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I have a truck with a full tank of gas (12-16 gallons?) that's been sitting for 12 months and I'm about to change the fuel injectors.

The truck can barely make it around the block due to stalling out under load. I've replaced the spark plugs and wires and verified they're all sparking (so ignition coil packs are fine), and I've replaced the fuel filter and determined that the fuel pump is fine. The next thing I want to try is replacing the fuel injectors.

I don't want the old gas to gum them up as soon as I get them in. Should I try to get the gasoline out of the tank before I put in new injectors? And if so, how do I do it and how do I deal with the old gas?

I would have a really hard time storing and getting rid of 16 gallons. I could burn the gas up by letting the truck idle for several hours, but that seems like a horrible thing to do.

  • Are you sure the cat converter isn't clogged? Before you go replacing parts not knowing what the issue is, I'd highly suggest you figure out the root cause of your problem. It's usually much cheaper to do it this way and you'll be more happy with the results. – Pᴀᴜʟsᴛᴇʀ2 Dec 26 '15 at 17:02
  • Are you sure several hours is enough to burn the gas? My understanding is that consumption at idle is around 0.7liters/hour, meaning you need 3.6 days to burn all the fuel. But for a truck engine, idle consumption may be larger, but I bet it still requires more than a day. – juhist Dec 26 '15 at 17:05
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    If you have a laser thermometer, you can check it easy. Run the engine until it's warmed up completely, the take the cat's temperature at the very front of the cat and the very rear of the cat (where the pipe and cat meet in both cases). The cat should be significantly warmer at the rear than at the front. To the tune of 150-200 degF. – Pᴀᴜʟsᴛᴇʀ2 Dec 26 '15 at 17:08
  • @Paulster2 remember we now have a question you can refer the OP to on how to test the cats – Zaid Dec 26 '15 at 21:05
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If the tank was full up (or nearly full) there isn't a lot of space for the fuel to absorb moisture. If you can draw some fuel out to see how it looks, I'd go with that. If the gasoline is a rich amber color, consider getting it drained. If it's still fairly clear (towards looking like water), then it is probably fine.

  • Ethanol is the big killer of gasoline as it attracts moisture. If the gas which was in the tank was all gasoline (IOW: without ethanol), it would probably last a lot longer in the tank. I've seen where gasoline vehicles which have been sitting for years have fired up on the old gas in the tank. The major thing there is the rust factor inside the tank. – Pᴀᴜʟsᴛᴇʀ2 Dec 26 '15 at 18:35
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    @JesseSielaff Fuel deterioration with age is a multifaceted problem and water absorption is an issue. Evaporation of its lighter constituents is a major factor. Fuel is composed of 20 major and many minor constituents; all with different rates of evaporation. After a time the fuel will be closer to diesel than gasoline. – Fred Wilson Dec 26 '15 at 19:24
  • @Paulster2 I prefer an exhaust back pressure test for restricted exhaust over the cat temp test. The cat temps test was designed to test conversion efficiency and there are better tests for efficiency than the "delta T" test. – Fred Wilson Dec 26 '15 at 19:33
  • @FredWilson - I agree, but most people won't be able to run that test. A no touch thermometer will give very accurate results and is accessible by most. – Pᴀᴜʟsᴛᴇʀ2 Dec 26 '15 at 23:10
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I'd get the tank drained and put in fresh petrol. Petrol does go stale, I've had it in less time but not a full tank so I was able to add more fuel to get going. Even a full tank will still be exposed to the air in the tank.

I'd imagine it'll be cheaper to drain the tank than get x number of new injectors. Depending on the age of the injectors, they can be cleaned if you suspect they are causing part of the problem.

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