Crazy Speedo..
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Freshman User
Joined: Jan 2007
Posts: 25
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Crazy Speedo..
Ok all. 1990 F150 XLT Lariat,AT,5.0L 153,000 mi.. I bought this truck for $1200 3 weeks ago and aside from replacing the battery and the alternator she is STRONG !!! My problem is when it is cold the speedo will start out telling me I'm running like 80+ mph when I know by tach I'm only running 65. Set the cruise at 70(using tach)and as the truck gets warm the speedo slowly falls to close to the speed I'm running. Oh BTW it has 215's instead of 235's on it but its still nowhere close to accurate. Also(as if this wasn't enough)my cruise will gradually increase rpm's over the course of 10 to 15 miles by about 50 to 100 rpm.
Thank You for your time and Talents !!!!
Troy with his new Toy
Thank You for your time and Talents !!!!
Troy with his new Toy
Elder User
Joined: Oct 2004
Posts: 626
Likes: 0
Yes. did my son's and cost $20. for the sensor. Also had the abs light on checked the brakes and they were good. Repaced the sensor and speedo is fixed and abs light went out. Took 5 minutes to do. Only 1 bolt and the 2 wire plug. It's right on top of the pumkin, you can't miss it!
Elder User
Joined: Nov 2006
Posts: 614
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From: Pensacola, FL
a 90 model should still be a mechanical speedo, i thought. the cruise problem is a result of the speedo not working properly as that is how the computer knows when to give it more or less gas to maintain certain speed. first thing to figure out is whether you have mech. or electric speedo.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Originally Posted by dslmechanic
speed sensor in the rear differential located on the top is going bad and will need to be replaced.
A 1990 doesn't have a VSS. It uses a mechanical speedo - regardless of what transmission he has.
To the OP: are you sure your tranny isn't slipping? The cruise slowly speeding up usually means a vacuum leak - I *think* the 90 F-150 has a mechanical cruise control, not electronic.
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Elder User
Joined: Nov 2006
Posts: 614
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From: Pensacola, FL
i know an 89 model has electronic sensor on the speedometer going into transmission for the cruise control.
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Brett Foote
Elder User
Joined: Nov 2006
Posts: 614
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From: Pensacola, FL
two wires connecting to the speedo at the transmission, where the cable screws onto the transmission there is a a two prong electrical connection, was on mine anyway. i was told it was for the cruise control.
Post Fiend
Joined: Apr 2004
Posts: 6,473
Likes: 4
From: Lafayette, IN
My '90 had a mechanical speedo and cruise control, and there were no wires to the tranny other than the neutral safety switch. The speedo cable was all by its lonesome, no wires with it.
Jason
Jason
Senior User
Joined: Feb 2005
Posts: 200
Likes: 1
From: Chester County PA
92 and up uses the vss for the spedometer. Older than that reguardless of tranny its a mechanical speedo. Find a gauge cluster on ebay or one a junk yard and that should fix the problem. U can find them pretty cheap. Good Luck.
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