Answer
Aug 13, 2025 - 03:58 AM
On most Audis, a failing fuel pressure regulator can cause a mix of running issues and fuel smell. Common symptoms include:
- Hard starting – especially after the car’s been sitting (excess fuel leaking into the intake).
- Rough idle or stalling – unstable fuel pressure can cause the mixture to swing rich or lean.
- Black smoke from exhaust – regulator stuck closed can lead to overly rich running.
- Fuel smell – if the diaphragm is ruptured, fuel can leak into the vacuum line and into the intake manifold.
- Poor fuel economy – engine runs richer than it should.
- Check engine light – codes for rich/lean mixture, misfire, or fuel pressure out of spec.
A quick check on older vacuum-controlled regulators is to pull the vacuum hose — if you see or smell fuel in that line, the diaphragm’s shot. On newer returnless systems, you’d confirm with a fuel pressure test comparing readings to spec at idle and under load.
Of course, the fuel pressure check procedure is covered in the service manual, along with step-by-step instructions, clear images, and exploded-view illustrations. The manual is your best bet for solving issues like these.
If you could let us know which Audi you're working on, we'd be more than happy to direct you to the right one ✌🏻
