Tachometer gone crazy!
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New User
Joined: Jan 2013
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Tachometer gone crazy!
Ok. Since I received some great help from my fellow ford truck enthusiasts I have another mystery. Recently purchased an 87 f250 4x4 inline six and the tach is not reading correctly. Would anyone know why? At idle its pretty close reading about 800 RPM, but when accelerating, it wraps all the way to red line, when in reality probably around 2500-3000 betweeen shifts. All ignition/coil/distributor wiring seems to be all good and it is an original tach that came with the truck. Any ideas would be helpful!
Thanks guys!
Thanks guys!
Fleet Mechanic
Joined: Nov 2011
Posts: 1,823
Likes: 43
From: New York
Often an erratic tach is symptomatic of a failing PIP or TFI, but usually it's more of a "bouncing" behavior than an "over-achieving" tach. Maybe your tach secretly wants to be attached to a 20,000 RPM red-line F1 engine? 
Any way, don't eliminate failing ignition components as a possibility, but it doesn't seem like the typical failure symptom.
Any way, don't eliminate failing ignition components as a possibility, but it doesn't seem like the typical failure symptom.
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
I'm guessing your tach is just basically shot. The tach in my '88 won't drop below 2200 when the engine is running and is about 1000 rpm too high in other situations. I think there a lot of the tachs in this vintage truck just shot.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
The tach in my '90 did the same thing, it's an easy fix just remove the bezel and glass from the front of the cluster, unplug the tach module and plug in another from a donor cluster of the same vintage.
Senior User
Joined: Apr 2003
Posts: 376
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From: Wanatah In,
I just had a similar issue with my tach, it ended up being cold solder joints. I actually just posted a video if you want to see if it may help you out. never mind that I sound like a dork.
Last edited by Tectron1; Feb 2, 2013 at 07:00 PM. Reason: moved video
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