I took my sig truck out for a drive today. I put in 13 gallons of unleaded and hit the highway. My gas gauge isn't working so I set the trip odometer to 0. I was doing about 60/40 highway and city driving and I never went over 65mph. Power and throttle response was normal, transmission shifting fine, and engine was running like a champ. I drove around for a while running errands and I pulled into a drive guru and shut it off. After I ordered, I started it back up and it got about 50 feet running fine the suddenly it sputtered and died. I started it back up thinking maybe the fuel had sloshed because there was a steep incline I just went on. It fired up but I only got about ten feet to a gas pump. When I was back on flat ground I started it up and it ran for about 30 seconds with me holding the throttle about 1300 rpm. While holding the throttle pedal steady, the rpm would suddenly drop to about 1100 for less than a second and then go back to 1300. It dd this for about 30 seconds before I let off the throttle only to sputter and die again. I looked down and I had only gone 83 miles! That comes out to roughly 6 mpg. Last time I had the same driving time in the same environment in this truck I averaged 10.3 mpg. I put in another 6 gallons and drove home. I talked to a few people and I was told it could be the fuel pump going out causing it to suck in air at 1/4 tank or less. Did I kill my pump trying to get it to the station on fumes? Or is there something underlying that I'm not aware of? I know this 460 is thirsty but 6 mpg? I've never gotten less than 8 before. Last week I put in 14 gallons and went 170 miles with a little left to spare. Why the sudden loss of mileage? The truck only did this one other time about 3 months ago and it hasn't done it since until today

 

Maybe just low enough that you got below the pickup point? 6MPG is possible, but I would more likely bet that you just drew the tank down further than you normally would have and got below the inlet to the pump.

 

If your gauge is broken, how did you know how much fuel was in the tank each time you added more fuel? Unless you run out of fuel each time you pull up to the station, you really have no clue what is in the tank when add more fuel. When you say you've never "gotten less than 8 before", maybe you had more fuel in the tank than you thought. Plus, doing the math - you put 13 gallons in, if you got 8 MPG (which apparently you've done before), that would equal 104 miles, and you sputtered at 83 miles, so that's only a difference of 21 miles. I mean, there are enough parameters in your situation that can skew the numbers just a little bit (how much fuel was really in the tank when you filled up? How much fuel was in the tank when you figured out your previous gas mileage figures? etc, etc) that would easily account for a scant 20 miles. With a 460, driving conditions which might not even be considered could account for some discrepencies as well - like driving into more wind than the last time you figured you mileage.