Anyone's Tachometer Ever Mess up?
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Post Fiend
Joined: Jul 2005
Posts: 14,582
Likes: 12
From: 21791
Anyone's Tachometer Ever Mess up?
Today i was hauling logs all day long with the 07 F-550.... On the way back to the shop, the town ended and speed limit opened up, i went to accelerate like i normally do, and saw the tach was only at 1200rpm, in OD at about 45 mph. Truck was pulling hard, i was thinking that this truck never had this much huevos at this engine speed, whats up? With the 4.88 rears, it should spin 2000 rpm at 53mph, and at 45mph in OD it SHOULD be around 1700. My first instinct was that the transmission had found another magical gear which was like a super-overdrive, but when i floored the pedal i could hear the engine spin up well over 3000 but the tach only showed 2200ish. Pulled over and the idle speed brought the tach right below 0, which that in itself is pretty freaky. Shut it off, and started back up, and all was fine. Anyone else ever have this probem? 
Posting Guru
Joined: Jan 2003
Posts: 2,181
Likes: 3
From: Eastern CT.
My tach on my 06' F-350 6.0 had one weird day,,but my tach was showing about 800 RPM to high,,at idle around 1,500 rpm,,at 55 mph was reading 2,300 rpm,,with 3:73, 55 mph should be around 1,400 or so, in OD, when I shut it down, tach was reading about 800 RPM,,truck off !!
Later the same day drove the truck, shut it off, tach was lower,,on and off a few times,,then it dropped to zero,,has been OK since,,everything else worked fine.
We will see if it happens again. Later,,,,Mark
Later the same day drove the truck, shut it off, tach was lower,,on and off a few times,,then it dropped to zero,,has been OK since,,everything else worked fine.
We will see if it happens again. Later,,,,Mark
Postmaster
Joined: Dec 2003
Posts: 4,196
Likes: 10
From: Arizona
Here is the TSB on the problem, can be caused by a bad Cluster, ABS Module, ABS Speed Sensor, Vehicle Wiring
http://www.ford-trucks.com/tsb/fullt...php?tsb=06-7-4
http://www.ford-trucks.com/tsb/fullt...php?tsb=06-7-4
Mountain Pass
Joined: Oct 2004
Posts: 186
Likes: 1
From: New Mexico
My '05 had both the speedometer go to 0 and the tach read way off as you stated. This only happened one time, and over a year and a half ago. I had just finished moving a fifth wheel trailer fo a guy, about 16,000 pounds. I would never have agreed to take it where he wanted it if I had seen the area before hand. Very sandy, I was in 4 Low and given' her hell to get the trailer where he wanted it. I assumed the excessive wheel spinning had afected the ABS sensor somehow, no idea why the tach was off. I stopped the truck, shut it down, waited about 30 seconds and fired it up. Everything went back to normal and I now have about 77,000 miles on the clock. Never saw the problem again.
