Gauge issues with oil psi

I'm running into some strange issues with oil pressure in the dual helm station. The issue seems to have to do with voltage to the oil gauges however the voltage is not low like 11v when the motors are running its up around 14-15v due to the alt. My other boat has the same situation but the gauges work great. There is also a dual set of gauges connected on the FB they are also wacky.

The symptom is with the key on motor off oil PSI reads anywhere from 5-40psi on the oil gauges and kind of moves around on its own. When I start the motors both go to 20 then back down to 10 then up to 20 but don't really change with the rpm's its like they are in sync.

New gauge, new sender, new wire sending, power and ground setup in the engine room isolated from the panel I get 30-40psi at idle. Before I start running all new sending wires and or power wires I thought Id ask if anyone knows what else might be at play here. My other boat only has one motor. I'm thinking something might be going on with the dual set of gauges or its just one bad wire. Problem is the bad wire could be going to FB ext as they are all in parallel.

Any pointers troubleshooting this one would be appreciated. Do the oil psi gauges on your boats move when you turn the key on without starting the engine? If not what might cause this?

CEC

The oil pressure gauge should move to zero and stay there when the key is turned on without starting.
The oil pressure sensor loop is a simple variable resistance loop. Dual stations use two gauges in parallel so the sensor resistance is either twice or half that of a single depending on manufacturers.
Find the sender and disconnect the wires and measure the sensor resistance. The reading should be steady. If so connect a resistor to the sensor leads of about 100 ohms. The gauges should read somewhere onscale and steady. If so have someone watch the gauges while you gently wiggle the wiring harness from FB to engine.

Thank you High Wire. I assume you are referring to the port side helm and port side fb gauges are in parallel and the starboard pare the same. This is what I find in the wiering to be. What’s odd is the port and starboard helm gauges are acting sporadic in sinc with both keys on, and they are not connected to the same senders but one from each motor. The new sender and gauge I connected separately all new wires jumped to the batter and that works.

I’m assuming there is something in the panel causing static resistance to both of the existing port and stbd oil gauges. It’s tight under there lots of connections. My fear is I need to rip it all apart and rewire if I can’t find the source of resistance. The only common connection between the gauges is the ground so I’ll start there. Each key supply’s power to each side of the gauges. So I have to guess it’s a ground right?

Thanks for your reply

CEC

Both engines wiring should be completely independent even the negatives except for a large negative battery cable between starting batteries. It’s easy to accidentally co-mingle the instruments through things like backlighting and fuel gauges.

Thanks both are independent with the exception of exactly what you pointed out. The pull switch for the gauge lights is wired to both. In the middle of running some new sending wires. Have a feeling the wire is bad and I’m seeing things in the fb that could be causing issues. Strange that one of the fb oil gauges seems to be working ok. I think I’m dealing with old wire issue at this point. I’ll post up if I find a specific cause.

Still fighting this one. Currently I have installed the new dual sender and have one of the new gauges. Mechanical gauge reads 43psi cold. I ran the new gauge to the batter and jumper sending wire and it reads 41 psi.

I believe I nailed it down to the original wire harness sender connections. They are no good and the oil gauge on fb is dead causing additional issues. Running new sender wires and adding corosponding new senders and gauges for oil and temp on both my Lehman 80’s.

This is the first boat Iv had with dual gauges. I’m new to working on this setup excuse my ignorance, but I can’t search up this info for some reason: I’m wondering if someone knows why does the oil gauge read correctly when I have only the one oil pressure gauge connected to the dual sender? I was expecting it to be double the correct psi with only one gauge connected. Is that not the typicaly case? Isnt the dual sender sending out double the resistance to make up for connecting two gauges? I currently have Faria dual 80 psi sender with one Faria 80psi gauge connected. I was told the gauges are not spicific to single or dual setups. If that’s incorrect, and I need special dual gages I’m going to need to return some stuff!

Thanks
CEC

The gauges are not specifically dual, but the sender is. It is comprised of 2 separate circuits giving resistance to the current coming via the gauge.

The dual Faria oil pressure sender I have has one terminal. I suspect it somehow knows when only one gauge is connected to it?

The resistance value of the sender is supposed to be matched to either a dual or single gage setup. My JD engines were installed by Defever with the incorrect temp and oil senders (I have dual helm). PO said that several "$100/hr yacht techs" looked at it over the years but couldn't explain the 100psi oil gage reading......
I couldn't get a good answer from the gage folks regarding correct sender part numbers, so I just installed 2 transfer switches (PH/FB) in the lower helm. All gages read normal values now at either station.

Luke,
Thanks that's why I was expecting the one gauge to read double. I got the part from reputable source and called to confirm they sent the correct sender. I guess I will have to wait until the second gauge arrives and I can install it to see if they both read correctly. I'm close to doing exactly what you did but rather not have to switch. I'm going to try running one sender wire for both gauges first. Once new sending wires are in should be easy right haha. Planning to go to analog to nmea into Ray a98 at some point, but for now I just want working temp and oil gauges up and down. One very strange thing I noticed by accident is if I touch the sending wire from the old gauge to the new senders outside metal housing the old gauge reads correctly right at 40psi (goes up when motor starts) - maybe just a coincidence on the ground resistance...


Thanks
CEC

Running a "test wire" between sender and gage is a good idea and will isolate problems with wiring harness/connectors. My wiring harness has 5 points of connection between the sender and gage......crazy......easy for installers, PITA for the owner years later!
When I was troubleshooting my issue, I took the opportunity to separate, brush, treat each of the plug-in connectors.

I did exactly that but the sender connections are just not good enough to save and I don't want to try and redo. Running pair of 12g good Anchor wire from motor to helm and FB. The grounds on the existing gauges don't go to a ground stand off they go to the bracket post. There is a ground on the gauge but its not connected to any of them. I messed around with a few jumpers I made and I think I'm going to need to change the ground for the new gauges. I have books some of the better ones on boat electrical and there's limited info in them on gauges other then how to test them.


My plan is to just isolate the new gauges on the ignition for both sides. The existing old gauges have zero info on them other than the connection posts. There are two sender connections on the oil psi gauges though - two S S an ING and a N. Unsure why the gauge has two sender connections, but I'm guessing one is for a jump to the second gauge and one works and one does not. Ripping it all out and starting over seems to be the best way to deal in this case. Nothing beats clean labeled correct wiring. All the factory gauge wiring jumpers are cheap connectors with un-tinned 38yo wire. At least the tachs work well

CEC said:

The dual Faria oil pressure sender I have has one terminal. I suspect it somehow knows when only one gauge is connected to it?

Click to expand...

Interesting. I've never seen a one terminal dual sender. I can see how it might get a bit confusing.

If all else fails you can go for a dual terminal sender like this. $35


https://www.fisheriessupply.com/vdo-gauges-dual-station-oil-pressure-senders-for

I looked at the vdo dual kit but I already have the one new sender and gauge. For what it’s worth both old senders on the Lehman’s have one terminal. I was fully expecting double psi with one gauge connected with the new sender and gauge.

I’ll know if two gauges read correctly this weekend and post up progress. It would suck to have to make two separate runs per sender I want to avoid that if I can. Already have a bunch of jumpers made. I plan to test everything direct +- sender to verify before installing.

The PO did a lot of wiring work everything that was done is excellent work. It’s obvious though that no one has touched the gauges since 1979 �� it’s time.

Tonight I found this on Faria site https://fariabeede.com/site_manuals/IS0007E.pdf
At the end of the doc Note c. “ A floating ground sender may be used in a standard ground system but not vice versa.”

I’m fairly sure my exhisting gauges are using a floating ground. None of the neg terminals are connected just the bracket. My best guess is this is the source of my issues as the senders in the boat and the new one are standard ground senders.

I’ll need to switch them all to standard ground. Hopefully I won’t run into ignition issues when I add the standard ground using the power off the ignitions. Anyone know if I’ll run into issues with that? I see floating ground senders have second terminal for grounding to the motor that might be my best option. Eat the $40 sender I got and get the right one.

Edit: looks like a can of worms I’m just going to get the right sender if anyone’s curious it’s this one. Faria, SENDER (Oil Pressure) (1/8\ NPTF American 80 PSI) (Dual Float)", 90514

Thanks
CEC

Well tonight I fixed it! The confusion was caused by someone before me trying to fix the issue when a gauge was broken on the FB. The floating ground I (had) was not stock. Brian at American Diesel was a huge help providing his knowledge about my boat make and OEM gauge setup. He convinced me someone had messed with things - yep he was right...


Someone moved all of the grounds to the gauge bracket posts. My guess is they did this because when grounded to the G on any of the old gauges the gauges would all just peg. Without ground the readings we off but at least they moved.. This is what was causing all of my strange readings in my posts above.


To fix I redid all of the connectors, put in the new oil gauges, and put the grounds in the right spot. I was able to use the factory sending wires and all other factory wires.


I don't fully understand how power was even getting to the old gauges without a ground, but I'm thinking the one bad oil gauge on the FB was shorted internally (probably rain water) and feeding a ground back through the incorrectly connected mounting post, and into the sending wires. The incorrect grounds and broken gauge created all kinds of strange readings into the sending wires.




Thanks for the help.


CEC