Car is a Audi S5 2008, direct injection, 8 cyl.

I will be removing the intake manifold to clean the intake ports of carbon. In the process, the fuel rail needs to be removed. The injectors aren't screwed down, so some may be stuck and come out of the intake port, while others will only be removed from the fuel rail.

The seals only come as a kit (pieces 5,6,7,9 of the diagram), and are quite pricey. Should I replace all the seals, even if they're not damaged? Will I be asking for trouble (fuel/vacuum leaks, performance issues) by re-using the same seals?


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1 Answer 1


tl dr: Replace the old o-rings

I would suggest you don't have to replace them, but I would replace them anyway. If they are the original ones, they are probably around 9 years old. At this point, the rubber is probably very hard. Secondly, you've probably already nicked a couple of them, which means they'll leak unmetered air into the intake system. This would be VERY hard to account for and even harder to find, which will make your engine run poorly. You will not regret replacing with new. You may regret not.

It looks from the diagram these are the typical o-rings used on most modern day fuel injectors. Finding the correct o-rings should not be an issue, as most any parts store is going to carry them.

  • Are you referring to the upper o-ring (#6) only, or both that and the lower seal? The lower seal (#9) is a Telfon seal.
    – tgun926
    Commented Nov 5, 2016 at 21:01
  • I was speaking in general terms for the rubber o-ring, so just #6 if #9 is teflon. I don't think you can easily replace the teflon seals. Commented Nov 5, 2016 at 21:56
  • Teflon seals are easily replaced. To install, you need to soften them by soaking them in hot water (not boiling, but steaming - like hot coffee temperature) then you can install them just as you would any other o-ring. I personally prefer a thimble type tool over a pick for these, but you could use either successfully. Once installed, they will be loose from stretching to install. To get them to shrink back to normal size, you just place the assembly back in the hot water and they'll shrink right back to normal.
    – CBRF23
    Commented Nov 6, 2016 at 0:38
  • @CBRF23 are you saying after you install the seal to "dip" the tip of the injector in hot water and the teflon seal will shrink?
    – tgun926
    Commented Nov 6, 2016 at 20:53
  • Yes. Exactly. And if it doesn't shrink completely up you just push the thimble over it to squeeze it into the gland. I forgot to mention that, but that's a good tip too.
    – CBRF23
    Commented Nov 6, 2016 at 21:10

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