2006 A4 2.0T - Car died at red light, won't start. Tried many things, any ideas?

[TheMixer]

Hey all, appreciate any help in advance. Here's the short version:

- Engine died suddenly at red light. Wouldn't start. Had it towed back to my house.
- Before, I had some MILD rough idle issues when cold, but nothing serious enough to indicate any serious demise incoming. No stalls or anything before suddenly completely dying.
- Did the easiest thing first: replaced the battery (it was old anyway). It turns over, but still won't start.

So, I ran VAG and got a bunch of fuel pressure codes: P1093, p2187, p310B, and p1602

I know one of these points big at the cam follower, and I hadn't checked it in a while, so I did. And, of course, thing was destroyed (and it also destroyed the little spring piston thing on the high pressure fuel pump, wore it down a bit and broke the spring).

I bought a new cam follower and a new HPFP, and earlier today I installed them both. Still wouldn't start. So, for my last effort, I also installed a new fuel filter for good measure (really not sure how old it was).

Damn thing still won't start. Still tries to turn over, but engine won't start. But all the fuel pressure codes are gone, and it won't throw any codes at all after trying several times to start the car.

So, from what I can see, I fixed the issue, there are no vag codes, but the damn thing still won't start. I'm at a complete loss here.

Two things to note:

- When priming, the high pressure fuel pump makes a high pitched whine. This may or may not be normal, but I never noticed it on the old one. I'm slightly worried I installed something wrong, but I'm 99% sure I didn't (and I've checked for any gas leaking or anything when priming, and there is nothing). I guess the new HPFP could be defective, but it was brand new and... I hope not.
- After priming/trying to start the car a few times, I've tried pushing that little release on the high pressure fuel pump to release fuel pressure, but absolutely no gas comes out. Again, this might be normal since the car never actually started, but I'm not sure (is no gas reaching the HPFP?).

Only other thing I can think is maybe the low pressure fuel pump in the tank? But it would be a weird coincidence for it to die at the same time as the cam follower/HPFP, and there are no fuel pressure codes anymore.

Or perhaps when the follower/HPFP failed, it damaged the cam itself? It doesn't look bad visually (from what I can see), and I don't think a little wear would completely prevent the engine from starting (just make it run like crap), but I guess it's possible...

Without any VAG codes, I'm at a complete loss here. Any ideas? Thanks a billion for literally any ideas here. I don't even know what to try next.

[Older_not_Wiser]

If you have VCDS try logging low side and high side fuel pressure. That may provide some info to give you a direction for further investigation.

No fuel out of the HPFP relief valve may point to LPFP or a clog or a wiped cam.

[TheMixer]

If you have VCDS try logging low side and high side fuel pressure. That may provide some info to give you a direction for further investigation.

No fuel out of the HPFP relief valve may point to LPFP or a clog or a wiped cam.

Good idea, hadn't thought of that. Will do in the morning.

Any specific values I should be looking for in the low side and high side?

[Older_not_Wiser]

Well, not really sure what to expect of low side and high side fuel pressure while cranking and not starting, but there should be pressure for both.
Maybe 3 - 5 bar on low side as LPFP is electric and should make that if it is functioning. As for high side, look for at least 50 bar? During a pull requested is 110 bar, not sure i ever looked at requested at low load, much less while cranking.
Let us know what you find.