Oil pressure gauge issue

[detmatt]

trying to figure out why the gauge in my Challenger won't register where I think it should.
Details....
Freshly rebuilt 383 with about 50lbs of pressure on a mechanical gauge.
I converted to a rallye cluster with a known working gauge.
I was hoping to be able to lose the mechanical gauge that is currently zip tied to the e-brake pedal but with a new Standard sending unit the needle barely moves on the gauge.
The engine is grounded and I use no teflon tape on the threads and even took it a step further and ran a jumper wire from the sending unit body to ground.
I then took the sending from the Imp because it works great and it made no difference.
Today I installed yet another good sending unit with a different value and it registered even lower.
I was thinking maybe something was in the oil galley like an old piece of teflon tape that I used in the past that might be partially blocking the port in the unit when running so I plumbed a line from a fitting into a clear bottle and cranked in order to flush out anything in the galley. After which I drained the oil, changed the filter and refilled with oil that I strained through cone filters twice. I did find some stuff in my double filtering process, small soft stuff, nothing alarming but still no changes. Is it just the calibration of the gauge itself?

This is as high as I can get it to register.

 

[66Newyorker]

What is the ohm range of the gauge? If you don't have the info start by grounding the sender wire and see what the gauge reads. Then if you were hook up a variable resistor the the sending unit wire. You can use a headlight switch and DMM to set resistance. Hope this helps.

 

[66Newyorker]

And also are you getting the proper voltage at the sender wire?

 

[detmatt]

When I ground the wire the gauge pegs high.

 

[66Newyorker]

Also try disconnecting the sender wire and turn the ignition to the on position the gauge should do the opposite of having the wire grounded.

 

[66Newyorker]

Let me know what it does when you have it disconnected and not grounded.

 

[66Newyorker]

What I would do is try a GM sending unit early 70s. Might be the easiest thing.

 

[Big_John]

The FSM has you check the gauge with their tool, but you know those aren't available anymore.

Checking it to ground lets you know if it works at all, and that's a good place to start.

The FSM procedure can be duplicated with a few resistors though. With a 10 ohm resistor in series to ground, your gauge should read high. 23 ohms get you in the middle and 74 ohms should show low.

I would also check the sender. With the engine off, I would figure it should be about 75 ohms, maybe more and guesstimating, I would say with the engine running, and good oil pressure, you'd probably have 20 ohms resistance.

I think someone here made up something to check the gauges. I'll see if I can find it.

 

[Big_John]

Found it!

c-3826 tester for gauges and sensors

Simple to make and would be easier than trying to get the resistors.

 

[detmatt]

Key off resistance of the sending unit is like half an ohm, engine running it pulses with a high of half an ohm.

 

[Big_John]

Just for laughs, see what the resistance of the other senders measure with no pressure on them. You don't have to put them in the car.

 

[66Newyorker]

If it were higher than 1/2 an ohm with the engine running the gauge would be pegged. The pulsing is normal.

 

[detmatt]

The other 2 I have here measure about the same.

 

[detmatt]

So I need one with a higher resistance to get my gauge to read in the normal range?

 

[Big_John]

So I need one with a higher resistance to get my gauge to read in the normal range?

Something is really wrong here.... Are you sure you are reading the meter correctly? Everything hooked up right?

 

[66Newyorker]

From what your readings are your gauge would be on the high side. 1/2 ohm is like grounding the sending wire to the block, would peg your dash gauge.

 

[FinFury]

You need one with lower resistance

 

[detmatt]

It's a simple analog meter and I zeroed it out. Lower resistance than half an ohm?

 

[Big_John]

Higher resistance.

 

[Big_John]

Not to complicate things, but I think something is bad with your meter.

The old analog stuff is great... but it sometimes doesn't age well. Is it at zero when you put the 2 probes together? At full scale when apart?