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Location: Buffalo, NY
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Oil Pressure Gauge Problem

I posted once before and nothing seemed to work. I have been knocking off a couple very small gremlins and this Oil Pressure Gauge is still haunting me!

When I put the key in the ignition and turn the car to the on position the Oil Pressure Gauge pegs right to 5+ hard. The car is not even running. When I turn the key off AND tap on the dash the needle falls back to 0.

This gauge used to work just fine and then it started doing this a couple years ago. The car runs and drives great. It is also my DD.

The last post had some suggestions that it could be electrical. Clark's suggests a bad sending unit. I am assuming that when Clark's talked about a bad unit pegging at 5+ they mean when the car is running. BUT I disconnected both leads one at a time and then both at the same time and I still get the same result of the gauge pegging at 5+. I am guessing this has ruled out the sending unit as the problem. Correct?

I have the electrical schematics in my Haynes Manual (which seems useless).

I do not know what else to try or do. Any suggestions???
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'87 944 N/A (first Porsche)
'95 E-350 Diesel
'03 S-Type Jag 3.0
'03 Taurus SES
'06 Eddie Bauer Explorer

RIP SoCal
Old 08-05-2009, 12:55 PM
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In the Fires of Hell.....
 
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There are two wires going to the sender, a Blue-White one and a Blue-Red one.

The B/W one should go to the "G" location on the sender. It sends a voltage signal to the analog gauge itself.

The B/R one feeds the "Low oil pressure" Light, and should connect to the "Wx" post on the sender.

Having them switched can cause what you describe. If this is not the issue, then it is either the sender or the gauge itself. The wires go directly from the sender to the gauge, not through the DME or anything else.

Good luck, Keith
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Old 08-05-2009, 01:12 PM
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John, the oil pressure sensor acts like a variable resistor.
zero oil pressure should get around 10 ohms
5 bars should be around 170 ohms.

Disconnect both leads and measure the resistance with a meter. It should be around 10-20 ohms.
Testing at 5 bars of pressure will be a bit challenging. You will need air fittings and a regulated compressed air supply.

I don't think you can switch the wires, One terminal is a ring and the other is a spade, at least on mine.

PS. I will mail the toe tool tomorrow.
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Old 08-05-2009, 01:15 PM
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UPDATE:

Making some progress here! Thanks for the help so far.

I reversed the wires on the OPSU. Now I get 0 with the key on and 5+ when it starts. I am leaving it this way and I will order a new sending unit. Sounds like that is the problem. The car runs absolutely perfect so I see no reason why it would have crazy high pressure unless the sending unit is not working properly.

I also grounded both leads to the block. I got a 0 reading with the key on and a 0 reading with the car running. I tired the blue/white wire on both terminals alone and I got the same results, one terminal (the one where it is now) is zero with the key on and 5+ with the car running, and the other terminal was +5 with the key on and the car not running.

Now I wonder who reversed the wires??? Does this sound like the real problem? Reversed wires and a bad Oil Pressure Sending Unit? The Porsche dealer worked on it once to do my belts and all the front end seals and a year before that I had a shop do my power steering pump. I know it worked after the pump. I doubt the Porsche dealer would have to remove these wires???? Would they have?

Thanks again for the help guys. I will order the unit next week as I have a few other things I would like to get all in one shipment. I will let you know if it was a bad unit. I have my fingers crossed!
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John
'87 944 N/A (first Porsche)
'95 E-350 Diesel
'03 S-Type Jag 3.0
'03 Taurus SES
'06 Eddie Bauer Explorer

RIP SoCal
Old 08-05-2009, 02:29 PM
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Old 08-05-2009, 02:29 PM
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