Fuel gauge fluctuations

[egchewy79]

I’ve posted this before, but does anyone have a fuel gauge needle that fluctuates as much as 1/8-1/4 tank? When I start my car, fuel level is at a certain amount, but as soon as I start driving, it seems to drop abruptly by anywhere between 1/16-1/4 tank. There’s some fuel in the return line, but probably not 1-4 gallons. Is my fuel getting aerated and the sender isn’t about to get an accurate read? This video is the last recorded fuel level after turning off the car and again after going into the accessory position on the ignition switch. Next pics are fuel level after driving 5 miles home.

https://youtube.com/shorts/MOCVspaMi...N0E1x6Ri14x5YiIMG_5813.jpgIMG_5814.jpg

[F500guy]

So, I can say I have fuel gauge issues and have not left the garage...I put 2 gallons in the tank the other day to get ready for my first start, gas gauge went to nearly 1/4 tank. Well, next day I was playing around and the gas gauge is stuck on zero now. So, bizarre behavior for sure.

[egchewy79]

Have you calibrated your gauges yet?

[JJK]

I posted a similar concern a few months ago and the general consensus was the fuel level sender-gas tank-gauge combination for these car leads to a lot of slosh in the tank with a sensitive fuel level sender. I read that 90s mustangs has a fuel module that would dampen the signal, but I think those are hard to come by now. I would love a solution though .

[Rdone585]

I remember a guy in high school who had a Chevelle with a manual tranny and a 454. All the other students that knew him wanted to get a ride. When he punched it the gas gauge would go from a half tank to empty, from the acceleration. So he charged the "riders" for the gas they used :-) in giving them a ride. At the time high-test / premium was $0.99, so they had to pony up about $7 for that "thrill ride". Ahh, the good-ole-days.

[PG_Cobra]

I just fixed this problem with my Speedhut gauge. My gauge would keep fluctuating to various levels even without the engine running. I complained to Speedhut and returned the gauge. They did some wiring changes and returned it to me. The problem persisted. I disconnected the gauge from the sender unit and inserted a 100 ohm resistor into the gauge wiring. The gauge was rock steady. I put my ohm meter on the sender unit terminals and watched. Every few seconds the resistance would jump to a different value. The bad part was the sender unit. The Speedhut gauge has slosh control in the electronics so the jumping sender unit shows as a slow movement on the gauge. I got a new sender unit from LMR and avoided the cheapo generics. So far, so good. Gauge seems to be steady and accurate. Hope this helps.

[egchewy79]

I’ll look into the sending unit. What ohm range works with the speed hut gauges?

[edwardb]

I’ll look into the sending unit. What ohm range works with the speed hut gauges?

If you have the usual Mustang tank, the common sending unit is 16 ohms empty, 158 ohms full. The Speedhut gauge will calibrate to other values. But for fitment purposes, I'd stick with a sending unit made for your specific tank.

[weendoggy]

Sending units and gauge need to be in the same parameter. If you have a "Fox Body" fuel tank, you can use a 83-86 sending unit, which is 73 ohms (empty) and 10 ohms (full). I use Autometer gauges and the EFI sending units don't match to their gauges. I recently sent my gauge to AM to be checked/repaired. They offer a new replacement at 1/2 cost. Most of the EFI units are 22 ohms (empty) and 145 ohms (full). fyi