Oil Pressure Gauge Pinned
 

I have a 29' Fountain with twin 454 Mag MPIs and my oil pressure gauges stay pinned as soon as I turn the key. I changed the oil pressure sending unit, but the gauge still goes from zero to pinned as soon as i turn the key. I am thinking there is a bad ground, but I am wondering if anyone else has had this problem before and what they did.

I think you may have a short to ground in the sender wiring cause if you ground the sender wire the guage should peg

Actually the wire going from the sending unit to the gauge may be grounding somewhere in between. Try disconnecting it and start it and see if still does it. If it does than either the wire is grounding somewhere or it is in the gauge it self.

That was my thought, I would check the guage & wiring by grounding the lead at the sender.If you unhook the lead & turn the key it should read zero if not check wiring. you can check guage the same way by grounding the sender lead. I have found chaffed insulation around studs or other sharp edges

If you used sealer on the sender, it may not be grounding properly. The sender grounds itself to the engine block. It could also be bad ground on the back of the gauge.

Thanks for the feedback. I will let you know what I determine.

If you changed gages you could have the wrong polarity sending units.

x2 it must be a short, a open would be "0" psi.

That would depend on if the gage is sinking or sourcing.

Fixx
 

all the above!!

did you have any stereo work done??? i have seen some people ground a head unit to the gauges and hooked to the wrong wire..ma be put speakers in with 3'' drywall screws and through a wire harness....i have seen a bunch of weird mishaps..

+100 :drink:
good luck

Fixx
 

? are both engines doing the same thing?

That's why I figured it was a polarity issue mrfix.

The gauges are stock Gaffrig Gauges and both port and starboard oil pressure gauges are doing the same thing.

I agree, I have seen gages float before, seeking a ground. When you turn different things on or off the gages would change. But to peg out as soon as you hit the key would almost have to be a dead short. Very strange both engines would be doing the same thing. Take a meter and see if the sender wire is shorted, at both ends. I believe the senders are 0-88 ohms, get some resistors and connect them from the sender wire to ground.

Fixx
 

did you use gaffrig senders?? they have their own senders for their gauges or they will be off when reading them.

mrfixxall you are the bomb!!! I have seen all kinds of wiring clusterf@cks in boats & cars. If both guages are doing the same thing & senders & guages are the same, stereo? speakers? good question I have seen with custom vans they screwed the panels & such right through wiring harnesses & with boats the pounding they take people put longer screws in the speakers that is why I mentioned sharp edges or studs

did you start the engines ?? may be normal without running ?

Absolutely!! I had sealer on the NPT and I was goin crazy!!!! Then I gave it a little tweak and I had a normal functional gauge!!:drink:

Good call Griff, sounded like a short to me.

If you take the lead off the sender and see if it pegs or stays at 0, then go to ground and see if it changes. If that gets you to go from 0-pegged then you do not have a wire issue you have a sender issue. If when you run this test it does not work then do the same test at the back of the guage. If it works there you have a shorted out wire and you will have to run a test on the wire.

i didnt read the entire thread if this is a repeat.........
don t reuse a guage that has been pinned it is only good for the garbage can

I just got time to test what my problem was because the boat was in storage. I disconnected the wire from the sending unit and turned the key and the gauge still goes to pinned. Then I connected the wire back up to the sending unit and disconnected the sending unit lead on the back of the gauge. I connected the lead on the back of the gauge to ground and gauge goes to zero. I also put a 2.2k ohm resistor(only one I had in at home) in series with the gauge and sending unit and the gauge read just under 20 PSI. Not to sure what this means yet because I thought the gauge went from 0-88 ohms

I just went out to the boat and bypassed the orginal wire from the sending unit to the gauge to see if there is a short in the wire, but it appears to be doing the same thing. Any thoughts?