2003 Audi A4 B6 Cabriolet 1.8T Sport fuel pump troubles

[Felix_DM]

Hi all,

My first thread here. I recently had a breakdown with the Cabrio at 91K whilst in town. Parked up in mall parking lot and went about my business. Coming back to the car I got in and turned the ignition. The engine turned on, sputtered a bit, then died. I managed to turn it on a couple of times more but it died on me after about 5 seconds each time, sounding like it had been starved of fuel. We got evacuated back home and I started looking into the issue.

A bit of prologue to the story: now and then, when I would start the car it would make a groaning sound in the back. I hadn't taken notice of this as the groaning would stop a few seconds after the engine was on.

After the breakdown, I naturally started looking into the issue and found a video of the sound a fuel pump makes when the fuel filter is clogged up and it was spot on. Here's the video: B6 A4 Audi 1.8t Fuel Pump - YouTube With me the nose was a lot louder though and would like I said die off soon after the engine was on.

My engine trouble codes also had one pending code "Lean mix, bank 2" which to me seemed to support the hypothesis (read via a WiFi OBDII interface on my phone). I bought a new filter and changed it that weekend. There was some muck that came out with the fuel, which again solidified me in my opinion that it was the filter. I had been hoping that was the end of it, but alas, the car would still not start. Cambelt is intact, thank god for that. Next things to check: fuses, relay and fuel pump.

The fuses are fine, number 28 is intact - this is the fuse that i've read is connected to the fuel pump.

The relay (number 167 on this model, correct me if I'm wrong) looks and seems to be working fine, although I hadn't checked it under battery current.

Today I decided to check the fuel pump. Once I got to the connector I turned the key to ON and checked the voltage across the thick brown (ground) and green/yellow (+) connector slots and got a pretty weird reading - a +- consistent 18.4V. Is this normal? The battery had been charged fully the day before. Also I checked the resistance across the same pins on the pump itself and got a 1M Ohm rising to beyond the multimeter's range within about 2-3 seconds. This happens every time I measure the resistance. As far as I know car batteries supply 12V, so I'm at a bit of a loss here. Also, does the megaresistance of the fuel pump mean that it's trashed? What is the resistance of an intact fuel pump across its contacts?

Looking forward to your thoughts and tips on this. )

[Felix_DM]

So I got my tools and parts together:

checked the relay - OK
checked the fuel pump - replaced, since the old one died (tested it before replacement with an 18V Battery - for anyone who's in a similar situation, these pumps run on 18V, not 12V, so if you're checking it try connecting to a cordless drill powerpack (18V of course) instead of the car battery)

Now I have a new issue that has me puzzled - the car will not start from cold when I crank it the first time, however, 2nd cranking (turn ignition off, turn back right away) time it starts from a half-cycle. Has anyone encountered anything similar before? The fuel pump gives a healthy noise working noise when turning the key to on, so it's not that. Otherwise the cab is running perfectly and after the whole debacle, I'm confident in taking a go at replacing the engine mounts over the weekend.