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Hey everyone, I’m new here. My names Chris and I recently just bought a 1994 GMC Suburban which I use as my daily driver. I noticed that the gas gauge has not moved since I bought even though I filled it up with $110 worth of gas. It stays about a 1/4 above the F indicator no matter what the fuel level is. All the other gauges except for the temperature gauge are working so I know its not a fuse. I noticed when the ignition is turned off, the gauge will drop down a little closer to the F marking but it never goes down any further. Once the vehicle is restarted it springs back up 1/4 past the F. Any ideas what is causing this? I was thinking fuel sending unit however it seems strange that the gauge doesn’t move all the way down past the F when the vehicle is turned off. I am assuming its supposed to as it does move down somewhat.
Is there some kind of test I can can do before I pull the sending unit out? The bottom of this truck has seen better days and there is lots of rust. I know that I’m gonna have a bad time trying to get the rusted fittings off the sending unit and probably even getting the gas tank straps mounting bolts loose. Is there a way I could trick the gauge into thinking the tanks empty so I can see if the needle is even capable of moving down below the F. Possibly its jammed or something. Thanks for you help. Also if I have to pull the tank. Any tips or tricks for getting stubborn rusted bolts and fuel lines loose?
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Here is instruction right from AllData:
Gauge Stays at Full or Beyond
This condition is generally caused by a open circuit between the gauge and sending unit.
Disconnect sender lead at fuel tank, then ground lead and turn ignition switch to the On position.
If fuel gauge reads empty, replace tank sending unit.
If gauge reads at full or beyond, locate and repair open in circuit between gauge and fuel tank. If circuit is satisfactory, replace gauge.Any tips or tricks for getting stubborn rusted bolts and fuel lines loose?
If it’s really that bad, I would purposely try to break everything, and replace everything that broke.
Start soak treating your rusty goodness 2 or 3 days prior to starting the job with PB Blaster. Use air tools when necessary. For fuel system work, I would not advise the use of torches to heat rusty fasteners.
which I use as my daily driver. I noticed that the gas gauge has not moved since I bought even though I filled it up with $110 worth of gas.
:ohmy: !!!
Thanks Wrench Turner for that helpful information. It will come in very handy. Does All Data list which exact color wire I need to ground? Looking at that diagram it appears that there is at least two wires going to the sending unit. I assume one is a ground and I couldn’t hurt anything by grounding that but I just want to make sure before I do it. Thanks again
Regardless of whether it’s a 2 or 3 pin connector, you can jump every pin on that terminal together and get the results you are looking for by making sure every pin has a chance to go to ground.
So, you don’t even have to know which one is the ground wire… but you’ll know that one of them is the ground wire and therefore, the circuit will be grounded. You can probably do all this with just paperclips. 🙂
Well I grounded out the plug and the gauge went all the way Down. Looks like I will be pulling the tank. Thanks a lot guys for the help.
Well done with the diagnostic help Wrench turner. I too thought it might be a sending unit and it appears your testing has confirmed that. A suggestion if I may. It’s no secret that GM’s are known for fuel pump issues. If it were me I might just change out the fuel pump at the same time as the sending unit as a ‘preemptive strike’. This could save you time and effort down the road. Keep us updated on your progress.
Just wanted to give you guys an update. Sorry for this being so long. First off big thanks to Wrench Turner and College Man. You guys helped point me in the right direction. The truck came from NJ and unfortunately for me the chassis and everything else has a nice coating of surface rust. I believe it was probably used as a boat over in NJ. I started the job Friday night of removing the tank. I siphoned out almost 20 gallons of gas. I really expected it to have a lot less gas in than that as I did drive it a lot.
I coated the tank strap bolts on Wednesday with liquid wrench and than resprayed them on Friday. I got them both to spin without breaking and I thought I was out of the woods. Unfortunately they just both kept spinning. They went through the frame and there was a nut on top that I believe was supposed to be attached to a clip to hold the nut from spinning. Well that didn’t work so well and I spent longer than I really should have trying to get them out.
After spending way too much time on these bolts I made the decision to have to cut them out. Scary as it was, it was pretty much my last resort. I brought a box fan and aimed it at the tank to help blow away the fumes and started cutting. Eventually with the aid of a big hammer, they gave up the fight and I managed not to blow myself up. The next hurdle was getting the tank loose from the frame. Even with the straps removed, it would not budge. I believe even if the tank was full of gas (30 gallons) and I drove the truck down the bumpiest road that the tank never would have let loose. It was on there that good.
It also gave in after I had at it with a pry bar. I made lots of progress prying from the rear of the tank down. The sending unit was so rusted up, I inadvertently broke one of the metal lines that come out from the sending unit. I than purposely broke the other. Once the tank was out of the way, I was able to get two line wrenches on what was left of the fuel fittings and get them out. Once the tank was out, everything else went smooth as silk. The inside of the tank was in amazing condition. Oh, by the way, when I was taking the tank out I heard something metal rattling around in it. Any guess what it was? The fuel sending unit float arm was laying in the bottom of the tank. It appears the little plastic tab that go on each side of the float arm broke off .
I installed the new sending unit, went to tractor supply and bought two long bolts with washers, lock washers and nuts. I reinstalled the tank enough to hook up the electrical connections to test the sending unit and voila, my gas gauge read correctly. I did want to replace the fuel pump at the same time, however I am so broke right now even the sending unit was a hard pill to swallow so I couldn’t do that at this time. On the plus side, I have got brand new bolts and nuts in there with anti seize so if and when the pump fails, I shouldn’t have nearly as hard as a time that I did this time getting stuff loose.
So all in all I got it done. The rust made it much harder than it should have been but we all know how that goes. I would say I spent 6 hours on it. Probably half of that was fighting with the bolts and the other half was siphoning the gas out into little containers.I was also able to check my coolant temp switch the same way by grounding it to the frame. It also was not working. Now I replaced that and all the gauges are working.
Thanks a million Wrench Turner and College Man. You guys really help me get this problem solved. Also Eric, thanks for all the helpful videos you make. I learn a lot from watching your videos and appreciate you taking the time to make them.
glad to hear everything turned out good.. and at a much cheaper price than having someone else do it for you 🙂
getting that gas tank empty is a big help when doing fuel pumps/sending units. sometimes it’s hard to do but if you gamble right and you bring the truck home on fumes the job becomes a lot easier.
btw, glad you didn’t blow yourself up. I like to break out the ol’ bolt cutters when breaking old rusty gas tank stuff. I try to stay away from the sawzall, die grinder, and torches.
**Do not catch yourself on fire** :side:
Q: how difficult was it to remove that rusty lock ring?
Glad that we could help. Glad to hear that it all worked out.
Thanks for the update. I bet you feel good every time you look
at those working gauges. 🙂
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