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

[betyouaint]

Okay... so yesterday I changed the HP fuel sensor for this replacement...

Audi > A4/S4 > B7 A4 > Engine Performance > 2.0T > Fuel System

The replacement item was shorter than the original which seemed a little odd but it was the one listed for my car.

Car seemed okay for the first couple of miles but then when I really booted it, the problems returned worse than ever. Now I get the same engine code only now it puts the CEL on. In running VCDS (see log snippet below with added fuel pressure delta column), the HP fuel sensor reports no more than 90 bar (actual) on the HP fuel rail despite the specified being around 110 bar. For the range 0 - 90 bar, the actual value matches specified value pretty closely but beyond 90, the sensor stalls at 90 bar. The car has almost no power and 0-60 comes up in around 30-40 seconds. Not really much fun for my 80 miles round trip commute.

Now, either the new sensor won't read above 90 bar (even though it seemed fine for the first couple of miles), or alternatively, whatever was causing the original intermittent drop in fuel pressure has started to fail more consistently, quite possibly the fuel regulator valve, as a result of my vigorous test driving. I already have on order and hope to receive it in the next couple of days.

Tomorrow, I plan to switch the HP fuel pressure sensor back to the original and see if that gives me readings over 90 bar. As you can see from the original logs, the readings with this sensor showed readings up above 90 bar and were pretty consistent with the specified values until the intermittent power loss when the specified was over 100 bar and the actual could drop as low as 6.4 bar. I'm hoping that once reinstalled the original sensor mirrors the behavior of the new one, confirming that this is not a sensor issue and is more than likely a failing pressure regulator valve.

I've also notice that the LP side is hitting high 6's which I'm wondering if has something to do with the influx of high pressure fuel from the HP rail to the LP rail via the pressure regulating valve. Just a theory but it kind of fits...? Of course, it could just be the LP pump responding to the HP fuel situation by ensuring it is delivering enough fuel.

[betyouaint]

This morning, I replaced the new sensor with the original and the symptoms are now back to pre-new sensor. New logs (below) show the original sensor reads (or seems to read) 120+ bar and the car seems much happier than with the new sensor. Wrong replacement sensor I guess? It doesn't look the same and none of the numbers match.


From earlier logs containing lambda information during low HP fuel readings I have no solid grounds for suspecting that the HP pressure sensor be at fault as fueling seems okay for the the most part. This I believe confirms that the replacement sensor is definately the wrong item and tops out at 90 bar.


Never easy to be certain as the engine management corrects for out of tolerance conditions effectively masking the symptoms that might help in diagnosis.


The other thing I'm noticing is that the HP rail fuel pressure is exceeding its specified value just before the symptoms occur, e.g. specified of 109 bar, actual of 126 bar. The specified and actual track pretty well throughout the range, usually within 1 bar. Only around the time the problem occurs do they part ways and the control loop starts to fail. I'd be interested to see logs from a healthy car comparing these values under high acceleration.

[betyouaint]

OK... I've been mulling this one over a bit more. Something that A8Tech was talking about regarding a blockage in the PRV got me thinking. I noticed that in most cases, when the power loss occurs when the actual HP fuel pressure exceeds the specified pressure. I also read something that when people have tried to fit an uprated PRV to a standard tune they have had issues. It was suggested that this was because the tune detects the over-pressure and backs everything off. In my case, I have a standard PRV but if it is blocked or not opening at the designated pressure then it's possible that the engine management is backing off due to the same over-pressure scenario.

I have a new PRV in hand and will hopefully get around to changing it out this weekend. I'll let you know...

[betyouaint]

PRV changed this morning with the help of my 9 year old daughter (still in her footie pajamas) and her tiny hands (see below). I did a quick test run (with logs) and all seems good but I'd like to run a longer test to be sure.


Looking back at the logs, the actual and specified values tracked really well and the actual rarely went over 110 bar. There was one instance where it hit 126 bar for a single frame but that was off throttle and so I didn't notice any power loss symptoms. At no time was the actual significantly lower than the specified with the maximum negative delta being -3.2 bar for a single frame.

In your case, I think that you’re on the right track with the PRV, but I think that your logic for why is wrong.


I doubt that the ECU is deciding that the rail pressure is too high and then backing everything off. The reason I think this is that if the PRV remained shut the actual rail pressure would stay high and not drop like you're seeing.


My thinking is that we both have a lazy PRV that doesn’t instantly re-close when the pressure drops back to lower than its “crack” setting.

Yeah, my initial thinking was that the PRV was lazy on both opening and on closing and this may indeed be the case. It was the post (see PRV change DIY in tech forum) that got me thinking about the ECU backing things off. There's no doubt that at times the symptoms I've experienced have resulted in the car going into limp mode and have not simply been due to fuel starvation. In the case of this ECU back-off theory, my thinking is that the drop in fuel pressure is a combination of the ECU regulating the pressure with the electrically actuated fuel pressure regulating valve in the HPFP and the natural consumption of the engine which is still taking it from the HP fuel rail and firing it through the injectors into the cylinders. I have no idea if this really makes sense (without knowledge of the control loops in the program itself) or even if the fuel usage would allow an almost instantaneous reduction in pressure from 126bar down to 6.4bar?


On the plus side, either theory suggests that the PRV is at fault.


I'll report back after a longer test run...

[betyouaint]

I went for a longer test drive last night and did manage to produce a couple of small hiccups during a dozen or more high throttle runs. Nowhere near as bad as it was but there's still definitely something amiss. I didn't run logs and I haven't checked for codes but there is no CEL on. Also worth noting, it was very cold last night, well below freezing, which may have a bearing on the issue a previously discussed.


I'll try again tomorrow and run some logs.

[Burt Macklin]

Subscribed. Very eager to hear your resolution. I am having the same issue. A side note on some of my issue's background. I took my 2011 Tiguan in for a NHTSA safety recall in reference to air bubbles in the fuel line, or something silly like that. The "fix" was increasing the fuel pressure to somehow prevent bubbles from occurring. About a week after that service was done I encounter the same loss in power and P2293. Only symptoms are check engine code P2293 and loss of power. It feels as if there is no boost. Otherwise the vehicle has no drivability issues nor observed changes in MPG. Please keep me updated!

[betyouaint]

Still no resolution...


Longer tests runs saw the return of the original symptoms and I've posted a bunch of logs below. The green highlights show where I was above 70% throttle, the red shows where actual HP fuel pressure was significantly lower than specified HP fuel pressure and . Pink shows where actual exceeds specified.


I've tried 3 different HP fuel pressure sensors, the original, a replacement that was the wrong PN and only gave a maximum reading of 90 bar, and a used part from ebay, which was the same as the original. I doubt this is the culprit but have a new one of the correct PN on its way.


I have also ordered a LP fuel pressure sensor (thrust sensor) which is the last thing on my list. After that, it's back to the drawing board.

[betyouaint]

And for Burt... here are the pictures of the mechanical PRV I changed, which is different from the electro-mechanical pressure control valve within the HPFP.

[betyouaint]

G410 thrust sensor (LP fuel sensor) replaced. Symptoms still apparent.


A brand new HP fuel sensor (correct PN) arrived yesterday. I'll be fitting later today but not sure when I'll get chance for an extended test drive.

[CupraDave]

Hey buddy, I have had a similar problem with my Seat Cupra K1 I think it's going to be pretty much the same car running standard 240bhp, Loss of power when I put the foot down, took it home got the same code as you, checked the HPFP and it had a crack in it, replaced the HPFP but now the car won't start at all, you had any joy with any of the other parts you changed? I've been trying to sort this since the 1st of December, absolute nightmare! Not handy either when I just forked out 260 quid for a part that hasn't resolved the issue.. I have taken out the coil packs and spark plugs to see if there was anything indicated there that wouldn't be starting the car but everything seems fine, getting to the end of the road where this is going to turn into a bonus round of Street Fighter! Haha, hope your car is back running again mate, any advice would be great, cheers.