haggisuk

Ok so fuse the wasn't blown but do you have 12v at the terminal of the fuse and if there is do you have 12v at the connector for the Maf

the reason I ask is that fuse is responsible for everything that has fault on your engine ecu

MP4.2+6.0

Yep, among the reasons I flagged it too. No codes, so need old school diagnostics which to me sounded like fuel starvation. From some posts of late, it does feel some like various professionals in the biz. (dealers included) are maybe forgetting on FSI models there is still the low pressure pump set up in the tank to move the fuel forward.

Also for OP, are you sure your battery is up to snuff? Suggest making sure it is charged up fully, disconnecting (which can sometimes clear weird code issues), and clearing all modules. Clear module by module if you aren't already--the VCDS clear all command does not work as you might think it does. Then if it doesn't resolve, a bunch of the short to ground ones can't easily be explained except by wiring issues or problem with ECU itself. But before getting there, I would want to be sure the data itself is reliable--hence battery focus, systematic code clearing and so on.

jbrannam

Battery was just replaced & is reading 14+ volts. Will start checking fuel system & MAF more closely. Original research of symptoms had me leaning toward fuel pumps til we found HPFP leaking. But of course that was too easy haha

MP4.2+6.0

Still, do full battery disconnect (30 min) and module by module code clear for any with codes to be sure scan data is reliable. Then see what you have.

jbrannam

Gotcha. I did clear codes in the engine module as opposed to in the autoscan. Not sure if any of the codes affect another module. Will take a look

Sirjoznyj

Can you explain where was the problem? In fuel tank? Fuel pump? Or after the hood?

jbrannam

Haven't been able to get to in depth testing yet - that's on tap for tomorrow. I did clear codes module by module and the same ones came back again. Quick question though - is it normal for the car to stall almost immediately if I remove the oil filler cap?

MP4.2+6.0

No to your question, not normal. Be careful too--suggests to me maybe some kind of big vacuum leak or pull though oil galleries, which can damage key engine seals and turn into a nightmare. As in, best not to drive without figuring that out. Look in particular at oil vapor system for functioning. For a port 4.2 that would be the older style PCV valve; for FSI it is perhaps a fine oil separator set up. I don't know 4.2FSI at that level of detail though.

haggisuk

I have to disagree with you on this, removing the oil filler cap will indeed cause the engine to stumble or nearly stall as there is now a high volume of unmetered air allowed into the intake.

MP4.2+6.0

Fine, but doesn't sound right to me in turn and not my own experience. If anything I find on most motors they are slightly pressurized at idle, not pulling vacuum. You pull vacuum from an intake, not a crankcase, and traditionally PCV valve helps deal with unregulated vacuum pull while burning off oil vapors. Pre PCV valves--that were first basic smog device in 60's--crankcase was vented to atmosphere and not even ties to intake; definitely had nothing to do with vacuum pull. Haven't had reason to check any of mine recently though.