I bought a 1986 4cyl fiero as a project last fall. It had been parked about 15 years earlier with a full tank of gas because the fuel pump had gone out. The whole fuel delivery and return system was in BAD shape. All of the fuel lines were very clogged, Satan himself had been living inside the tank , all the rubber on the fuel pump had disintegrated, and the fuel level sending unit was badly damaged by the gasoline. I had the tank professionally coated and cleaned, I cleared out the clogged fuel lines, and I put a new fuel pump in. I couldn't find a reasonably priced fuel level sending unit online, so I just used the old one to hold my fuel pump in place and decided I could go without a working fuel gauge. I wasn't getting power to my fuel pump through the original 3 wires that ran from the engine bay to the sending unit , so I decided to bypass it all and power the fuel pump with a 12v + wire from a fuse splice in my fuse box and ground the -. I ran my Fiero like this for a while until I found a level sending unit at a u-pull-and-pay. I took it all back apart, and when I was in the process of messing with the new (and slightly different) sending unit I mixed up the wiring that resides inside the tank. I (stupidly) began messing with the wiring and applying 12v to different wires to see what wires powered what. At one point during that process I saw a wee bit of smoke come from the sending unit. I eventually figured the wiring out that resided inside the fuel tank. I connected the sending unit to the original 3 wires that I had previously bypassed because I had fixed the wiring issue with the 3 original wires, and I was getting power through them. I got rid of my homemade fuel pump wiring and I re installed everything just as it was supposed to from the factory. The fuel pump worked, but the gas gauge didn't. I just assumed I had fried the electronics in the sending unit when I had seen the smoke. I just gave up on having a working gas gauge, and began driving it just as I had before. About a week after I had attempted to install a working sending unit the gas gauge started working. It worked for a few weeks, then the needle on the gauge went back to showing much over the full mark, like it had when it was broken. It has been working intermittently ever since. However recently it has been fixing itself and breaking again multiple times per day. It will usually fix itself when I accelerate hard, and then stop working again a few minutes later. I find when I hit a bump it will usually either start working or stop working, depending on whatever state it is in when I hit the bump. Sometimes the needle on the gauge will move back and forth for a while like it cant make up it's mind on whether to work or not. The gauge will never begin working or stop working when the vehicle is parked and running, only when I am driving. Because the gauge's state of operation only changes when movement is involved, I have been led to think that the brown wire that sends information to the gauge has a faulty connection, or is intermittently grounding somewhere. However I don't know if my problem is stemming from the smoke that I saw come from the unit months back. Have you guys ever seen a faulty sending unit act like this? or do you believe that I have a wiring issue? I would like your input before I dedicate another Saturday to getting under the car and dropping the tank... AGAIN. Also if you know where I could get a good condition used or new sending unit, I would appreciate if you could relay that information to me.

Is there a merit badge for reading through the whole paragraph?....

I have not seen your particular problem before.
Perhaps you broke a wire in the sender wipe windings.

Fuel Tank Sending Unit Solution!

https://www.fiero.nl/forum/Forum2/HTML/132065.html

[This message has been edited by Gall757 (edited 05-19-2015).]

Consider yourself fortunate that you got to see the smoke and tell us about it. Others have met the lord during this style of testing. I'm glad your still with us. Ok moving right along, I believe Jegs or Summit Racing sells a universal sending unit that works in the Fiero.

Check them out and pick up a multimeter at Harbor Freight or Radio Shack while your at it. It could save your whole day.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

Well i had the sending unit out of the tank and well away from any combustible ls when i was messing with the wiring when i saw the smoke. So i dont think i was that close to seeing the lord haha. I will check out the universal sending units.
Thank you