directly to the speedo dial and the electronics in the dial convert the signal into a pulse signal which is then send to all ECU's

 

The main engine ECU needs the speed signal otherwise a 4400 rpm revlimiter and some other limiters are activated, as the ECU thinks the car is standing still.

 

In a lot of cases the cause of non or intermittent working speedo's is caused by tiny cracks in the solder joints on the speedo board.

Resoldering the joints solves the problem (in most cases)

 

 

 

 

thanks very much for that i will whip the clocks back out, i favour that idea coz i cant see what else it could be especially as the distance clock still goes up when the speedo is not working which surgested to me the speed sensor is working and the signal is getting to the circuit board on the dash working the trip clock but not getting to the speedo