North American Turbocoupe Organization



Speedo dies out eventually
philS Offline
Senior Member
#1
I'm having an intermittent problem with the speedo (car is 86 TC with the analog speedo, VSS, w/o speedo cable). After an hour or so of driving, it will start to drop 5 mph, then go right back up. Then after 10 minutes more, it starts dropping to zero then back up. Then it becomes more erratic. Then it dies. (Other gauges working ok, except for the gas gauge which has always been boned).

Next time out, works fine for an hour or so, then the same deal.

As a side note, last year the VSS shaft was bent, and the sensor would vibrate itself out of the transmission and the speedo would stop working. I replaced it w/ a JY shaft and all was well. I suspected the same thing this time, but this morning I crawled under there before work and the speed sensor is still in place.

So what do you think it could be?

- Electrical (hope I don't have to trace a bad wire back to the computer [Image: biggrin.gif] )
- Sensor going bad
- Heat soke
- Bad connection on the back of the gauge cluster

Thanks for any advice! I've been absent from the board for the last 6 months ... busy with work and not driving much.

Phil
Did you hear about the Lucas powered torpedo? It sank.

86 TC, 73 Mini, 64 Mini Van, Saturn wagon
Click here to beat a ricer.
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segfaultxr7 Offline
Posting Freak
#2
If the cruise works while it's reading 0 mph, it is a speedometer problem. Does the odometer continue to run?

Otherwise, it sounds like a VSS failure, that's what they typically do when they go bad.
88 TC 5-speed
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philS Offline
Senior Member
#3
Thanks.

Unfortunately, my cruise hasn't worked for months ... and I have yet to fix it since I never use it!

Have you had any luck with junkyard VSS's? I got a quote from Ford - they said around $60 for a new one.

I wonder if there's any way to test the sensor on the car? How about putting the rear end up on jackstands, attaching a multimeter to the VSS wires, and running her through the gears [Image: biggrin.gif]

Seriously - do you think there's any way to remove the sensor from the transmission, and turn the sensor shaft by hand to see if it registers properly? Maybe use a drill to speed it up (on low, of course)?
Did you hear about the Lucas powered torpedo? It sank.

86 TC, 73 Mini, 64 Mini Van, Saturn wagon
Click here to beat a ricer.
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Jeff K Offline
Administrator
#4
You can measure its resistance, which should be 200 ohms. You can also verify this with a KOEO test, which will throw a code if the VSS resistance is out of range.

To actually test it in operation, you need an oscilloscope, as the VSS output is a variable frequency signal.

As segfaultxr7 suggested, see if the odometer works when the speedo quits. If it does, the spedo is bad.

Do you have a trip computer? If you do, it also uses the VSS signal, so if the trip comp works, the VSS is good.

------------------
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 00 Windstar (wifes vehicle)
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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philS Offline
Senior Member
#5
thanks seg and Jeff,

the speedo continues to die out only after the transmission is hot (in traffic).

When it does, the odometer stops as well. i don't have the trip computer unfortunately.

Phil
Did you hear about the Lucas powered torpedo? It sank.

86 TC, 73 Mini, 64 Mini Van, Saturn wagon
Click here to beat a ricer.
Reply

philS Offline
Senior Member
#6
replaced the VSS and it's fine

Phil
Did you hear about the Lucas powered torpedo? It sank.

86 TC, 73 Mini, 64 Mini Van, Saturn wagon
Click here to beat a ricer.
Reply

Birdman78758 Offline
Senior Member
#7
Thanks for following up with solution, Phil!
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