Fuel Gauge

[bstock1962]

Originally Posted by mister.freeze

I can reach the tan wire and disconnect it easily enough. But yes, to access the sender, I havve to drop the tank, which is easy enough when empty. That's why the delay until next week: it will be close to empty from commuting all week.

What's best to clean the sender? Carb cleaner?

Mister.freeze, I've done carb cleaner and brake cleaner both. On the last one I ended up using engine degreaser because of the varnish crud. If you do that be sure to read the can warnings in case you can't apply to plastics or whatever. In other words be careful.

[mister.freeze]

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.

[slikside]

sub'd.

[mister.freeze]

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...

[mister.freeze]

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.

[bstock1962]

Originally Posted by mister.freeze

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.

Sounds like a ground problem for sure now. My c10 pickup sending unit doesn't have any screws to attach to. If your new wire is grounded good, I'm betting you'll start seeing the gauge needle move. Where did you attach the other end of your ground wire? I think you still want to make sure the fuel tank is grounded good too.

[bstock1962]

HDIXON, any progress on your fuel gauge problem?

[mister.freeze]

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...

[bstock1962]

Originally Posted by bstock1962

Sounds like a ground problem for sure now. My c10 pickup sending unit doesn't have any screws to attach to. If your new wire is grounded good, I'm betting you'll start seeing the gauge needle move. Where did you attach the other end of your ground wire? I think you still want to make sure the fuel tank is grounded good too.

After re-reading your previous symptoms, I need to retract what I said about it being a grounding problem. If it was a ground issue, your gauge would go to 3:00 again. So, assuming the gauge still goes a little past full (and sender works fine outside the tank) it seems like your float/sending arm might be getting stuck on the inside of the tank internally. I'm not familiar with the blazer fuel tank, but is there any room to rotate your sending unit a little to make sure the arm/float clears the internal sides of the tank? Something is causing it to bind up. PIA to troubleshoot when you have to drop the tank....

[bstock1962]

Originally Posted by bstock1962

After re-reading your previous symptoms, I need to retract what I said about it being a grounding problem. If it was a ground issue, your gauge would go to 3:00 again. So, assuming the gauge still goes a little past full (and sender works fine outside the tank) it seems like your float/sending arm might be getting stuck on the inside of the tank internally. I'm not familiar with the blazer fuel tank, but is there any room to rotate your sending unit a little to make sure the arm/float clears the internal sides of the tank? Something is causing it to bind up. PIA to troubleshoot when you have to drop the tank....

Also, if your sending unit wiring is long enough, test the function of the sender with the tank still sitting on the ground. You will have to take a piece of wire and ground the top of the sender or it will still show 3:00. Easier than taking the tank in/out repeatedly. Mess with the position of the sender until gauge goes to empty (assuming you drained it).

[mister.freeze]

the sender is in the same position it always was. I just don't get it. The float and arm have nothing to bind against. Tan wire disconnected gets me the 3:00 position, grounding the tan wire gets an empty reading. If the float wasn't floating, I'd get an empty reading.
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.

[VetteVet]

Originally Posted by mister.freeze

the sender is in the same position it always was. I just don't get it. The float and arm have nothing to bind against. Tan wire disconnected gets me the 3:00 position, grounding the tan wire gets an empty reading. If the float wasn't floating, I'd get an empty reading.
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.

Test your sender wire by touching it against the tank. If the tank is grounded then the gauge will read empty. I gather you've done this.


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?

[mister.freeze]

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?

[VetteVet]

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Originally Posted by mister.freeze

I've done continuity checks between the tank, flange, and frame. All are connected.

Your grounds would appear good all the way to the fuse panel, but your reading on the gauge indicates that you aren't getting a ground from the sending unit to the fuse panel and on to the gauge. Have you run a ground from the fuse panel FUEL terminal to a good ground ? This would give an empty reading as would the sending unit wire if the float is down as you indicate.The gauge should also be grounded to the cluster tin and that should be grounded. This thread will be really helpful to you.

http://67-72chevytrucks.com/vboard/s...d.php?t=640615

If the float is too heavy, or not floating, I'd get an empty or near empty reading. I'm getting full + 1/2".

Again this is a non grounding problem. The gauge is not seeing a ground via the sending unit wire. It is not getting the variable ground through the sending unit resistor.

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?

The sending unit resistance range is 0-90 ohms 0 = empty and 90 = full so more resistance means more gas.

[bstock1962]

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?

[1968_K20_4x4]

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

[mister.freeze]

Originally Posted by bstock1962

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?

The sending unit is positioned as it always has been: no obstructions to movement, same screws, etc. I'll check ohms between the top of the sender and where the tan wire connects. Haven't done that yet. I should get anything less than 99 ohms as the tank is NOT full at this time.

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!

[slikside]

Originally Posted by mister.freeze

The sending unit is positioned as it always has been: no obstructions to movement, same screws, etc. I'll check ohms between the top of the sender and where the tan wire connects. Haven't done that yet. I should get anything less than 99 ohms as the tank is NOT full at this time.

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!

You sure can. I just did this myself. I got mine from GMC Pauls with several other things I ordered. Not sure if any of the big parts places carry them. I did find the sending unit sock/filter at a local "old time" auto parts store, and it wouldn't surprise me if that type of store had a float in stock.

[bstock1962]

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!

[bstock1962]

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.

[mister.freeze]

Anybody know the correct part number for a Blazer sending unit?

[mister.freeze]

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?

[bstock1962]

Originally Posted by mister.freeze

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?

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)?

[bstock1962]

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.

[mister.freeze]

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.