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Flashing glow plug light / No start


Bigdave1230
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Driving along with no problems then when I pulled up outside a friends house and dropped something off the glow plug light started flashing. Thought I’d best not turn the car off as it might not start so drive it the mile or so home and turned it off. Left it a min then restarted it with no problems, car ran fine with no warning lights or flashing glow plug light. Then next day jumped in the car and went to set off but the car cut out. Started straight back up and idled fine, rev’d no problem. Set off and after about 500 yards the car cut out again, started back up and after about 200 yards cut out again. Started back up and turned around to get back home and cut out again but then would start back up with a misfire and cut out after a few seconds. Couldn’t get the car home so rang a mate who turned up with a snap on code reader which showed injector circuit A & B malfunction as well as injector 2 malfunction and injector 4 electrical fault. Tried unplugging the injectors one by one to try and get the car to run if it was a faulty injector that was preventing the car from running but it would only run for a few seconds then cut out. Recovered the car back home but by this point the car wouldn’t start at all. After various checks the fuel pressure seemed low at the fuel rail ( weak and bubbly ) and the car not showing any codes due to it not starting so replaced the fuel regulator on the drivers side ( the car has 1 on each side but a faulty regulator on the passenger side will still let the car run all be it badly) still wouldn’t even attempt to start. The car would just turn over and over. Removed the injectors and set them for testing which showed various faulty. Replaced all 6 injectors with new but the car still wouldn’t attempt to start. Removed the ECU and sent away for testing with a description of the fault the car was doing. The ECU testing showed it to be faulty but beyond repair. Bought a used replacement with the same numbers on a through a friend of a friend cloned the ecu to match mine. Plugged back into the car and it fired straight up no problems with no codes stored or warning lights. After speaking with an auto electrician he believes that either a faulty injector spiked the ecu or an ecu fault killed the injectors. Found loads of posts on forums with cars with the same fault but no answer to what the problem was. Hope this helps if anybody has or gets similar.

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  • 2 years later...

@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. 

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HI Thomas, The common denominator between these two posts are the location of ECU . The previous post was probably due to water ingress. Because of the location of the A6 ECU , this also is susceptible to water ingress due to its location . 

Does the vehicle turn over ?  

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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

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Hi Thomas ,

1:You have checked the fuel pressure regulator EDU / ECM  ?  

2: ECU . I would refrain from taking readings from the ECU , so as not to cause damage. 

3:You have drained the fuel tank ? .. Did you prime the system from sender unit Low Pressure all the way to High Pressure Fuel Pump .

Did you replace fuel filter ?

Water ingress in ECU is internal and only visible once unit is opened PCB will have oxidisation . 

Do you have ODB reader fault codes ?

PS "  I would not take a reading from ECU using mustimeter as to limit damage to micro circuits"  

Jasonj 

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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.

 

Screenshot_20240212-040814_Drive.thumb.jpg.851b755101d635ccea83e293be7d459d.jpg

Here's the VAG 3l tdi clean diesel self study guide which might benefit members.

 

840193_3_0_TDI.pdf

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Hi Thomas, Notes 

1: Transmission fluid Drip Pan fitted .which is only visible using endoscope camera to access ,  that is where the dripping Transmission coolant drips into , so that's why its not on your driveway .

2: Transmission Coolant inlet valve . Seal can leak .

2a: system had been under pressure due to long drive. 

2b: background, vehicle was diagnosed with fault 2020 which was five years after manufacture , it is almost five years later .

3:Transmisssion OIL ATF is caustic 

4: Transmission would have been hot due to many gear changes from long drive Transmission  cooling system under pressure, (High Temperature )

5: Ambient outside Temperature starts to cool systems overnight . systems contract vacuum created wicking effect equalisation of pressure ( osmosis effect )

6: How to purge common rail .. Various methods . WARNING: This is very high Pressure and due to the fact you state that You Have not performed this task for a while,  I would be unable to advise due to the Danger Element , Risk Assessment Health and Safety .

7: FPRV valve . tap it on the sides just firmly with plastic tool . Do not use much force, only  gentle taps .

8: Battery :  Check health 

 

 

The fact There are no fault codes is strange 

 

 

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11 minutes ago, jasonj said:

Hi Thomas, 

Have you checked Cambelt Sensor ?Jasonj

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.

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Hi Thomas ,Re: Camshaft Position Sensor, Its just that this would be consistent with the symptoms you present . Because if oil were to compromise this sensor and so the signal sent would degrade . This in turn will cause the switching off of the fuel delivery and injectors . And as you mentioned this was an area of concern. And the fact you have an oscilloscope , this you could check Jasonj 

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Hi Thomas ,

1:  7900 hPa  hectopascals . is this the value relating to " Fuel high pressure, actual value " on your reader.?

2:  7900 hPa  hectopascals equates to 114.5798 psi,  pounds per square inch, is that correct ?

3  :What pressure should be in this systems,  High Pressure Rail System ?

4:  Fuel Pressure Release Valve, may be compromised. 

5: : OBD fault codes are there any ? Jasonj 

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1 hour ago, jasonj said:

Hi Thomas ,

1:  7900 hPa  hectopascals . is this the value relating to " Fuel high pressure, actual value " on your reader.?

2:  7900 hPa  hectopascals equates to 114.5798 psi,  pounds per square inch, is that correct ?

3  :What pressure should be in this systems,  High Pressure Rail System ?

4:  Fuel Pressure Release Valve, may be compromised. 

5: : OBD fault codes are there any ? Jasonj 

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.

Edited by Deezell
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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. 

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Hi Thomas, 

1: Crankshaft speed  0. 01 Is this right for turn over ? , I was under the impression it has to be 100 rpm  minimum 

2: Is this vehicle still turning over as normal operation but with no start ?

 

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On 2/14/2024 at 3:17 PM, jasonj said:

Hi Thomas, 

1: Crankshaft speed  0. 01 Is this right for turn over ? , I was under the impression it has to be 100 rpm  minimum 

2: Is this vehicle still turning over as normal operation but with no start ?

 

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.

Edited by Deezell
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Hi Thomas, 

1: Do you know what injectors are in this Vehicle  ie Bosch 

1a: The seal they are referring to is it : a :The Copper seal washer  b: The O ring   or The Injector casing   itself  or because it is not Torqued down ?

1b: The injector does contain  a  Solenoid at the Top with a Spring and Needle Spring and shim ( which is the part they change for calibration settings ) at the base of the Control Plunger 

The internal component's get Carbon build up and this can cause the needle to stick . 

Is the above relevant ?  Y/N

Because in 2015 this vehicle had a change to an uprated Injector

Do you have a part number ? 

OR is it this: Type,  BOSCH 0 986 435 360 Injector 

But you do not reference any Fault  Codes in relation to an injector fault 

High Pressure Fuel Pump  wait and see what happens ! 

Might just be, New Injector properly seated some  ceramic grease . Jasonj

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5 hours ago, jasonj said:

Hi Thomas, 

1: Do you know what injectors are in this Vehicle  ie Bosch 

1a: The seal they are referring to is it : a :The Copper seal washer  b: The O ring   or The Injector casing   itself  or because it is not Torqued down ?

1b: The injector does contain  a  Solenoid at the Top with a Spring and Needle Spring and shim ( which is the part they change for calibration settings ) at the base of the Control Plunger 

The internal component's get Carbon build up and this can cause the needle to stick . 

Is the above relevant ?  Y/N

Because in 2015 this vehicle had a change to an uprated Injector

Do you have a part number ? 

OR is it this: Type,  BOSCH 0 986 435 360 Injector 

But you do not reference any Fault  Codes in relation to an injector fault 

High Pressure Fuel Pump  wait and see what happens ! 

Might just be, New Injector properly seated some  ceramic grease . Jasonj

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).

Edited by Deezell
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Hi Thomas ,

Re ;  Your Quote  ( 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.)

1: ECU will be able to detect  Injector Faults . These typically being P10171 P0174 

2: ECU does store and retain Diagnostic Codes  Fault codes in its memory.  Hence the  expression" have you cleared the codes  ? "

3::ECU It also stores the Engine Maps. It uses tables to calculate., these are also retained in its memory . Along with Sensor Data .

4: From this Data the Dealer would have been able to call up this information as it works like a log which allows them to address any issues identified. 

13 hours ago, Deezell said:

the main dealers who sold me the car in 2018 noticed it on the first service

5: One of the visible signs of a leaking injector would be rev counter fluctuation when stationary with engine running  at Idle. ( rapid dancing up and down)

5a: ECU does know whats happening in each cylinder Jasonj 

https://www.ecutesting.com/categories/ecu-explained/

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