Speedo Doing 40MPH In Park.

[kcb905]

Have a 94' with a 5.7ltr.

Went out and started the tuck after a week of sitting and noticed the speedo doing 20 to 40mph at idle, in park. (No previous problems)

I didn't touch the gas but, the speedo gains/loses MPH if I increase/decrease the speed of the heater blower.

What gives?

 

[Erik the Awful]

Check your grounds. That sounds like something's backfeeding power to your speedometer.

 

[kcb905]

That's interesting. Thank you. Could it be tied into the ignition switch cylinder? I really have to force the key to get this thing to turn over and it doesn't always catch. (Waiting on a replacement in the mail at the moment)

 

[GoToGuy]

Key tumbler and ignition switch are two different parts.

 

[DerekTheGreat]

2nd the ground check. My speedometer and tach began to twitch whenever I used my turn signal. I cleaned up the grounds (located under the dash right around where you left knee would be while sitting) and that went away.

 

[kcb905]

Thanks, I'm going to dig around under there. Seen a few mentions of that spot before.