When I bought my 06 f150 4.6 the fuel gauge wasn't working. I just replaced the fuel pump assembly and sending unit, and fuel filter. The gauge worked when I out gas in it then slowly went back down to E. I checked the connection of the wiring harness under the driver door on the frame and everything was solid. I did a gauge sweep test and everything worked. My mechanic even hooked up a scan tool and said all the gauges are working fine. I just started the truck again and the gauge went up to where it should be. Any ideas of what I should do? I'm hoping the gauge works permanently now, but if it doesn't what should I check next? My mechanic said I may have gotten a bad fuel pump assembly.. the brand was Airtex. Thanks!

 

Add some shots of MMO to the fuel, the float is probably sticking.

 

Well it's brand new. Could it still stick? Sorry but what is MMO?

 

duked must of miss the replaced the pump assembly part.. i’m thinking you may have a cluster problem but, the sweep test says no...

 

I definitely did miss that part.

 

I believe MMO is Marvel Mystery Oil.

 

Yes, MMO is Marvel Mystery Oil.

 

Bringing this back to life to say thank you!!!! Immediate fix!

 

what year is your truck?
are you saying MMO fixed a stuck float/fuel gauge for you?
what ratio did you mix/use ?

(too bad OP never closed this out with solution)

 

07 5.4
I don't know how this got posted in the wrong thread but what fixed mine was removing the little black box that is on the fuel pump connector. It is essentially the box that allows for the use of e85/flex fuel