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Registered
1985 500sel and 500sec 2012 E63 1989 Porsche 911
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5,241 Posts
Discussion Starter #1
out of the blue, my gas gauge has started to act wierd. when i fill up the car, the needle doesnt go all the way to the full side end. and now the yellow light goes on when the needle is at quarter. before it would go on at 1/8th. i get about 320 miles on the trip when thelight goes on and i get about 15mpg, used to be 17 ( not bad for a 500sel?)

so what could cause it get shifty like this

another thing is the speedometer seem like a from 75mph and onward, it is way off. it speeds up from 80-100 as if im in a e55amg. when im doing "100mph" the car is barely passing a minivan inthe next lane.

Below 75 speeds seem normal, doesnt feel faster/slower than it states

so if a speedo is miscalibrated can it occur at specific ranges or throughout the whole range

wheels/tires are stock
thanks
 

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1991 300 SE
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18,534 Posts
Sounds like the fuel-sending unit has gone ‘haywire’ – literally.

Most often the fix is to replace the unit but some have had success pulling the unit from the top of the tank (driver’s side LHD, passenger side RHD) cleaning or replacing the wires and connections. They become dirty and corroded over the years, which interferes with the electrical signal.

BTW, I experimented with my 500 SEL and did not exceed 60 mph on a recent trip back home. 438 miles, 18 gallons of fuel, 24 mpg. It’s the speed, man, it really sucks up the fuel. Granted, I was being passed by everything on the road including RVs towing SUVs – but an interesting experiment none the less.
 

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Registered
1985 500sel and 500sec 2012 E63 1989 Porsche 911
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5,241 Posts
Discussion Starter #3
60mph, i could never stay that slow, LOL.

Ill check those wires, though im not 100% sure what they look like.

the speedo thing is whats really wierd though. I heard speedo service can cost a few hundred bucks, so im probably going to leaveit well alone, but it just seems odd
 

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Moderator
1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,291 Posts
Hi vdubpower,

I'm with jdc on the fuel sender as the likely culprit, having experienced those corroded wiring issues on a couple of teenaged cars in the past. Different manufacturer, similar problems though.

That said, I'd toss that probability if the fuel gauge and the speedometer started to malfunction at once, together.

[:)] MBL
 
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