Oil Pressure Gauge Issue

[James Grant]

Folks:

I have an interesting problem, I have had a sudden drop in oil pressure reading from the 40ish range to 20lbs. First it was the upper station and then the lower station about a week later.

I replaced the sender with the correct dual meter unit and still have the same readings.

The mechanic I'm using suggests replacing both the upper and lower gauges and see what they show. Figures they are both bad.

We put a gauge directly to the sending unit and it reads in the 40 lb range so it's making pressure.

I have checked and re-checked wiring - cleaned all connections and tightened.

In other thing is an annoying one second tick electrical pulse coming from the tachometer hour meter, pulses the needles on the oil pressure, I don't recall seeing this before.

Anyone seen this? I would assume the hour meter should run smooth.

Just a little irritating.

thanks

[Panhdjoe]

This is almost with out a doubt a ground problem. When a circuit does a feedback such as you describe it is trying to find a ground through another circuit. This is a little hard to explain with out doing a mini class on DC electricity. The oil pressure circuit has battery voltage at the gauge and the sensor (also called a sending unit) usually provides a variable ground to the gauge. Chances are that another circuit possibly the hour meter has a pour ground. causing faulty readings on the oil pressure gauge. Voltage drop testing on the ground side is the best place to start.

[psneeld]

The one second tick is normal as far as I know...many hour meters that I have run tick...and pulse into one or other gauges. Whether the slight tick into the other gauges is OK, I'm not sure but plenty of people I know run them that way with no issues that I've ever heard.

[James Grant]

I understand the ground fault as you describe, I've cleaned and tightened everything I could find.

Everything is tied together so I guess it's simply a matter of time before I find the bad ground connection.

Seemed a little too strange that both gauges would fail at the same time and that they both read the same pressure pretty much half of what the actual oil pressure is.

Thanks for the help greatly appreciated

Starting loop- 8 months 1 day - not that I'm counting

[meridian]

use a piece of wire connected to a known good ground point and use it to check the ground output of each gauge. that should narrow it down.

[jleonard]

I second using an auxillary ground to pinpoint the issue. And i highly doubt both gages would go bad at the same time.
My hour meter/ tach does not tick.

[James Grant]

Problem solved- traced back every wire for bad insulation bilge to fly bridge nothing, I cleaned every connection I could find to no avail - replaced the sending unit - no change - gauges showed 10 lbs. pressure on start-up - tested oil pressure at the block - 50lbs +/- 5% confirmed good pressure - replaced both oil gauges..............both reading exactly the same at the engine block - 50lbs +/- 5% .... I'm a happy camper