Gauge help. Multiple questions.
 

To start last year I was battling my oil pressure gauge on my starboard engine. Anything over 3000 rpm and it would drop to 0 and back up. Checked on manual gauge and it never dropped off. Ran that way all year.
Over the off season i pulled both engines. to have the transom assemblies replaced. I replaced all the maintenance items, IE.. starters, plugs, wires, caps, rotors, impellers. and cleaned and painted the engines. also cleaned the connections to the oil pressure senders and tightened the push on fitting. Wishing I cut it off and put on an screw on fitting now. Now running it this year both oil pressures gauges are doing it. Also soon as i hit about 3500 rpm the Tachs start bouncing around as well, boat still runs strong even when the tachs are going nuts. I've checked the grounds behind the dash, all of the engine grounds seem tight. ive messed with the wires going to the oil pressure sender and the oil light sender as well. still no change. I have to be missing something. I went as far as to get two new Livorsi oil pressure gauges, they are updated and plug in style as opposed to the standard Gaffrig gauge connections. none of the wires match up so I haven't installed them yet. Any ideas or places to start would be great.


I forgot to add the fuel gauge. it reads full pretty much until i'm out of fuel then drops. The yellow light comes on and its still showing full.

I suspect ground problems for the issues.

If you painted the engines, the distributors may not be making a good ground.
Try running a ground wire from one of the dist cap screws to a good ground.

The oil pressure sender grounds through the threads going into the engine block. You can't use sealer on it.

I tried the ground wire on the distributor cap trick already with no change. I suspect I need to pull the main harness connectors and clean and spread the pins. I was just seeing if i'm missing something else i'm not aware of.

Have you tried hooking up a Fluke while you're running to see if there is a dramatic voltage drop at that RPM? I am fighting gauge issues this year as well.

Don't forget guys that both of your boats are close to 20 years old. The main ground and positive cables can start to corrode on the inside where you cannot detect it. I went thru similar chit with '97 Sonic. Worth a try. Good luck.

No doubt. I had a no start condition on the old 35. Checked battery good. Turned switch to other battery, engine would fire. Reached down to confirm battery terminals were tight, and the positive cable pulled right out of the crimped eyelet/terminal. Poor crimp from factory - or it loosened up over time. Boat was an '02.

Run a temporary ground directly from the negative battery terminal to the negative of the gauges.
Same with other problem areas. Grounds can be a pain, old wiring, plugs, connections etc.

Had a Formula with similar issues. Replaced the gauges with AutoMeter ProComp Marine series. Problems solved.

I went to Autometer gauges also and I have no complaints other than the fuel Guage still isn't consistent. It's not cheap but it sure makes the dash look sweet. And of course, grounds grounds grounds as already mentioned

Finally getting this boat close to perfect. Oil pressure senders fixed the oil gauge issue, steady as a rock now. found 2 grounds on the back of the engines that needed to be repaired and cleaned. That helped the tachs, but still fluctuate above 3500 slightly. Engines are running very smooth.