New problem. (yay!)

For whatever reason, as soon as I turn the key, before the engine starts, the VDO oil pressure gauge pegs out well past 80psi (probably 120, but 80 is the higest number.)

The idiot light works as expected. Its green while the engine is cranking, but goes out about 1 second after the engine fires.

The sender is the standard VDO dual sender using a paintball hose remote hose, and a study mount to the case.

I have switched the leads at the sender to rule that out.
I cleaned the ground between the sender and the mount.
Not yet cleaned where the mount attaches to the engine case, but the connection there is solid and has lots of contact.

I forget how the sender works. Does it work by grounding itself?

Possible causes:
Bad sender.
Bad gauge.
wire pinched somewhere between the gauge and the sender?
wire pinched between fuse block and gauge?

Missing something?

Spend too much time trouble shooting this, and the car is still idling too high. No more time to work tonight. Sick.

Zach

Just ground the lead and see if it changes. If I remember correctly, they do that if the sender lead is not attached.

Oil pressure is highest when the engine is cold. Mine drops off over the first 10-15 miles as temps go up. If the high pressure doesn't last too long, I'd thin its probably OK.

Oil pressure is highest when the engine is cold. Mine drops off over the first 10-15 miles as temps go up. If the high pressure doesn't last too long, I'd thin its probably OK.

Usually the engine needs to be turning to make pressure. The gauge peg as soon as the key turns, before the engine even cranks.

My engine usually makes 70 to 80 psi pressure on start up. It has never gotten anywhere near pegging the gauge. I am fairly confident that the issue is either the sender, gauge or wire - not the engine.

Zach

Might be the zener diode inside the gauge is kaput.
This basically moves the gauge scale.

If this is the case, it might be that your voltage regulator gave up.
Please check charging voltage when the engine is on.

Wires hooked up to the gauge correctly? Ground, power, sender, light?

--DD

generally, for a VDO electric guage, open signal wire sends the meter to fullscale, grounded sends it to zero. Somewhere in the middle does sound like an internal guage fault.

If you disconnect the signal wire at the guage, you are testing the wire and the guage head. Then disconnect at the guage to test only that.

Wonderful. That will be helpful. Tonight I'll pull the gauge and check continuity of the wire ends. That will tell me if the wire is broken somewhere. If not the wire I need to check the voltage regulator and then replace the gauge.

Reading full on eliminates bad connections between gauge and fuses if I understand correctly.
Zach

no - fullscale is open (no connection).
zero is short to ground

Having the same problem,,,

The sender must be grounded or it will peg the gague needle.

I had the same problem. Turned out to be a bad sender.

On cold mornings, my gauge would occasionally peg with cold oil, due to the sheer pressure. One morning, the gauge was running at 60psi at idle, and then I went off to drive, gauge pegged as it sometimes would, then when I pulled up to a stop sign, the gauge stayed pegged.. took the sender out, and it turned out I broke the sender. It was a very old sender, but it still broke due to being overpressurized I believe.