Electric Oil Pressure Gauge Problem

CandBMotorworks

CandBMotorworks

C&BMotorworks
So this is actually a problem with a 124, but I figured I would ask because I imagine one of you has encountered this before.

Key on, engine off, oil pressure gauge goes max.

Key on, engine on, gauge drops to zero.

At one point the wires to the ignition switch were disconnected. I have them connected per the wiring diagram, and it seems like the connections are fairly simple...some provide power in key on and others only when turned to start.

Thoughts? My initial impression is that the gauge is wired backwards, though I don't know how unless someone pulled it out of the dash and then screwed up when reconnecting.
 
Gauge goes to max sweep with key on (not running) - normal operation, means gauge (power, ground) wiring is OK, I believe. That's what I see on mine (124 OP gauge)

IMG-20200219-112004.jpg


IMO, chances are the sender is bad. Try grounding the wire with the engine running, if the gauge goes full pressure, then the sneder is definitely not functional. Can try fiddling with the connection at the sender to see if it comes live first...
 
CandBMotorworks said:
So this is actually a problem with a 124, but I figured I would ask because I imagine one of you has encountered this before.

Key on, engine off, oil pressure gauge goes max.

Key on, engine on, gauge drops to zero.

At one point the wires to the ignition switch were disconnected. I have them connected per the wiring diagram, and it seems like the connections are fairly simple...some provide power in key on and others only when turned to start.

Thoughts? My initial impression is that the gauge is wired backwards, though I don't know how unless someone pulled it out of the dash and then screwed up when reconnecting.
Click to expand...

It sounds like your gauge is hooked up to a sending unit for an oil pressure light. When you have no oil pressure the sender is grounded, light goes on; when you start the engine oil pressure breaks the ground and the light goes off. When hooked to a gauge it does exactly what you are seeing.
 
My recollection on mine was that it read zero with the engine not running. When running it would be at whatever pressure indication related to rpm and oil temperature. Mine would not sweep, it is too old for that.

I don't know how the Honda engine set up works but OE on a Fiat it wouldn't do the sweep.
 
Hussein, FWIW, that gauge cluster would look great with a Carbon Fiber or matte black background. (IMO)
Symmetry of the gauges and lights look great.
 
My oil pressure gauge behaves like Karl explained above. You might take a look at the sending unit. The factory ones that I have seen tend to be much larger than the idiot light sender. He is a photo of the two connected to a port doubler (my 1500 block was not drilled for the oil pressure sender):

MWB Banjo Port Doubler with Oil Warning & Pressure Senders.jpg


The oil pressure sender is the silver one on the right with a connector on a pigtail. The idiot light sender has a blade connector on the end that is hidden by the right angle boot.
 
bbrown said:
Hussein, FWIW, that gauge cluster would look great with a Carbon Fiber or matte black background. (IMO)
Symmetry of the gauges and lights look great.
Click to expand...

Thanks Bob. I was going to cover it in black vinyl to match the other gauge cluster, but I think I like the contrast, since the gauges are black-rimmed. I don't feel that the CF look will go with the rest of the interior..
 
Strange, I've had over a dozen Fiats and Lancias with the oil pressure gauge and none went to max with the key on-engine not running. They behave like the water temp and fuel gauge.


lookforjoe said:
Gauge goes to max sweep with key on (not running) - normal operation, means gauge (power, ground) wiring is OK, I believe. That's what I see on mine (124 OP gauge)
Click to expand...
 
Mark said:
Strange, I've had over a dozen Fiats and Lancias with the oil pressure gauge and none went to max with the key on-engine not running. They behave like the water temp and fuel gauge.
Click to expand...

Must be because I use VDO senders, so it registers in reverse.
 
CandBMotorworks said:
Key on, engine off, oil pressure gauge goes max.

Thoughts? My initial impression is that the gauge is wired backwards, though I don't know how unless someone pulled it out of the dash and then screwed up when reconnecting.
Click to expand...

With the key on/engine off, the red "idiot light" (@ lower left, next to the 0psi hashmark) should be lit, with the gauge needle reading 0psi.

With the key on/engine on, the red "idiot light" should be off (assuming you have oil pressure), with the gauge needle now reading whatever oil pressure the engine has.

It sounds like you may have 2 wires hooked up incorrectly, either at the gauge or on the engine. Those 2 wires would connect to the oil pressure sensor (aka "idiot light") & the oil pressure sending unit (controls the gauge needle).
 
gene cooley said:
Does this mean that when your gauge reads 80psi that you really have about 20psi?
Does the pressure go up at idle?
Click to expand...

I made a new facia that reads in reverse, for the stock X1/9 gauge.

X19-0281.jpg


For the 124 gauge I ordered the correct sender from MWB. Right now, the reading is reversed, so high pressure reads low, low pressure reads high. Idling, since the idle is way too high, shows around 30ish psi - zoom in on gauge, it's showing above 40, so it's actually below 40

IMG-20200219-153745.jpg
 
To get back to the original question, a 124 with oil pressure gauge will have two sending units on the oil filter bracket. The small one is for the light and the "can" is for the gauge. I have seen spiders where the oil gauge was added (later years did not have an oil pressure gauge) and just used the same sending unit which won't work right.
 
carl said:
To get back to the original question, a 124 with oil pressure gauge will have two sending units on the oil filter bracket. The small one is for the light and the "can" is for the gauge. I have seen spiders where the oil gauge was added (later years did not have an oil pressure gauge) and just used the same sending unit which won't work right.
Click to expand...

Thanks, and thanks to Jeff Stich for his explanation, which makes total sense - I didn't think to look for an idiot light. I can say in the short distance I have driven this vehicle no idiot lights came on.

The oil pressure gauge appears stock and certainly has been in the car longer than we have owned it. The problem is that I haven't really had this car in my possession for some time and so I don't even know (recall) whether the gauge ever worked correctly. It is possible that my buddy JB did some engine bay work and accidentally swapped the wires. I have to believe it worked correctly at one point.

I will have to hunt for the wiring diagram. I assume that short term I can simply swap the wires on the two switches to see if that corrects the problem? (As in, swapping the wires won't cause component damage?)
 
CandBMotorworks said:
Thanks, and thanks to Jeff Stich for his explanation, which makes total sense - I didn't think to look for an idiot light. I can say in the short distance I have driven this vehicle no idiot lights came on.

The oil pressure gauge appears stock and certainly has been in the car longer than we have owned it. The problem is that I haven't really had this car in my possession for some time and so I don't even know (recall) whether the gauge ever worked correctly. It is possible that my buddy JB did some engine bay work and accidentally swapped the wires. I have to believe it worked correctly at one point.

I will have to hunt for the wiring diagram. I assume that short term I can simply swap the wires on the two switches to see if that corrects the problem? (As in, swapping the wires won't cause component damage?)
Click to expand...

Both wires "should be" grounds. Short each one to the block and watch for the light or the gauge.
Of course you might still have a problem with the gauge, the sending unit for that seems to have it's own set of problems...
 
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