What controls the speedometer?

[beatboxer13]

What controls the speedometer?

Reason:

At random times my speedometer will jump up and return back to normal. This only happens under acceleration in mid-release of clutch.

Weird eh?

[Lancer211]

Obviously we're talking about a MTX rather than an ATX, right?

[FordFociSHO]

The ECU controls the speedometer technically via a signal from the Vehicle Speed Sensor on the back of the transmission.

Your problem though is a poor ground or a ignition misfire. Both will make the speedometer act funny (only the speedometer though, never have figure why just though). Clean the grounds and make sure they are tight. Check the plug wires for signs of arcing (white marks), the spark plugs for damage (cracked porcelain?) and the ignition coil for any cracks. Best ways to check for ignition problems are at night or in a very dark area or with water in a spray bottle.

[beatboxer13]

Originally Posted by FordFociSHO

The ECU controls the speedometer technically via a signal from the Vehicle Speed Sensor on the back of the transmission.

Your problem though is a poor ground or a ignition misfire. Both will make the speedometer act funny (only the speedometer though, never have figure why just though). Clean the grounds and make sure they are tight. Check the plug wires for signs of arcing (white marks), the spark plugs for damage (cracked porcelain?) and the ignition coil for any cracks. Best ways to check for ignition problems are at night or in a very dark area or with water in a spray bottle.

Thank you for your awesome reply!

Which grounds should I be checking? I am super unfamiliar with the focus's electronics.

And with that said, the ignition is also part of the electronic system lol, so here are 2 pics of my plugs situation:




Not sure what that brown dust it, but its only in boot #4. I did a bit of research and determined that brown dust was not an issue. Is that true?

[FordFociSHO]

The brown dust thing you found is more than likely a duratec specif problem (I know there was a red dust issue while back, I think). Anyway, the dust on yours is from water sitting in the plug well and evaporating, dust is the residual minerals/contaminates in the water. So long as there is no water down there it shouldn't be a problem, can't rule out corrosion inside the boot though (some wires you can push the plug wire out of the boot to have a look, some are glued in, basically at your own risk kind of deal).


The plugs look decently worn and about due for a change. IMO stick with Motorcraft or Autolite brands (seems to always be someone with an issue when they change to a different brand).


Far as what grounds to clean/look at. Easiest way for me to tell/show you is to tell you to search for threads relating to "the big 3". In a nutshell though, clean the battery terminals, the grounds on the drivers fender (just below the washer fluid fill) and the main ground on the transmission (just behind the coil and about straight down from the EGR mess).

[G-forces]

Don't forget the bridge from the strut tower to engine hanger, by the power steering bottle. And you can run a 4 gauge cable from the battery to the front hanger for even better grounding.

[beatboxer13]

thanks everyone!!