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post #1 of 9 (permalink) Old 06-13-2019, 03:00 AM Thread Starter
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Oil pressure reading

Hi I have a restored 1750 gtv.When I turn the ignition on the oil pressure gauge shoots up to its highest possible reading and remain there,this is before and after the engine is fired.I have bought new senders with no luck,if I short the sender wire the gauge drops to 0.I've multi metered the sender wire and it is ok,the tachometer and gauge appears to be in good order and the gauge originally worked when the engine was rebuilt.
Any suggestions ?
Cheers Joe
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post #2 of 9 (permalink) Old 06-13-2019, 06:49 AM
Richard Jemison
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Gauge

With the ignition on and you ground the sending wire then the gauge
should jump to highest level. Not "0".
Sounds like wires to gauge are reversed (pos & neg)
Tach is cable driven so it should work regardless of wiring...

Richard Jemison
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post #3 of 9 (permalink) Old 06-13-2019, 07:22 AM
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There are different sending units for old/new, Jaeger/Veglia brand gauges. Did you ever try your original sending unit (that used to work) after the rebuild, or did you install a different sender with the rebuild?

Jay Mackro
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'65 Guilia Sprint GT
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post #4 of 9 (permalink) Old 06-13-2019, 12:23 PM
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Quote:
Originally Posted by Redback View Post
Hi I have a restored 1750 gtv.When I turn the ignition on the oil pressure gauge shoots up to its highest possible reading and remain there,this is before and after the engine is fired.I have bought new senders with no luck,if I short the sender wire the gauge drops to 0.I've multi metered the sender wire and it is ok,the tachometer and gauge appears to be in good order and the gauge originally worked when the engine was rebuilt.
Any suggestions ?
Cheers Joe
You make no mention if this is a new issue or if it's been this since the restoration. The problem could be something as simple as a bad or no ground at the gauge.

Ken
'73 GTV
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post #5 of 9 (permalink) Old 06-13-2019, 01:09 PM
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Originally Posted by Alfajay View Post
No, I don't think it's that; if the gauge weren't grounded, the needle wouldn't move when the signal wire was connected to ground.
Jay, I thought the exact same thing when the temp gauge on my '73 BMW suddenly pegged and stayed topped out when I turned the ignition on. Pulling the wire at the sender would cause the gauge needle to zero out. Thinking it was the sender, I installed a new one and it didn't solve the problem. Pulling the gauge cluster revealed a loose ground connection to the gauge. Reconnecting it solved the problem. The symptoms here sound all too familiar. Respectfully, Ken

Ken
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post #6 of 9 (permalink) Old 06-13-2019, 01:59 PM
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Quote:
Originally Posted by bellagt View Post
Jay, I thought the exact same thing when the temp gauge on my '73 BMW suddenly pegged and stayed topped out when I turned the ignition on. Pulling the wire at the sender would cause the gauge needle to zero out. Thinking it was the sender, I installed a new one and it didn't solve the problem. Pulling the gauge cluster revealed a loose ground connection to the gauge. Reconnecting it solved the problem. The symptoms here sound all too familiar. Respectfully, Ken
Oh, I see your point - the gauge could be getting its only ground through the sending unit and that causes the needle to peg. OK, Redback should add this to the list of possible causes. Previous post deleted.

A simple check for an ungrounded gauge would be to see if the illuminating bulbs for the tachometer & pressure gauge light up when the headlights are on:

- If the lights don't come on, the odds are good that the gauge housing is ungrounded. And if the needle on the pressure gauge moves a bit as the lights are turned on/off, that's a strong indicator that the only path to ground is through the oil pressure sending unit.

- If the lights do come on, the ground for the pressure gauge may still have somehow gotten detached from the tach housing, but that's unlikely.

Jay Mackro
San Juan Capistrano, CA

'63 Guilia spider
'65 Guilia Sprint GT
'67 Duetto
'91 164L

Last edited by Alfajay; 06-13-2019 at 04:00 PM.
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post #7 of 9 (permalink) Old 06-13-2019, 06:50 PM
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Quote:
There are different sending units for old/new, Jaeger/Veglia brand gauges.
That is correct and they work in opposite directions. With one type lower resistance = higher pressure and the other is lower resistance = lower pressure.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #8 of 9 (permalink) Old 06-14-2019, 03:53 PM Thread Starter
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Thanks guys for all the suggestions I think I have tried all with no luck.
It's been fun doubling myself over under the dash.I have pulled the tacho out and all the dash lights work and the unit is properly grounded.
The gauge was working after the resto.and the reason I replaced the sender was due to an oil leak from the unit.I think I will buy another sender and hope that solves the problem -unless some one knows how to check the sender once it is out of the car?
Again thanks Joe
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post #9 of 9 (permalink) Old 06-14-2019, 04:26 PM
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If you measure the resistance between the connector and ground it should vary with pressure. The resistance varies with different type sensors but it most likely will be between 20 and 200 ohms.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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