Lumpy start

**karlkane** · 01-09-2024,04:00 PM

Hi,
in a spot of bother that is driving me mad. I have a 2012 C7 A6 2.0 tdi 177bhp. Drives very well, great acceleration, smooth acceleration, and no error codes generated. My problem is this...when I go to start it, it is very lumpy and struggles to catch. Sometimes it stops turning, the glow plug flashes for a few seconds and then tries again. After I switch of and try again it evenstarts, and 20 seconds later it idles smoothly. I was informed the pressure regulator could be leaking back, so I replaced it, no such luck. I have checked the injector values and they are in spec. The only anomaly I have I'd the fuel pressure control deviation value...it oscillates from a minus 2000/4000/6000 to a positive high value in the thousands. Does anyone know where this value is derived from, is it taken from the fuel pressure sensor on the fuel rail? I think I will change that next (it's cheap enough) bit if anyone knows if this is to be adapted please advise. And if anyone has any ideas as to what else it could be it would be great!

**Crasher** · 01-09-2024,04:03 PM

What is the VIN and what fault codes are stored?

**karlkane** · 01-09-2024,04:32 PM

The VIN is WAUZZZ4G7DNO35486 and engine code CGLC176644 and that's the thing, no error codes at all.

**karlkane** · 02-09-2024,05:52 PM

I am going to gey another fuel pressure sensor and see what happens, but if you have any ideas it would be great

**Crasher** · 03-09-2024,01:27 PM

WAUZZZ4G7DN035486

You aren't using VCDS are you? If the glow plug light flashes, a code has to be stored. There are a number of TPI's that could match the symptoms IF there really are codes stored.

**karlkane** · 03-09-2024,10:33 PM

Yep, I have a legit VCDS, and no, no codes stored at all. Except 1...but that was because the starter stopped turning as it was so lumpy it felt like one cylinder only was firing. But defo nowt wrong with starter. I did check the egr and thats fine (except for vacuum operated cooler bypass was stuck). It's a real conundrum without the a code being generated.

**Crasher** · 04-09-2024,05:10 PM

That doesn't make any sense if the glow plug light came on.

**karlkane** · 04-09-2024,07:46 PM

Bloody exactly!!! I just don't get it. I got a pressure sensor today, gonna fit it and see if it helps. Does it have to be adapted do you know?

**mickeybo** · 04-09-2024,08:17 PM

The glow plug relay gets its input from the temp sensor witch it uses to adjust the duration of glow plug pre heat cycle depending on engines temperature longer when cold shorter (or not at all) when its warm ( or hot)

**karlkane** · 10-09-2024,07:34 PM

Yeah, I get that, but it's not a glow plug issue. I have physically checked them, and they are OK. It's like it's fuel starved and hiccups when trying to start. 20 secs into it and it's fine...drives very well, pulls like a train. I'm at at a loss.