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Hey all. It's been about a decade since regularly posting here with my 2004 A8. I've got a new to me (now classic) S8 I've been completely rebuilding and I've got an issue that has me somewhat perplexed. Almost immediately after a full top end service (carbon cleaning, coils, spark plugs, gaskets, etc) the car started spitting out a P2293 and P0087 codes. So here's what we're looking at:
Symptoms: Over the course of about 200 miles the vehicle at first started throwing the P0087 code, then the P2293 code. Initially no drivability issues but then it started going into limp mode. Even when it went into limp mode, it didn't feel like there were any drivability issues. I put a full tank of gas in the car and drove it 100 miles from one of my homes to the other and over that 100 miles there were no codes thrown and there was a lot of hard acceleration with no drivability issues. I proceeded to drive the car for another couple days with no issues and then boom: hard stuttering under anything past half throttle and instant engagement of EPC/ limp mode. It now does this every time.
Codes:
P2293 - Fuel pressure regulator 2 - Implausible signal
P0087 - Low fuel rail pressure
Diagnosis: Scanning shows that commanded pressure does not match actual pressure. And application of throttle results in an initial raise in fuel rail pressure from about 400psi to about 750 - 800psi but that rise almost immediately drops to 140 - 250psi. So basically my fuel rail pressure is dropping in half when I give the car throttle. I don't suspect a stuck fuel injector as the car sat for weeks on a battery tender and fired right up. I swapped high pressure pumps to see if the problem followed the pump or stayed on the same side and the codes return on the same side. Here's my issue though... The P2293 code seems to suggest the driver's side pump however I'm not sure if that code truly pertains to a side because I don't see people posting any codes for fuel pressure regulator 1. I also don't ever see people telling others to swap the pumps from side to side to see if the problem tracks the pump or stays on the same side. So that tells me that code probably isn't really identifying which pump is throwing the error.
I'm really just trying to determine whether I have a low pressure or high pressure issue. The pumps for the S8 are absurdly expensive and while I don't mind replacing them, I don't want to find myself in a position where I've paid $1000 for fuel pumps only to discover a low side pump has failed. I know this forum is mostly A8 owners but as the FSI 4.2 is basically identical to the 5.2, I'm hoping someone can give me some insight. Thanks in advance!
Fwiw I had a similar problem, either clogged injector, pump or fuel line. The fix was liquimoly fuel system cleaner, ran the car 2k rpms for 15 minutes, it cleared up the clog. Not saying this will work for you but it did for me. You may have introduced some foreign material when you did your intake and had the fuel lines open.
The HPFP’s work in tandem, not per bank. Both pumps feed the same common fuel rail, serving all 10 cylinders simultaneously.
The regulator 2 implausible signal error suggests an electrical problem with HPFP 2, causing it to operate incorrectly and the subsequent low fuel rail pressure error.
As you’ve physically swapped the pumps around and the error didn’t move with them strongly suggests a wiring fault for HPFP 2. Maybe you damaged some wiring or a connector during your recent work? Is the connector seating properly on the fuel pump?
Take a look at SSP 376 for the V10 engine. Tons of great info and diagrams on how it works, with the fuel system detailed on p22-25.
Thanks Dave. It did end up being the high pressure pumps.
The thing I still don’t understand is that there doesn’t seem to be a corresponding fuel pressure regulator 1 code to the fuel pressure regulator 2 code (p2293).
For that reason, rather than pointing to the drivers side pump, I’m assuming that’s just the standard “fuel pressure is different than expected/ commanded” error because it seems that’s typically the code people get when a high pressure pump fails, regardless of which one.
Ok. Usually the DTC is accompanied by a component ID in parentheses, specifically ID’ing which sensor/device is the source of the fault code. The DTC’s you posted didn’t show any additional info, hence my assumption you weren’t using VCDS. It’s important to post the entirety of a fault code as it contains lots of other diagnostic information than just the DTC itself.
Do you still have the full VCDS scan? Copying and pasting that in full should show which component was generating the fault. eg (G247)
02-06-2022, 07:58 AM
S8 fuel issues
