Duratec misfire,Speedo dropping to zero when brake pedal is pressed

[Tonmawrie]

Hi looking for help with the above. Car has developed an intermittent misfire, seems to be affected when electrical circuits are activated, is indicators put on etc, also when the brake is pressed, this also makes the Speedo stop reading. Just wondering if it's a common fault before I start pulling it to bits.

thanks in advance.

[SM25T]

Look for a loose earth.

[Jonathan Kay]

As Ian says. Check all of your battery and engine and instrument earths: inspect, wiggle, disconnect, clean, reconnect.

Speedo driven off the rear wheel?

Has it ever blown any fuses?

Can you make the fault occur at will in the garage?

Do you have a multimeter and an appropriate wiring diagram?

Jonathan

[John Vine]

Agree about checking for poor earths.

... this also makes the Speedo stop reading.

That could well be caused by the sender circuit picking up stray induced currents.  For a fix, have a look at the Speedometers technical guide.

Btw, what year is your car?

JV