Deezell

Just to close this thread, fuel pressure regulator valve checked out. I found a lad who was willing to take it on, but ended up baffled for a while. He removed injectors, seals were fine. Had them tested all were OK, off a little so got them serviced and calibrated. No metal anywhere, so no indication of failed HPFP. He stripped the top to get to the pump anyway, and removed the solenoid low pressure inlet valve. If this fails car should run in limp mode. Lo and behold it was not actuating, though solenoid resistance was good and impulse present. He had difficulty finding the part number, as Audi will only supply the entire HPFP if this fails. I had the number from the 7zap parts diagram website. Its a Bosch valve and not too expensive. The guys who serviced the injectors had one, so once installed, the car started. Plenty of work, I shudder to think what a main dealer would charge for the HPFP, and the complex work to change it (turbo out, DPF out ). I don't mind the injector servicing, they're all matched up now and in spec. The whole lot cost €840, so I'm happy out. The original consensus of injector failure was incorrect, not helped by the Audi training manual asserting that a failed solenoid valve on the HPFP would not prevent starting, even in limp mode. My man was baffled by this also, but the solenoid seems to have failed in such a way as to have closed the input to the HPFP chamber completely. It's a pity it's so inaccessible also, just a little less clutter and it could be removed and tested early in the game. Not being an official spare part is also strange, perhaps Audi feel that any failure in the pump warrants it's entire replacement, due to the high labour of just getting in there. I hope this helps someone, as the original poster also found it a maze of possible faults. Not helped by no recorded faults due to the purely mechanical nature of the stuck actuator on the solenoid. Thanks to Jason for all his suggestions, though his contributions have mostly been removed except where I quoted him. This is the only critical fault this car has had in my 6 years of ownership, and at 245,000 km, so I'm not complaining.

Here it is idling normally, fuel high pressure almost exactly on the requested 250,000 Hpa. Warm start Normal idle.mp4

Heres a video of rough idle data before it sat down, fuel high pressure swinging wildly. Cold start Rough Idle.mp4

1.a As I understand it, the copper seal is the culprit. It's there to contain hot gases from whizzing past the Injector body and heating/cracking the casing. 1. Injector part no is 059130277CR. The Bosch equivalent is 0 986 435 441. The Bosch 0 986 435 360 is flagged as not suitable for my car. 1 b. Yes, it has a solenoid, but this solenoid force doesn't directly meter the injected fuel, rather it creates a differential pressure on the needle valve piston which then opens using the fuel pressure against spring pressure and injects the fuel. The solenoid thus only needs low energy to active a hydraulically actuated needle valve, rather than acitvating the valve itself. Clever, I recall studying a similar system for pneumatics in college way back in '73, known as a flapper/nozzle. Tiny forces controlling larger pressures. I'm rambling, as one does All this is indeed relevant, I'd put the absence of fault codes down the fact that once started, it worked, but is not showing in engine data on non start. How much exactly can the ECU know about what is happening in a particular cylinder and injector, there are no sensors in the actual injector afaik. Some starts had brief rough idle, misfiring, but cleared without leaving an error code. My car is early 2015, I bought it 2018 but is the face-lift, as it has the clean engine tech, with combined SCR/DPF, and it had the new MIB2+ multimedia software version, which a few years ago allowed me to install Android auto/Carplay on it with a free script some genius put up on the Internet. Sadly, I was about to trade in when it sat down. I'm picking up the new (used) car Saturday anyway, so I'll have to get this one fixed to sell it on. I already have another old 5 series lying up, I've just solved a haywire control unit issue on it after years, WYB water in the reverse sensor control unit. it has to go too (she says).

That 0.01 is with the engine stationary. Play the video to see cam and crankshaft speeds, the latter twice the former. Sensors are definitely reading. The static 7900Hpa pressure in the rail is odd, it rarely changes. Perhaps sensori calibration way off, or its not accurate at non operational low pressures. I'm really beginning to think there's a leak in an injector. I spoke to another mech near me who suggested an injector stuck open, he said this would drain the pressure sufficiently to prevent any injector functioning. He's agreed to take it on in his shop. Here's hoping he spots something. I'd say I have a compromised injector, overheated by a bad seal, whose ticking I've ignored. Actually, the main dealers who sold me the car in 2018 noticed it on the first service I put it in for in order to keep the 2 year warranty I'd gotten off them. Its on the service invoice, and marked 'requires further investigation'. Did they not know what that sound was? I didn't, and they never investigated further. instinct will always make you think ticking valves and tappets from engines of old. Since then I've learned that a leaking injector seal can make just that sound, and the ignition gasses escaping past the outside of the injector casing will stress heat it and damage it. This could easily cause the internal injector valve, which is opened not by a solenoid but by fuel pressure itself, to hesitate before closing, or stay stuck open on the next engine start. Its the same second opinion of the probable cause I've been given, so I'll let him at it. I'd be really happy if the HPFP is intact, thats a 4 figure repair.

az_recorder_20240214_135842.mp4 Crankshaft and Camshaft sensors reading. I loosened an injector pipe nut and pushed the pipe a little to relieve pressure. I don't think there's anything there. Sensor remains at 7900Hpa. I might need to loosen both ends to withdraw the injector pipe, I was pushing it back about 2mm, no leak or dribble of fuel. Surely 7900Hpa would have pushed out past.

I'll take a look at cam sensor data also, it should be active on cranking.

1.- 4. During Normal idle, rail pressure is 250,000 Hpa, with little variance. This is 250 Bar, 3600psi. Its nowhere near high enough at cranking, which is static at 7900Hpa with the ignition on. Doesn't change with cranking, though sometimes it will jump to 10800. Either the HPFP has suddenly failed, the metering valve on the pump is stuck closed, the pressure valve is stuck open, or there is a massive breach in an injector to the fuel return. No fuel left the temporarily disconnected fuel pressure regulator return tube on cranking. It is closed as it should be to raise pressure. It should open at engine off, to relieve vaporisation in the rail. I suspect this valve also, and I might just remove it to inspect, though I've read its a once off device, remove and replace with new. I'll just have to loosen a nut on the fuel rail Relieve the 114psi pressure, which is only what you'd find in a skinny bike tyre, so safe enough. I'll crank momentarily and see if the HPFP is driving fuel into the rail. If not, then it's the HPFP or its metering valve are at fault. 5. No obd faults whatsoever. I'm assuming static conditions are met, and the engine await fuel pressure rise and start. It may be storing failed start incidents, but may have a counter in these before throwing a fault code.

It's a timing chain, camshaft adaptation angle under 3.5° last time I checked with a running engine, so chain stretch well below concern level.

1. Only as far as checking it's receiving voltage from the ECU at the FPRV Valve end. I'll have to check the ECU end for dry connectors internally. I'm aware that leaking valves, pumps and sensors have been the cause of some horrible ecu/tcu failures when coolant wicks up inside the cable looms to control unit connectors. I had one of those 'transmission coolant valve leak TSB' issues fixed under extended used warranty in 2020. Car was losing coolant, but no trace of where it was going. Audi main dealer replaced the transmission cooler valve under warranty, like it was a secret. Nothing recorded in the service history. I did have to top it up middle of last year, so that's a mild concern. 2. I wouldn't probe the ECU, but I'll check connectors for moisture. 3.a Yes, I drained the tank at the filter connection, primed using my. OBDeleven. Changed the filter. Opened the old one, no trace of metal from HPFP return, so I'm hoping high pressure pump is good as it ran perfectly until it was driven home and stopped. I'm hoping its not a water/coolant up the internal cable loom issue that trashed control units in these cars, most notably the TCU one from way back. 3.b No faults stored other than when I disconnected the fuel pressure regulator valve plug. The resistance of the valve solenoid seems very low at 4 ohm's, but its not flagging as a short circuit to the ECU. My meter is 10 M Ohm impedance, so no risk probing the connector pins carefully. It read 3v, which would be an average reading of a pulse modulated higher DC voltage. I have an oscilloscope if I need to look at the valve voltage waveform. That FPRV valve is normally open, to vent possible vaporisation in the fuel rail to the return when engine is off. If it fails and is stuck open, pressure can't build in the rail. Car won't start Conversely, if it's stuck closed, vaporisation can't vent according to vag self study manual for this engine, which I managed to find. Its possible it's an injector issue as advised by one expert opinion. I can see how that could be with combustion gas entering the injector chamber through a crack. I haven't removed the FPRV, fuel pressure regulator valve yet to check its action, some posts say it's a one off install, has to be replaced once unscrewed. Others differ. I did remove the return hose from the valve end of the fuel rail. It was dry, and no fuel was passed through it on cranking, so the valve is definitely not passing fuel through from the high pressure rail. Its my chief suspect, and I think the fuel rail has no fuel in it, just trapped gas/vapour, and its preventing high pressure build. I'll try find data for the solenoid resistance. How do you normally fill/bleed a common rail, by opening the furthest injector pipe nut? I've not had to meddle with diesel injectors since my farm machinery driving/fixing days in the 70s. I'll just have to get it towed when I can find a willing and able engine guy. They're all snowed under maintaining the increasinngly ageing used car population. Heres a useful page on the FPRV. Here's the VAG 3l tdi clean diesel self study guide which might benefit members. 840193_3_0_TDI.pdf

Yes, though I've discovered the sudden appearance of the flashing glowplug symbol was my own fault, when I forgot to plug the fuel pressure regulator valve connector back in after checking the solenoid continuity, resistance, and the presence of a voltage from the ECU. It only measures 4 ohms, I don't know yet if that is too low. It threw an open circuit fault when unplugged, so the ecu is monitoring the connection and the valve Pulse Modulated PCM voltage. Water ingress sounds plausible. The first turnover without start happened the morning after a 200km journey home in heavy rain. It started later that day, (Sunday), then let me down on Wednesday night. It started Thursday morning, then drove without issue for a week, during which I drove home in torrential rain. A few days later of perfect behaviour it just wouldn't start. Turns over, battery is new so it spins fast, but no start. Rail pressure stays low at 7900Hpa, though it rose to 10800 today when I tried it, still way below the 250000 required at idle. Tank low pressure pump is fine, I drained the tank with it as I though it ought have been dodgy fuel. I'll locate the ECU, pull it out and see if there's water about the connectors. One place too busy to take it on said it could be an injector seal, which can crack an injector and thus compromise the high pressure seal of the injector. I had a mild ticking/knocking sound on idle, which got quite loud if I floored it. There is also oily residue in the are of the bank one injectors. So many possible causes. This a short video of cranking. https://drive.google.com/file/d/15nhXSp52HFNzT3LDopFegVcYko6xbs3S/view?usp=drivesdk

@Bigdave1230,I'm trying to solve something similar. 3l V6 2015 quattro A6. I'm at cranking with no start. No faults showing on scans. Fuel rail pressure is way too low on cranking. The fault occurred slowly, car wouldn't start, then would an hour or day later. Sat down completely last week. When running it was perfect, but some starts had seriously rough idle, and swinging fuel rail pressure. I was tempted to take off the full pressure regulator on the drivers side. On my CRTE diesel there in only a pressure regulator on the front drivers side rail, a pressure sensor on the rear passenger side rail. The second pressureregulator is part of the high pressure pump, needs manifold and stuff off to access but as you say, it should default to limp mode. I only noticed the flashing glowplug light on the dash the other day. I presume you checked glowplugs, or maybe they don't power up if there is a fault elsewhere. Most places are aware of this rabbit hole of faults, and are reluctant to take on the car. Maybe I'll look for someone who can test the ECU.I'm not convinced its mechanical, as the car ran perfectly right up to stopping it (in the drive thankfully) before it refused outright since.