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#26 | |
Registered User
Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Quote:
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#27 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
I've been driving it at about a tank a week since the end of July. You'd think all that gas would have cleaned it up by now. I'll ground that tan wire tomorrow and report back.
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'72 K5, known as 'the Fox.' |
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#28 |
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Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,162
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Re: Fuel Gauge
sub'd.
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1972 Chevy C-10, SWB, Fleet, 350/350, PS, PB, HEI, mostly stock, Survivor. ![]() |
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#29 |
Registered User
Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
Grounding the tan wire DID make the gauge read empty (most that needle has moved in years!). Last time I had the sender out was in 2000. Guess I know what I'm doing this weekend. I hope all it needs is some cleaning...
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'72 K5, known as 'the Fox.' |
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#30 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
So I got the sender out. It didn't look bad, but I hosed it down with carb cleaner anyway. I clamped the flange to the frame to simulate a god ground, hooked up the tan wire, and moved the float manually. The gauge moved! Up and down, like it should. So I put it all back together and.... nothing. Just like it was before. Well, I had to get to work, so I tanked up.
Last night, I added a ground wire to one of the screws holding in the sender. I'm hoping it's just now reading the full tank, but I'm not too optimistic.
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'72 K5, known as 'the Fox.' |
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#31 | |
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Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Quote:
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#32 |
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Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
HDIXON, any progress on your fuel gauge problem?
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#33 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
I used the same stud that I clamped the sender to. Not too sure how to ground my Aero tank other than what I've already done...
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'72 K5, known as 'the Fox.' |
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#34 | |
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Join Date: Aug 2016
Location: Idaho
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Re: Fuel Gauge
Quote:
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#35 | |
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Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Quote:
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#36 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
![]() The tank and top of the sender are both grounded. There seems to be a fixed resistance in the sender, but the sender works outside the tank. ![]()
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'72 K5, known as 'the Fox.' |
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#37 | |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,714
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Re: Fuel Gauge
Quote:
Test the sending unit by touching the flange with the sending wire. If the gauge still reads empty then it means the sending unit is grounded to the tank and to the frame and that means the sending unit resistance is not varying. Because it moves the gauge outside the tank when you raise and lower the float then the sender resistance is varying, which leaves the conclusion that the float isn't moving inside the tank. Have you checked the float itself for pinholes and gas inside which would make it too heavy to move inside the tank?
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#38 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
I've done continuity checks between the tank, flange, and frame. All are connected.
If the float is too heavy, or not floating, I'd get an empty or near empty reading. I'm getting full + 1/2". The float may not be moving anyway, and possibly a short at the point where the arm should read empty. Which is true: more or less resistance reads full?
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'72 K5, known as 'the Fox.' |
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#39 | |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,714
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Re: Fuel Gauge
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Quote:
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#40 |
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Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Well, I'm sticking with my last assessment...that something is going wrong inside the tank causing the sending unit arm to stick in the up position (full). Everything works perfectly outside the tank when moving the arm up/down right? And tank and sending unit are grounded good right?
If you have an ohm meter, here's what I would do: With the tank out and sitting on the floor and sending unit still mounted inside, measure the resistance across the unit from the connector to the top of the unit. You should measure nearly zero since the tank is empty. The float should be all the way down (empty tank). If it still measures nearly 90 ohms, then the arm is stuck in the full position and you have a problem. Don't reinstall the tank into your blazer until your meter measures nearly zero ohms with no gas in it. Could any of the mounting screws on the sender be too long causing the float arm to bind?
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#41 |
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Join Date: Oct 2016
Location: Ontario Canada
Posts: 191
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Re: Fuel Gauge
Just wanted to say thanks guys for all the great information in this thread, I used a lot of the info here to diagnose and repair my fuel gauge issues and now its working as it should
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#42 | |
Registered User
Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
Quote:
my thoughts now are this: the float is not working, and the point on the resistor that the arm rests at when empty is corroded or otherwise providing excessive resistance. The unit works outside the tank, so the resistor is at least good at any other point. Can I replace just the float? Regardless, next time the tank comes out will be the last; such a PITA to get back in!
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#43 | |
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Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,162
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Re: Fuel Gauge
Quote:
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1972 Chevy C-10, SWB, Fleet, 350/350, PS, PB, HEI, mostly stock, Survivor. ![]() |
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#44 |
Registered User
Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Yep, floats are also available at places like LMC and Summit. However, a bad float will sink (fills with gas) and go to empty. Not sure anything would cause it to go to full except a full tank of gas.
Curious to hear what you get for resistance measurement while sender is in the tank. If it measures 90 ohms, try slowly removing hardware until it goes towards zero (or maybe hear the float drop). Also, how smooth is the float/arm movement when you move it by hand? Is it completely free (should be) or feel like it's in syrup (bad)? I would still take some engine degreaser to it regardless. It's worked miracles for me. If things go well and it seems like it's working, try only filling your tank 1/2 full and watch for gauge movement. Then later fill the tank to full again. If none of that helps I would get a new sending unit. Don't give up! You'll figure it out!
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#45 |
Registered User
Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
I agree you could be right about there being a sort of "dead spot" when the arm is in the empty position. That's where that engine degreaser could take care of it too. You can measure/test all positions of float arm when you have it out, and find dead spots if there are any. Your ohm meter will tell you everything you need to know.
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#46 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
Anybody know the correct part number for a Blazer sending unit?
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'72 K5, known as 'the Fox.' |
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#47 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
35.3 ohms as it sits, key off, between tan wire terminal and one of the flange bolts/ground. Should be 99 to make the gauge read full or mre, shouldn't it?
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'72 K5, known as 'the Fox.' |
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#48 |
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Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
Yes, I expected you would measure 90 ohms or so (bad), which would make the gauge go to full. 35.3 ohms should not be anywhere near full, more like 1/3 tank. Are you measuring with the tank still installed or is it removed and sitting on the ground (not sure if you can get your meter lead in there to measure while installed)?
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#49 |
Registered User
Join Date: Aug 2016
Location: Idaho
Posts: 42
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Re: Fuel Gauge
If you are measuring 35.3 with the tank installed, reconnect the tan wire to the sending unit then go to the fuse box and disconnect the same tan wire from the fuel gauge terminal (at top of fuse box). Measuring from that end of the tan wire to a good ground, does it measure the same 35.3 ohms?
Or, if you have the tank out and measure 35.3, start removing the sending unit hardware until you measure close to zero ohms (assuming the tank is empty). With the sending unit out, does it measure zero ohms in the empty position and 90 in the full position? It should.
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_____________________________________________ 1972 C10 - SWB /383 stroker/Th400/3.73/vintage air |
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#50 |
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Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: Fuel Gauge
That measurement was installed. Incidentally, with the tank nearly empty, the needle started to move whenever I stopped. It would go down to around 3/4 then work it's way back past full as things settled down. I put in 10 gallons and it's locked back at 1/2" past full. Safe to say the resistor is bad, and the float and arm actually work.
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