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kjohnson
01-25-2009, 04:27 PM
My gauge has always read half full (or half empty for you pessimists). I replaced the sending unit and the gauge still reads half full. I assume the gauge is bad. Will one of the teflex gauges from West Marine or Boater's World work? I assume I just need a 12 volt gas gauge? I can't find a new MC gauge for a 94 anywhwere. Thanks for anyone who knows the answer.

Footin
01-25-2009, 04:39 PM
If you take the two wires at the sending unit and touch them together it should peg the guage to full. If it reads full the gauge is fine.

kjohnson
01-25-2009, 05:19 PM
Thanks Footin, I'll try that.

Gamble
01-25-2009, 06:55 PM
If I had to bet, the sending unit is your culprit..........perhapss the diodes in there that adjust to make the gauge read correctly are shot. You can get one that is adjustable to the tank depth, and that should work for you if you confirm it's the sending unit.

kjohnson
01-25-2009, 09:08 PM
Gamble,

It is a brand new sending unit. I guess it could be defective, but does that seem likely?

Muttley
01-26-2009, 01:08 PM
I would bet it's the sending unit. The float is probably sticking.

flipper
01-26-2009, 01:39 PM
Most of the time the gauge will work or not, not read 1/2 tank or something like that. Do like Footin said and check it before you buy anything. Check the wires on the gauge itself too. Is the new sending unit is the right size? Does it read 1/2 all the time (Whether the tank is empty or full)?

mad-dog1
01-26-2009, 01:55 PM
New sender Ohms resistance vs. gauge might be wrong maybe??
0-90 Ohms,10-180 Ohms,240-33 Ohms??
might want to look in to that ...maybe..
Good luck!

thatsmrmastercraft
01-26-2009, 02:49 PM
I haven't done this with the Mastercraft fuel sending unit but have with cars. With the sending unit out of the tank and plugged into the wiring, simply move the float through its travel and watch the gauge.

kjohnson
01-26-2009, 04:28 PM
Most of the time the gauge will work or not, not read 1/2 tank or something like that. Do like Footin said and check it before you buy anything. Check the wires on the gauge itself too. Is the new sending unit is the right size? Does it read 1/2 all the time (Whether the tank is empty or full)?
It always reads 1/2 full.

flipper
01-26-2009, 04:38 PM
Even with the key off? Never moves at all right? I'd say either it's not getting power, or you're right, and the gauge went bad on you.

thatsmrmastercraft
01-26-2009, 04:45 PM
OK, all the below zero weather and whisky (for medicinal purposes only) this weekend has my thought process slowed to a crawl. Footin has it right on checking the sending unit, but if you want to go one step further, you can check the resistance of the sending unit with an ohmeter connected to both leads of the sending unit. Without knowing the resistance values, you can at least move the float through it's range of travel and watch the resistance change. That will also establish that the sending unit is faulty or not.

Bruce
01-26-2009, 04:51 PM
Mine never reads less than half. I consider that a real plus. I never have to run out of gas!!

flipper
01-26-2009, 05:01 PM
Mine never reads less than half. I consider that a real plus. I never have to run out of gas!!

Let us know how that works out for ya:rolleyes:

kjohnson
01-26-2009, 06:21 PM
I tried the wire test. It pegged at empty the first few times. A few times it did peg at full. Any ideas as to what might be the matter?

thatsmrmastercraft
01-26-2009, 09:15 PM
Time to start checking the rest of the connections for marginally high resistance. You might still have a bad sending unit, but there appears to be some corrosion there somewhere. Clean every connection - even the ones that look good. I have been battling corrosion at the fuse block, but my boat is considerably older.

kjohnson
01-27-2009, 10:22 AM
I think it is the sending unit too, even though it is new. Either the repair shop put in the wrong sending unit, it was defective or the float is sticking. I am taking it back to have them check it.