My fuel gauge on my 71 GS 455 would not read past 3/4 to full even on a full tank. This led me on a wild goose chase. I've read so many posts regarding fuel gauge/sending unit problems, done all the necessary tests in the hopes of figuring out what was wrong. I couldn't find one post with my exact issue. I was looking for the voltage reading at the sending unit. Fortunately I have another GS and checked the voltage at the tank and it too was 8.5 volts so Im going to assumed that was the correct voltage. So that put me right back to my initial problem. I purchase 2 tank units, the first unit was purchased from Bob's Chevy' on Ebay and the second was from Tamrazs. They are identical. Bobs Chevys lists the unit as (1971-72 CHEVY BUICK OLDS PONTIAC BIG BLOCK GAS FUEL TANK SENDING UNIT, DUAL LINE) and Tamrazs lists the unit as (SNDG UNIT 71-2 A-BODY DUAL LINE). We all know that a lot of GM parts are interchangeable. So with that said, I purchase another unit from Autozone (Spectra #FG91D). That part is also listed on Ebay along with a photo. I know photos aren't exactly what you might be getting but as I looked at the unit, it appeared to be a bit different. After I got the unit I matched it up to find that the arm/float/resistor portion actually sits lower than the 2 previously purchased units (approx 1") which also meant that those 2 other units actually were hitting the top of the tank (which I had suspected all the long). Being off 1 was the reason why the float wasn't traveling the full sweep of the resistor. I installed the Spectra unit and began refueling the tank (on the ground) and watch the gauge travel as I put the fuel back in. As I got to the mark I stop to look at the gauge, and then began refueling. Sure enough, she began to sweep past to eventually to full. I've attached a few photos. So, rule #1, never throw away old parts until your sure its the correct functioning part which was my first mistake, rule 2, have patients (something that I dont seem to have as I get older) and rule 3, (most important of all) be sure of what some of the aftermarket companies say (that they fit Chevy, Olds, Pontiac and Buick). My opinion, the first 2 units looked identical to my original unit but was obviously the wrong part. It also looked to be better constructed. The only issue I had with the Spectra was for some unknown reason I had to remove the sock and re-position the pick-up tube ever so slightly (first 2 units have a flexible material sock but the Spectra has a solid plastic sock/pick-up). Other than that PROBLEM SOLVED! One other side note, my 1974 Chilton's manual says the Buick 455 fuel capacity of 25 gallons, my ownersand all of my Buick manuals show it being 20 gallons. The 74 Chiltons manual also shows some of the 1971 Chevys (Nova, Chevelle, Camaro and Monte Carlo) as having anywhere between 16-19 gallons. Some other places show the Chevys big blocks as having 23 gallons. Just very conflicting information.
What I found with the Spectra sender is that the lines hit the trunk floor and make the tank teeter totter against them when I put the tank up in position. It would hit the lines before hitting the fuel tank braces. I found that the Spectra senders lines were "taller" than the OE or the other replacement I used. From the pics, it looks like the issue hasn't been resolved on Spectra's end. Just curious if you noticed the issue I had
I didn't have a issue like that, I guess they may have fixed that issue. I didn't have or felt the teeter totter effect. The tank went back into position with no problems. Only issue I had was the pickup assembly was hitting the bottom of the tank because they don't use the flexible type socks. They really should. I just had to tweak the steel line just a bit.
I know those is an old thread, but I've searched everywhere. I have seen that if your needle is past the full Mark and past the hot light, then it's the sending unit. I know there is a tan wire and a ground wire. I checked both. They seem to be good. So that leads me to the sending unit. Well after searching I've discovered the spectra units with two different part numbers; FG91C and FG91D. both say it's for a 70-72 Skylark. Anyone that has experience on this? P.S. the OP has a good picture with measurements, but he didn't exactly say what part number. (From what I've read)
I tried the FG91D in 2015 and found the unit did not read right ...full tank showed 3/4 full and quarter tank read at the bottom mark. I gave up and pulled the unit back out and reinstalled original. I was chasing a different problem and it turned out not to be the sender. My car is a 71 Skylark Looking at the original pictures on the OP, the unit with the white float resembled my 91D unit. Hope this helps in some small way. John
