Following the symptoms of power loss under acceleration accompanied by P2293 and P310B codes the dealership diagnosed the cam follower and replaced the HPFP, follower and cam. Luckily, I was 3000 miles inside of their extended warranty for the TSB.

Unfortunately, this didn’t cure my symptoms and so I changed the fuel filter.

This still didn’t fix the issues and so I ran some VCDS logs to get some fueling data during the power loss symptoms. This revealed that the LP fuel rail pressure was maintain fairly steady at around 5-6 bar but the HP fuel rail pressure was falling dramatically, sometimes into single figures (6.4bar) from its normal range around 100bar (see logs below). The green row is where I start to accelerate. The fuel figures in red are the HP fuel rail figures during the power loss.

I returned the car to the dealership for further diagnosis along with the VCDS logs. I was a little confused when they diagnosed a faulty LP fuel pump for what seemed a HP fuel issue. Unwilling to commit to their diagnosis and replacement costs of $950 I sourced and replaced the pump myself for a little over $200 (see my LP Fuel Pump Replacement DIY also posted here). I wasn’t too shocked when this failed to fix the issue.

So, where do I go from here? Is it possible that fueling is but the pressure sensor is intermittent? Would a low HP fuel pressure reading result in the ECU reducing power? Any other suggestions?

To recap:
P2293 codes
Limited (flat) power under hard acceleration
HPFP, cam and follower replaced
Fuel filter replaced
LP fuel pump replaced

 

I have nothing to add, but wanted to tag this for future responses. I have been getting P0089/P0310B lately. I also feel the acceleration is a bit flat. Had the fuel pressure customer service action performed as well as the LPFP replaced last December which fixed it for a while, but it's been back for the last month or two (had some personal stuff going on and couldn't attend to it). Indy shop that did the FP said it was the cam follower issue, but when I took it to the dealership to get that done, they said, "Nope, it's your LPFP (again)." They couldn't explain why it would be bad again so soon. I paid/forced them to pull the HPFP and take pics and the follower looks almost new, so that's definitely not the problem.

It's in the shop today to have the LPFP replaced again. They're taking care of it since the part seems to be faulty within 12k miles/12 months, but they tried to blame everything else first. I guess I'll know eventually if this fixed it--I'm just a little concerned it won't and the issue will keep cropping up. So, I definitely am interested in hearing your results.

Also, can you do that diagnosis with the free VCDS-Lite or do you have to have the full version? I have an eBay VagCom-USB cable and can get the Lite version of the software, but didn't know if that was useful at all. Also, did you replace the fuel filter along with the pump? Audi recommended that and I told the guys at the shop to do it at my expense for the filter.

 

This one is mystifying. Like you, I was tempted to pull the HPFP again just to check that it was installed correctly and that they'd not missed anything. I ran another set of diagnotic logs (I use VCDS Ver. 10.6 I believe) a couple of days ago and for the first 30 minutes on the highway I didn't notice any issues. Only when I came off the highway and booted it from a standing start did I notice the fuel cut. Looking at these new logs (which differ from the ones shown here in that the LPFP had by this time been replaced) the LPFP is not working quite so hard, peaking at around 80% but more often working in the 50%-60% range. The other thing I noticed was that when the HP fuel drops off under hard acceleration, the LP fuel pressure actually increases, i.e. it almost seems like the fuel can't get to the HP side causing an increase in pressure on the LP side. To me, this says that the HP side is almost certainly at fault. It does very much sound like the HP fuel regulator but this would have been changed with the HPFP a few weeks ago but the symptoms are the same both before and after the replacement.

I did have a theory that maybe the HP sensor was at fault and that the cut in power was due to the ECU reacting to a lower limit fuel pressure signal and backing things off rather than the issue being a physical shortage of fuel. Sometimes, the physical symptoms feel like an artificial limit has been introduced but there have been times when the car bucks like you might expect from intermittant fuel starvation.

I really don't want to go back to the dealership as they seem clueless and don't want to consider the logs I have generated.

 

Did your P2293 code ever get sorted? I'm having the identical issue. Had significant loss of power and CEL came on with a bunch of fault codes. Dealer then replaced cam follower, cam shaft, hpfp, prv valve, lpfp, low pressure fuel sensor. After a short time driving, the CEL came on but only the P2293 code came back. They then suggested replacing the fuel filter which I did and the P2293 code came back. Coincidentally this came on on my way to refuel and the tank was low. The dealer suggested that low fuel in the tank might be the cause as well but that seemed a bit absurd considering the tank required only 50litres to fill and it's a 65 litre tank. Anyway it's been a few days of driving without a CEL or fault code but I'm doubtful that will last. Given that my fault code says that it's sporadic, i wonder if it's possible that it's an electrical issue (faulty wiring harness at lpfp?). Anyway, if you could give a follow up as to what happened in your case that would be awesome!

 

In case betyouaint doesn't check back in, here's his thread over at vwaudiforum.co.uk. Looks like cleaning the cam position sensor ended up fixing it, but not before he threw nearly every fuel system part at it!

Power Loss & P2293 - Fuel Pressure Regulator Valve (N276): Mechanical Malfunction - Page 3

In my case, my second LPFP is going strong 18 months later although I went through a lengthy and eventually expensive EVAP problem that they may have caused by pinching one of the plastic lines.

 

Thanks for the response! I did see that thread but didn't make the connection that it was the same person.
I mentioned this to my dealer and they said they replaced the cps at the time of doing the cam shaft. I never saw any photos though so can't say 100% that it's true. The dealer said if the CEL comes back on in the next while, they will put in another new lpfp and I will ask them to do a thorough check of the fuel lines as well as the wiring harness. It would seem strange to me that it would be a kink or leak in the fuel lines though because the fuel pressures on both the high and low sides are within normal limits in the VCDS in both idle and WOT at this point? So that's why I'm thinking that if there's a poor electrical connection that fails occasionally with certain car movements then it would appear the low side pressure and pump fail sporadically. If that doesn't do it then I guess I'll have to take it to a different mechanic for another look. At this point I've totally lost confidence in the Audi dealership I've been dealing with....thanks again though!

 

Yep... the cam sensor seemed be be the cause. I didn't even replace mine in the end. I just cleaned the gunk and fine metal particles from it. Think it's been over a year now without any problems, which for me is over 20,000 miles.

Only a 5 minute job to check it if you have the right sized torx.

Hope you get to the bottom of the problem without too much stress.

 

if you are tuned stage 2 or above you need an upgrade for the HPFP, it will fix your problem at 100%! Then you should upgrade for bigger injectors