almost done - details

[cmcfaul]

So engine is in. New crank, pistons, bearings, the works. Runs great. Just Solved a charging issue so now its making volts and not running off the battery.

I replaced the Voltage Regulator which mounts to the rear fuse panel. Right after replacing it the oil pressure gage now is pegged all the time. If I disconnect it, it's still pegged.

Is this the sign of a bad pressure sensor or another electrical problem?

When disconnected should it read zero or go fully to the top?

Thanks,

Chris

[AlfonsoR]

I am not expert on things electrical, but I would expect that if disconnected, it should go to zero. It sounds like your gage is stuck.

[timmy2]

Pegged with power on or all the time?
Disconnected the regulator, the pressure switch connection or the gauge?

To test the sender:
With power on and the pressure sender wire disconnected the gauge should go to max, grounding the wire to a metal part of the engine should send the gauge to zero.
If the sender is faulty it shows open just like taking off the wire.
My sender measures 15.4 ohms to ground with the wire disconnected. Yours may read open or infinite ohms which would peg the gauge.

[cmcfaul]

great info.

With power off it reads zero. With power on it pegs. With power on and wire disconnected it is pegged. I will see what happens if I ground it.

What type of sender does my car take?

73 911 E
2.4 L
MFI

Are the $25 after market versions OK?

[cmcfaul]

OK, crap

Grounded the wire that goes to the pressure sender and it stays pegged. I jiggled all the wires. unplugged and plugged everything back in. put the old voltage regulator in and still the same.

uggg

[timmy2]

Ok, time to see if the sender wire is toast. Connect an ohmmeter to the wire end at the sender and then pull your gauge and check for continuity to the input wire on the gauge. Another test for the gauge function is to apply a grounded jumper to the gauge input terminal and turn the key on. ( same test as at the sender)
Did you measure the resistance at the sender to ground?

[docrodg]

Originally Posted by timmy2

Ok, time to see if the sender wire is toast. Connect an ohmmeter to the wire end at the sender and then pull your gauge and check for continuity to the input wire on the gauge. Another test for the gauge function is to apply a grounded jumper to the gauge input terminal and turn the key on. ( same test as at the sender)
Did you measure the resistance at the sender to ground?

Nicely put... easy way to test without a bunch of messing around or special crap.

[cmcfaul]

Fixed,

Had to run a new wire from the sender to the gage.

Chris

73 911 E

[timmy2]

Originally Posted by docrodg

Nicely put... easy way to test without a bunch of messing around or special crap.

Being an electrician for 30 years troubleshooting 500,000 volt circuit breakers makes a guy keep it simple!

Glad you found the problem Chris, need a picture to go with this thread!

[Walt Fricke]

Alfonso

The oil pressure gauge on our cars pegs if the sender is disconnected. The sender is basically a rheostat, with fingers moving over a wound coil. More pressure, more resistance as the current flows through more coil windings on its way to the ground. An open in the wiring, like a break in the resistor wire from wear and tear, gives infinite resistance.

The gauge is built so that current is pulled through the parts which make the needle move, but some of that is diverted through the sender, most when no pressure, less as the pressure rises. I think the virtue of gauges of this sort is that gauge movement mirrors the resistance change and is unaffected by voltage variations or fluctuations.

The most common issue, other than a failed sender, is the wire coming off the sender. Having a break along the wiring line from the sender via the 14 pin plug up to the gauge in the dash is less common, I think. But wherever the break is, it pegs the needle.

[Walt Fricke]

Oh - the oil tank level sender behaves the same way as the oil pressure sender. I think the oil temperature sender does as well, but for some reason I've never had one of those fail or the wire come off its terminal. The temperarture sender doesn't have any moving parts.