67-72 Chevy Truck fuel gauge diagnostics 101

[Sparkys66]

Hi guys, this is my first post and the fuel gauge in my blazer is driving me nuts.

I purchased a new gauge and sender for the blazer and did all the testing shown on page 1 of this post. Everything was spot on with the readings so I decided to go ahead and hook everything up while on my bench. at .8 ohm's the tank read empty. as the ohm's increased the needle on the gauge started to move, but once I raised the float arm to 1/4 or 22.5 ohm's the needle was already on full. If I lift the float arm anymore than 1/4 tank the needle continues past full. The sender reads true and so does the gauge. The other bummer is I had to install everything in the blazer so I could not only use the vehicle but know when to get gas. when the needle starts to drop below full, I find a gas station quick. any ideas would be great.

Mark

[67 Burb]

Originally Posted by Sparkys66

Hi guys, this is my first post and the fuel gauge in my blazer is driving me nuts.

I purchased a new gauge and sender for the blazer and did all the testing shown on page 1 of this post. Everything was spot on with the readings so I decided to go ahead and hook everything up while on my bench. at .8 ohm's the tank read empty. as the ohm's increased the needle on the gauge started to move, but once I raised the float arm to 1/4 or 22.5 ohm's the needle was already on full. If I lift the float arm anymore than 1/4 tank the needle continues past full. The sender reads true and so does the gauge. The other bummer is I had to install everything in the blazer so I could not only use the vehicle but know when to get gas. when the needle starts to drop below full, I find a gas station quick. any ideas would be great.

Mark

Hey, Mark, what is the resistance of the sender with the float all the way up? (As in full tank.) Is it around 90 Ohms?

[Sparkys66]

Hi Bob, yes float all the way up reads 90 ohm's.

[67 Burb]

That sender will work properly with a GM gauge. What gauge did you buy? It sounds like it is not a match with your sender.

[Sparkys66]

i purchased a stock replacement gauge for my 72 blazer.

Mark

[67 Burb]

I'll set up a fuel gauge on the bench and see if I can duplicate your readings.

[67 Burb]

Mark, I tried everything, but could not duplicate the readings you are getting. I agree with Tom that you could have a bum gauge.

[TBONE1964]

Originally Posted by Sparkys66

i purchased a stock replacement gauge for my 72 blazer.

Mark

When you say stock replacement, are you talking used OE, NOS or new aftermarket. Most of the new aftermarket gauges do not require the stock style porcelain resistors. If you are using the stock resistor on an aftermarket gauge, that might be your problem.

Depending on where you bought the new fuel gauge, was the needle removed for paint and not put back on in the correct position?

Just some thoughts.
Tom