Occasionally have to "tap" ecu box to start

[rtk8892]

My b6 s4 6 speed has this weird issue, where sometimes when I get in and then the key I don't hear the fuel pump prime, when this happens it will turn over but will not start. If I pop the hood, and "tap" or hit the black ecu box a few times then try again it will always fire right up.. I am getting power train data bus codes with vagcom and eeprom error codes as well not sure if they're related to this issue. Just wondering if anyone's dealt with this and might know the cause

[emilio]

definitely give us the extra codes. how hard do you have to tap? a "good dog" pat, or an "anybody home" knock?

most of the ECU connectors are pretty secure, so it would take some serious bump or corrosion to disturb them. however, there are relays and fuses in the ECU box that could be loose or failing. there is one relay right under the ECU itself that runs the computer and a few other things, so maybe that is specifically getting flaky.

there is also the fuel pump relay (which runs WAY more than just the fuel pump), but that is behind the main fuse panel and not in the ECU box.

- emilio

[Lucca M]

Is it manual or auto? Check the 414 relay. It might be going bad and car wont start

[TarlCabot]

sounds like a wire harness connection issue... possibly decay or fragile/broken connectors....