oil pressure gauges

[jim wick]

450 diamonds from 1995. Twins (all 4 gauges, fly-bridge and pilothouse) oil pressure gauges read low. I verified with a set of mechanical gauges right on the engine. if i have 25 psi they read 6 psi. I replaced sending units and made sure they were marked “D” for dual stations. Replaced the gauges, no help. The problem is that they set off my stock cummins alarms behind the tachs at idle, and also dont give me a true reading underway. Sounds like maybe too long of a run for the undersized wire that cummins supplied in the 90’s? Any thoughts? Any easier way than to run 2 new 30 foot wire harnesses?

Topic

[Tony Athens]

Early Cummins off engine harnessing used 14Ga wire for the Ground, the Red + up the the dash, and the purple IGN + back to the engine——————————-Major voltage drops..

All these of those were upgraded to 10Ga down the road..

Running a new direct ground to the panel was a good call.

[jim wick]

Got it

Im 99 percent sure I got it. Wiring is a fickle bitch. bitch. I ran a new ground from the panel to the gauges. I hope that’s kosher. I guess the 30 foot run back to the engine through the harness was not doing it for me. No more low oil alarms. Volt meter reads 13.5 now instead of 11.5. Thanks everyone!

[Tony Athens]

Yes, we did modify the our PCB board and moved 2 alarm set points..

Coolant temp moved lower to about 198-202F from 205F +/- 3 degrees ( way safer)

Low oil PSI set point to about 6-8 PSI from 10 -12 PSI to solve the nuisance alarms at low idle when hot

VDO gauge curves are on the web site (OHM’s vs. read-out specs) .. “D” is a dual station sender with a 50% different OHM scale.

[jim wick]

I installed good quality mechanical gauges after the cheap ones took a shit. 700 rpm the mechanicals say 25-30. Pilot house and fly both read 5.

I took a new gauge and hooked it to the VDO “D” sender and the battery right next to the sender. All new wire/crimps/gauge/sender. Reads 5.

Granted it’s a single gauge on a “D” sender. 5 was not what I was expecting.

Two of my 4 boards I got from you. I believe you changed the alarm so there was not so many false alarms.

[Tony Athens]

Jim,

Let’s look at the whole “enchilada”……..

1) What is your true OP at idle, hot, measured with a decent 0-100 PSI gauge?

2) What does your instrument read vs. “real”

3) Cummins alarm boards are notorious for setting off an alarm even when “real” OP” is within specs..

4) who sorted it out —“ME” , about 3-4 years ago when I got tired of answering emails about the issue when there was never a
“real issue”..Just a poor calibration in the circuitry of the alarm board……

Come back..

[jim wick]

corey, in another thread concerning low oil pressure you said…..

“You can place a 10-15 ohm resistor in-line on one of the sending unit wires to bump up the PSI value… the problem is that the Cummins spec is down to 5-6 PSI at idle but the alarm indicates at 8-10 PSI… hmmmm Who thought of that one?????”

Is this an option if it is my long wire run? 10-15 ohm? how many watt resister?

[jim wick]

clark, thanks. I will do it! Definitely a smart try before I buy and install another harness. thanks buddy

[jim wick]

Corey, thanks as usual. I will take a better look/clean at the terminals and also take a picture. I did not notice any corrosion and since the problem is both sides and since this seems to have been a problem since new I did not give corrosion much of a thought. I do want to do a quick short run check just to narrow it down. Happy holidays

[Clark Leighs]

Take a good hard look at the connections/crimp terminals. I have fixed a bunch of poorly reading guages by simply reterminating them. Hopefully there is some slack in the wiring so you can cut off the old terminals and crimp new ones on. Otherwise you may need to install new wire.

If the bared wire looks a bit discoloured or oxidized lightly then the use of some ROSIN PASTE FLUX, just the paste put on the wire and then heated will take off most of the oxides. Electronics supply shops.

Afterwards, Just dip/wipe with some alcohol and then crimp on a new terminal. Take a look at the mounting pads for the ring terminals or the blades for the flat blade/socket terminals and clean them up . THen use a spray to protect them and the wire strands.

NO ACID CORE SOLDER and NO ACID FLUX.

[Corey Schmidt]

Jim, while assessing the wiring, you didn’t notice any loose or corroded sections of wiring?

What AWG size do you think the wires appear to be in the EXT harnessing?

Have you tried the new gauges with an ad-hoc short run of wiring just to test?

Got any pictures of the gauge panels you currently have?

[Author]

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