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Windy101
Silverstone


Joined: 05 Jun 2015
Posts: 103



PostPosted: Mon Jul 31, 2017 4:04 pm    Post subject: 993 oil level gauge issue Reply with quote

My oil level gauge seems to have stopped working. I know there is a lot of mis-understanding regarding how these work and I know the car should be hot and idling and on a level surface to get a reading.

What I know.

My in tank sender does read appropriate resistance values when moved manually (removed from tank) - so the sender is fine.

I get continuity when testing from engine bay connection to gauge, so its not open circuit.

Gauge never moves and always sits at the bottom, empty(not enough oil).

If I do not connect the oil gauge side of the gauge the fuel gauge does not work.

A new wire was run from fuel gauge to fuel level sensor to resolve an intermittent open circuit on fuel gauge, some time ago - could this be causing the problem?

Any ideas before I buy a second hand gauge which may or may not resolve the issue?

Any idea on how to trouble shoot the gauge itself?
 
  
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Zorro
Monza


Joined: 05 Oct 2014
Posts: 154
Location: East Sussex


PostPosted: Mon Jul 31, 2017 5:07 pm    Post subject: Reply with quote

I assume you have enough oil in the sump to register.
 
  
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Windy101
Silverstone


Joined: 05 Jun 2015
Posts: 103



PostPosted: Mon Jul 31, 2017 5:11 pm    Post subject: Reply with quote

Zorro wrote:
I assume you have enough oil in the sump to register.


Definetely.

When I remove the float from the oil tank and move it up and down I can see the resistence change with a meter, but the gauge does not move.
 
  
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madalaa
Yas Marina


Joined: 13 Mar 2008
Posts: 8768
Location: West London

1995 Porsche 993 Carrera 4

PostPosted: Mon Jul 31, 2017 5:32 pm    Post subject: Reply with quote

A new wire was run from fuel gauge to fuel level sensor to resolve an intermittent open circuit on fuel gauge, some time ago - could this be causing the problem?

....... that would be my first port of call ........
 
  
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Windy101
Silverstone


Joined: 05 Jun 2015
Posts: 103



PostPosted: Mon Jul 31, 2017 10:43 pm    Post subject: Reply with quote

madalaa wrote:
A new wire was run from fuel gauge to fuel level sensor to resolve an intermittent open circuit on fuel gauge, some time ago - could this be causing the problem?

....... that would be my first port of call ........


I agree, does anybody have any idea how to test the gauge in isolation?
 
  
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9xxnick
Silverstone


Joined: 29 Jul 2014
Posts: 122



PostPosted: Mon Jul 31, 2017 10:47 pm    Post subject: Reply with quote

I'd be looking to check if there's any voltage at the gauge. I'm not certain for 993 gauges, but the normal mode of operation is for the gauge to be supplied with 12V and the "earth" side to be connected to the sender. If there's 12V at the gauge then connecting the other side of the gauge direct to earth should give full-scale deflection (i.e. maximum reading). If there's voltage and earthing doesn't have this effect then you've likely got a defective instrument.
 
  
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madalaa
Yas Marina


Joined: 13 Mar 2008
Posts: 8768
Location: West London

1995 Porsche 993 Carrera 4

PostPosted: Tue Aug 01, 2017 8:05 am    Post subject: Reply with quote

Hopefully Tore B will pop in soon and see this thread as I am sure he will be able to point you in the right direction and help you find the cause.
 
  
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ras62
Montreal


Joined: 20 Jan 2012
Posts: 571
Location: Cheshire


PostPosted: Tue Aug 01, 2017 10:33 am    Post subject: Reply with quote

It sounds like you have an earth problem. The most likely culprit is the central electrics earth (this is used by both fuel and oil level gauges). The earth connection is a brown 0.5mm2 cable and connects to the inner wing area iirc. Description on the elec schematics says Central Electrics on side member right. This is for a 964 but the 933 should be the same.
Other earth to check is right side of the engine bay. Not so easy to see down there on a 993.
 
  
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Windy101
Silverstone


Joined: 05 Jun 2015
Posts: 103



PostPosted: Tue Aug 01, 2017 1:10 pm    Post subject: Reply with quote

9xxnick wrote:
I'd be looking to check if there's any voltage at the gauge. I'm not certain for 993 gauges, but the normal mode of operation is for the gauge to be supplied with 12V and the "earth" side to be connected to the sender. If there's 12V at the gauge then connecting the other side of the gauge direct to earth should give full-scale deflection (i.e. maximum reading). If there's voltage and earthing doesn't have this effect then you've likely got a defective instrument.


The gauge is getting voltage as the fuel gauge side is working, or are there 2 different supplies?

Also same with the earth, would they share the same earth?
 
  
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ras62
Montreal


Joined: 20 Jan 2012
Posts: 571
Location: Cheshire


PostPosted: Tue Aug 01, 2017 10:11 pm    Post subject: Reply with quote

The two gauges use the same earth mentioned earlier close to the cemtral elecrics compartment. I suspect from the mod to the fuel sender this has clouded the issue. The earth for the oil sender is inside the right hand side of the engine compartment, again as mentioned in my other post.
 
  
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9xxnick
Silverstone


Joined: 29 Jul 2014
Posts: 122



PostPosted: Fri Aug 04, 2017 7:14 pm    Post subject: Reply with quote

I think there's some confusion between the earthing of the gauge itself, which is required for (e.g.) warning lights in the gauge to operate and the path the current takes through the gauge and then to earth via the oil level sender.

Given that you seem to have continuity from the gauge connector to the level sender in the tank, have you considered just connecting this connection to earth directly, bypassing the sender? If the instrument is actually getting 12V this should result in full scale deflection of the needle. If it doesn't you probably don't have 12V to the actual gauge or the gauge itself has failed.
 
  
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