I stumbled upon this TDI Dummy Injector yesterday. Nice photo, but without any explanation of what the purpose of a "dummy injector" is, let alone why one would spend nearly $400 US to be in possession of said item. Right now, I'm feeling like the dummy…

Dummy injector for VW ALH engine

  • It's weird. There's a TDI forum where a user says that Bosch p/n 0432193696 is the p/n on their actual injectors. And the Bosch auto site lists it only as "Nozzle and holder assembly (2-spring)" with no image or description.
    – Jason C
    Commented Aug 25, 2016 at 14:57
  • I'm betting it's just a placeholder item on the website that's not made to actually be ordered. It's a WordPress website, so not super-professional to start with...
    – JPhi1618
    Commented Aug 25, 2016 at 17:14

2 Answers 2


Diesel engines have very high compression. Using a standard compression tester, commonly used for a gasoline engine, will not work.

I am not sure about the item you linked to, but most all diesel compression test kits include "dummy injectors". The "dummy injector" is installed in place of the injector, torqued into place, and the engine cranked to get an accurate compression reading.

Also, the injectors which used pressure of the fuel to operate by overcoming a given spring pressure in the injector itself were called "dummy" injectors. Most modern injectors are electronic controlled (smart). Source

  • So it's a standard interface to the pressure gauge?
    – dlu
    Commented Aug 25, 2016 at 20:04
  • Yes, or it could be type if injector as stated in the additional info I edited into my answer.
    – CharlieRB
    Commented Aug 25, 2016 at 20:09
  • Wouldn't that be a dumb (as opposed to dummy) injector?
    – dlu
    Commented Aug 25, 2016 at 21:37
  • Maybe if we were discussing grammar, but that is what they were called. See source link, "Principle" section, third bullet point.
    – CharlieRB
    Commented Aug 26, 2016 at 11:59
  • I think the referenced post might be in (grammatical) error. I tried searching on "dummy injector" (with quotes) and pretty much everything that showed up within the first few pages on Google was for either compression testing or swarf (new word to me) removal. Searching for "dumb injector" found quite a few insults, but also references to "not-smart" injectors.
    – dlu
    Commented Aug 26, 2016 at 19:52

I know dummy injectors with a plug for pressurized air. They get used when drilling glow plugs or repairing glow plug seats, putting the combustion chamber under pressure to prevent metal shavings falling into it.

I am just speculating: Those expensive ones could have an integrated pressure sensor for a compression test?

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