Oil Pressure Gauge

[The Rocknrod]

I had a 73-87 oil pressure gauge install done on my gauge panel and dont get any pressure readings.
Some background:
I have a known grounds bus bar I'm taking ground readings from.
I have grounds at the gauge panel, ground continuity to the sender (PS154), engine block and gauge ground lead itself.
I have 12V power to the gauge with power on.
I have continuity from the gauge end sender wire to the sender (engine) end.
I grounded the sender wire from the sender (engine end) the gauge went from zero to 1/4.
Unplugged it the gauge went to zero (the bottom/left).
Here is a pic of the back of my gauge. Could the sender wire and power wire be crossed? I did't want to move them yet as I was afraid to damage the gauge.

[ray_mcavoy]

Originally Posted by The Rocknrod

Here is a pic of the back of my gauge. Could the sender wire and power wire be crossed? I did't want to move them yet as I was afraid to damage the gauge.

Yes, it does look like the sender & power wires are reversed. As viewed from the back of the gauge, the sender terminal is on the left, power terminal on the right, and ground at the bottom center.

[The Rocknrod]

Originally Posted by ray_mcavoy

Yes, it does look like the sender & power wires are reversed. As viewed from the back of the gauge, the sender terminal is on the left, power terminal on the right, and ground at the bottom center.

Okay thank you, I will switch them and see what gives.

[The Rocknrod]

I swapped the leads, grounded the sender wire on the engine end and the gauge needle took a dive past the low side out of sight. That is a good thing I think.
Unplugging the sender - Gauge goes to the bottom of the sweep = 0. Should go to the top.
Since I verified 12V again and grounds again...
I can test DC volts between ignition and ground terminals with the ignition on next. Not sure what I'm looking for but I will let you know.

Then ohms between ignition and ground with the sender plugged in and the engine running, but that will have to wait a couple of days to put the other items on the truck together I've been working on (fuel and coolant).

[The Rocknrod]

Originally Posted by The Rocknrod

I swapped the leads, grounded the sender wire on the engine end and the gauge needle took a dive past the low side out of sight. That is a good thing I think.
Unplugging the sender - Gauge goes to the bottom of the sweep = 0. Should go to the top.
Since I verified 12V again and grounds again...
I can test DC volts between ignition and ground terminals with the ignition on next. Not sure what I'm looking for but I will let you know.

Then ohms between ignition and ground with the sender plugged in and the engine running, but that will have to wait a couple of days to put the other items on the truck together I've been working on (fuel and coolant).

I tested the volts between the two sender and 12V terminals on the back of the gauge with the ignition on = 12V
Ohms between the two with ign on = 0 (not to be confused with OL)
12V to ground = 12V
Next will be - ohms between ignition and ground with the sender plugged in and the engine running.

[hatzie]

As Ray said.
Your sender wire should be on the open stud in the picture.
The power wire should be on the stud where your picture is showing your sender wire.
The ground should stay right where it is.
ANNND the top stud should be empty.

[The Rocknrod]

Thanks for the info. That open stud, under the nut is an L-shape bracket/connector.
I switched them. I'll get a pic and post it for posterity.
Any info on the readings i took so far, good or bad?

[The Rocknrod]

Okay 3 pics, one without any wires attached, one above the wires one below. Hopefully tomorrow this bad boy should be working.

[hatzie]

The oil pressure sensor should be 0-90Ω. The 0-60 & 0-80psi senders use the same range of 0-90Ω.
IIRC the oil pressure sender wire dead shorted to ground or 0Ω should be 0psi. Sender unplugged should nail the gauge off the top just like the fuel gauge.
I need to look at my gauge plots to be sure.

If your ceramic calibration resistor is not making good contact with the studs you'll get erratic operation.

[The Rocknrod]

Originally Posted by hatzie

The oil pressure sensor should be 0-90Ω
IIRC the oil pressure sender wire dead shorted to ground should be 0. Sender unplugged should nail the gauge off the top just like the fuel gauge.
I need to look at my gauge plots to be sure.

On mine grounding the sender wire on the engine end the gauge needle took a dive past the low side out of sight. That is a good thing I think.
Unplugging the sender - Gauge goes to the bottom of the sweep = 0.

[ray_mcavoy]

Originally Posted by hatzie

The oil pressure sensor should be 0-90Ω. The 0-60 & 0-80psi senders use the same range of 0-90Ω.
IIRC the oil pressure sender wire dead shorted to ground or 0Ω should be 0psi. Sender unplugged should nail the gauge off the top just like the fuel gauge.
I need to look at my gauge plots to be sure.

If your ceramic calibration resistor is not making good contact with the studs you'll get erratic operation.

I agree, it should operate just like you described ... same as the fuel gauge.

Originally Posted by The Rocknrod

On mine grounding the sender wire on the engine end the gauge needle took a dive past the low side out of sight. That is a good thing I think.
Unplugging the sender - Gauge goes to the bottom of the sweep = 0.

That sounds like you might have an issue with the calibration resistor not making good contact like hatzie described. Or a bad (open circuit) resistor. Either one of those would cause a higher than normal amount of current to flow through the meter movement coil that deflects the needle toward the low end of the scale. And that sounds like what you're describing with the needle going "below zero" with the sender wire grounded.

[The Rocknrod]

Thank you for that info. I can remove the gauge. Doesn't look too tough to remove the little nuts and clean the contacts and resistor.
Can the resistor be tested while I'm at it? Before I put it back together I mean?
Heck I can probably do it (clean it up) installed. What am I looking for test wise for the resistor if I remove it?
Or should I just buy a new one?

[ray_mcavoy]

Originally Posted by The Rocknrod

Can the resistor be tested while I'm at it? Before I put it back together I mean?

Yes, you can use a multimeter (on the resistance scale) to test the resistor. If I remember correctly, it should be in the neighborhood of around 85 to 90Ω. An open circuit reading would indicate a bad resistor.

Originally Posted by The Rocknrod

Heck I can probably do it installed. What am I looking for test wise?

Yes, I suppose it could be measured with it still installed. You'll want to at least unplug the power & sender wires so the reading isn't influenced by the rest of the circuit. And be aware that the calibration resistor is connected in parallel with one of the meter movement's internal coils. So if the resistor is good and making good contact, the resistance you read on the meter will be of the two in parallel. I think the coil resistance is pretty close to that of the resistor so the two in parallel will be about half.

[The Rocknrod]

Okay so remove the leads, set the multi-meter (in my case a digital fluke) to resistance (ohms) and check the readings across the two points/connections. Right?
I'm all over this.

[The Rocknrod]

I can choose either MIN or MAX on my Ohm dial.
On Max I get 00.0 reading and on Min I get "OL"...

[The Rocknrod]

So I removed the nuts and L-Shaped connectors cleaned it up with alcohol and took readings with my Fluke and it read across 81.4/5. That's without the connectors attached.
What does that mean?

[The Rocknrod]

And now I put it back together after thouroly cleaning the connectors and such. Funny thing, when I plugged the sender wire into the sender and turned on the key the gauge took a dive left into the low side past where you can't see the needle.
Unplugging the sender wire at the gauge or at the sender either one it only goes up to before the first line at the left of the gauge.

[ray_mcavoy]

Originally Posted by The Rocknrod

So I removed the nuts and L-Shaped connectors cleaned it up with alcohol and took readings with my Fluke and it read across 81.4/5. That's without the connectors attached.
What does that mean?

Was that measuring across the meter studs with the nuts, connectors, & resistor removed? Or was that measuring the resistor itself?

81.4/5Ω is within the range I'd expect for either one so whichever one you were measuring sounds like it's okay.

Originally Posted by The Rocknrod

And now I put it back together after thouroly cleaning the connectors and such. Funny thing, when I plugged the sender wire into the sender and turned on the key the gauge took a dive left into the low side past where you can't see the needle.
Unplugging the sender wire at the gauge or at the sender either one it only goes up to before the first line at the left of the gauge.

Hmmm? The overall behavior of the needle swinging to the left with the sender plugged in & key on and moving to the right with the sender unplugged sounds normal. But the needle positions seem out of range.

Do you know if the procedure of retrofitting that gauge into your cluster involved removing and re-installing the needle? If so, there is a possibility that the needle was not clocked correctly when it was put back in place. It's simply a small round shaft with nothing to "key" the needle to a particular location in relation to the meter movement internals.

[The Rocknrod]

Originally Posted by ray_mcavoy

Was that measuring across the meter studs with the nuts, connectors, & resistor removed? Or was that measuring the resistor itself?

81.4/5Ω is within the range I'd expect for either one so whichever one you were measuring sounds like it's okay.

That was with the resistor on the back of the gauge still on it, no nuts or connectors. From one stud to the other. I couldn't figure out how to remove it (the resistor) as it didnt come out easily and I figured I would crack it if I tried to pry on it.

Hmmm? The overall behavior of the needle swinging to the left with the sender plugged in & key on and moving to the right with the sender unplugged sounds normal. But the needle positions seem out of range.

Do you know if the procedure of retrofitting that gauge into your cluster involved removing and re-installing the needle? If so, there is a possibility that the needle was not clocked correctly when it was put back in place. It's simply a small round shaft with nothing to "key" the needle to a particular location in relation to the meter movement internals.

No I don't know, I'd have to ask a member here who did it for me.
So I also ran test leads instead of using the installed wires for the sender and 12V and ground. No changes.
I could run to Orielly and try a new gauge sender...
On the gauge if I removed it and adjusted the pointer... Hmmm, I'd have to know where to put it.

[ray_mcavoy]

Originally Posted by The Rocknrod

That was with the resistor on the back of the gauge still on it, no nuts or connectors. From one stud to the other. I couldn't figure out how to remove it (the resistor) as it didnt come out easily and I figured I would crack it if I tried to pry on it.

Okay, the removal of the nuts electrically disconnects the resistor from the gauge. So in that situation you were measuring the resistance of one of the coils inside the gauge.

The resistor normally just lifts off after the nuts are removed, but I think you made the right choice of not prying on it with it being stuck.

Now that you have things cleaned & re-assembled, try taking another resistance measurement between the two studs (with the wires unplugged). If your resistor is good and making good electrical contact, you should now get a reading in the 40-someΩ range (resistance of the meter coil 81.4/5Ω in parallel with the resistor that should also be in the 80-someΩ range). Rtotal = 1 / ((1/R1) + (1/R2)) where R1 and R2 are the meter coil & calibration resistor.

But if you still get that same 81.4/5Ω reading, that would indicate a problem with the resistor (bad or still not making good contact).

[The Rocknrod]

Thanks Ray. I went out and took readings from one connector to the other with no wires attached. 41.4 on the Fluke. Your good.
So what do I do now?

[ray_mcavoy]

Originally Posted by The Rocknrod

Thanks Ray. I went out and took readings from one connector to the other with no wires attached. 41.4 on the Fluke. Your good.
So what do I do now?

You're welcome! Looks like your gauge & resistor check out okay.

There is one other coil inside the gauge movement that you can measure (again with the wires disconnected and meter set to resistance). This time, check between the ground terminal and sender terminal. I think that should be somewhere close to 100Ω if I remember correctly. Pretty rare for there to be a problem with the gauge's internal coils, but worth checking just to be thorough.

If that checks out okay, the positioning / clocking of the needle being off is the only other thing I can think of that would explain the needle going down below zero.

[The Rocknrod]

Yep it read 98.8Ω

[The Rocknrod]

So if i remove the gauge then on post 17 "I plugged the sender wire into the sender and turned on the key the gauge took a dive left into the low side past where you can't see the needle."
So do that without a pointer and place the pointer on the shaft at the low point of the gauge.
Or the opposite, when I unplug the sender wire place the pointer at the high level. That might work?
Of course power and grounding and all...

[The Rocknrod]

I did it. First pic with sender wire Not grounded. Second pic with sender wire grounded. Thoughts?