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Old 06-29-2009, 12:26 PM   #1
dfosh
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Fuel guage prob 49 gmc

I have a friend who has just completed a 49 gmc using an S10 chassis engine ,trans . Everything works great except his fuel guage .He had the orignal guages redone telling them he was using the S10 fuel tank and fuel injected engine . Any ideas as what might be wrong ? thanks in advance
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Old 06-29-2009, 01:12 PM   #2
OrrieG
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Re: Fuel guage prob 49 gmc

Most obvious cause is sending unit amperage. Older trucks used a 0-90 ohm range, newer vechicle are 75-300 ohm range. Using a newer sending unit with older guage will cause it to peg at full until you fall below 90 ohms which is when you have about 1 gallon of fuel left. When they restored the guages they may not have modifed them for the new amperage.
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Old 06-29-2009, 02:51 PM   #3
BlueJeep
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Re: Fuel guage prob 49 gmc

So do AD trucks use the 0-90 ohm sending unit?
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Old 06-29-2009, 05:18 PM   #4
dwcsr
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Re: Fuel guage prob 49 gmc

My first guess would be that the sender is 12 volt and the gauge is 6 volt
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Old 06-29-2009, 06:49 PM   #5
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Re: Fuel guage prob 49 gmc

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Originally Posted by BlueJeep View Post
So do AD trucks use the 0-90 ohm sending unit?
I believe so, although I am not sure with the 6 volt trucks. Stovebolt guys could probably tell for sure.
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Old 06-30-2009, 08:25 AM   #6
dfosh
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Re: Fuel guage prob 49 gmc

Guages were completley upgraded for 12 volts and the 4.3 fuel injected engine . Somthing could have been missed but assuming it wasent anymore ideas ?
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Old 06-30-2009, 11:31 AM   #7
OrrieG
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Re: Fuel guage prob 49 gmc

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Originally Posted by dfosh View Post
Guages were completley upgraded for 12 volts and the 4.3 fuel injected engine . Somthing could have been missed but assuming it wasent anymore ideas ?
What is it doing (or not)? Not working at all, pegging to full, stops at half full, sprodic operation? Did you use the stock S-10 tank or an after market tank? Need to narrow it down to the guage or sending unit or wiring...
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Old 06-30-2009, 10:38 PM   #8
Kid
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Re: Fuel guage prob 49 gmc

I'm not sure, but I don't think you can change the "Ohms" of a given gage. Your 49 GMC gage is a 0-30 Ohm gage, possibly converted to 12 volts, but I bet you'll need to use a after market 0-30 Ohm sending unit to make it work correctly.
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Old 07-01-2009, 06:14 PM   #9
dfosh
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Re: Fuel guage prob 49 gmc

Thanks for all the help. Kid got it right .Ohms sending unit problem . He was using S10 fuel tank .
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