Q5 TDI 3.0 won't start

[Javier Neog]

Hi guys

I have a bad problem with my 2011 Q5 3.0 TDI with 26,000 miles. Everything works fine but engine won't start. As I turn ignition, the starter does its work but nothing happens.

I've looked through VCDS but there is absolutely no DTC error code. As battery ran out there appeared so many errors relating to Voltage appeared but I cleared them all.

Is there any common fault with these diesel engines? We do not know what to do.

- Fuel pump does work and rail have pressure.
- I can see combustion gases coming out from muffler and also from air intake.
- NO DTC error codes.

Any clue, guys?

Thank you in advance.

[Javier Neog]

Updates:


I've checked ECU and it seems fine. Pins still look as shiny copper and there is no signs of water. Below ECU there are some relays. None of them seem to be burned or damaged. I can read any values from ECU using VCDS, but cannot make some Output tests, such as Throttle valve control unit, that says: "this output is not supported by this module", or "refused by control module".


Tried again to turn on the engine with a new battery but still the same results. It does crank but doesn't turn on. What we found strange was the following:


- We could never read electric pulses in the injectors. Maybe we are reading them the wrong way? We tried using an LED indicator in the injector connector and no results.


- Gases were coming out from the intake manifold as if they were returning from the combustion chamber.


Hope this information sounds familiar to anyone here.


Have a nice day!

[M1tchy]

You haven't put petrol in instead of diesel have you?


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[Flash2]

Diesel injectors are normally tested using an oscilloscope and current clamp. Piezo type diesel injectors have a firing voltage of 100+ volts and the firing pulse can have a very short duration.

If one injector fails, the engine ECM shut's them all off. I'm pretty sure a trouble code would be logged though. You can disconnect the injectors one at a time and crank the engine. When the faulty injector is disconnected the engine will start but obviously there would be no combustion in the cylinder with the disconnected injector. So disconnect cyl1 injector, crank engine. If it doesn't start reconnect cyl1 and disconnect cyl2, crank engine and repeat for each cylinder.

Jim.

[Javier Neog]

M1tchy: there is no petrol in the system.

Flash2: Nice trick! I will try that this day. There is something strange though. I have no DTC errores. Yesterday I tried disconnecting an injector but still got NO error in the log. I think that is really strange because disconnecting anything should appear when I scan the ECU module. Am I wrong?

[Flash2]

Yes, I'm sure a disconnected injector would log a trouble code.
Is your VCDS communicating with the vehicle? Do you get plausible values in the engine measuring blocks and do they update when you crank (engine RPM & rail pressure)?
Another thing to think about too..the injectors wont fire at all if the correct fuel pressure isn't being built up in the fuel rail, so you want to check the rail pressure during crank.

[Javier Neog]

Thanks again Flash.

I will try all of your ideas. I can read ECU values using VCDS, but I am not sure where to find Rail Pressure in the blocks. Or do you mean measuring pressure using external tools such as manometer?

[Flash2]

No, check the rail pressure via the measuring blocks. The other way to do it is using a volt meter connected to the rail pressure sensor signal wire. You normally get 0.5V with just ignition on rising to about 1.3V during crank. Sometimes the diag tool looses communication with the ECU during crank due to the system voltage dropping so you can use the voltmeter test if that happens.

[Javier Neog]

Thank you Flash2.

I managed to read voltage directly from Rail pressure sensor. I could read initial value of around 0.5 Volt and increasing to around 1.1 or something like that while cranking. I read advanced meassuring blocks while cranking and these are some "interesting" values I could read.

While reading values I can see that the system (ECU) is actually sending signals to the injectors (loc. 051). Is this correct? Also I see that there is a pressure of 320,000 hPa. That is around 320 bar. Is this normal? Maybe I am reading values the wrong way.

http://www.vwaudiforum.co.uk/forum/attachment.php?attachmentid=26372&stc=1

We used diesel starter directly into the intake system so we could turn in the engine but still no luck. Instead we could still see exhaust gases returning into the intake system and also from this part of the engine.

http://www.vwaudiforum.co.uk/forum/attachment.php?attachmentid=26373&stc=1

I am really confused, and don't have a clue what to do.

Thank you very much for all of your help!

[Flash2]

Your fuel pressure readings are OK but exhaust gasses coming out the intake system doesn't sound good. Perhaps you have a blockage in the exhaust system. Clogged DPF perhaps?

[shabazmo]

Great post. I am not an expert but the crankshaft speed of 137/min seems very low. How was the car running before it did not start. Also if DPF problems then you would surely have a fault code. Basic checks would be to remove injectors and check compression. Then check fuel pressure, and then injection timing.Keep us informed of progress.

[Flash2]

Yeah, I did notice the low cranking RPM. And your right that a blocked DPF would normally log a code but he has been disconnecting injectors and sensors and it hasn't logged any codes...very strange.
But he is able to read the measured values so the scan tool is communicating with the ECM.

Exhaust gasses coming out the inlet makes me think there is a blockage in the exhaust. Probably not the DPF since I'm sure he would have mentioned that the light was on before the non start, but it could be a turbo fault or maybe even something as simple as the EGR valve being jammed wide open.

[Javier Neog]

Thanks everyone for helping me.

Here's the complete story. I bought the Q5 "as is" in an Auction. Seller told us that the Q5 was OK but it was under maintenance, so we bought it. When it arrived it came with NO injectors and NO high pressure pump. Before everything we checked the main fuel tank and there was only Diesel so I proceeded to buy the missing parts.

After assembling everything, it could not start. We didn't know what kind of problem it suffered before but we thought there was no petrol inside because only Diesel was coming from the tank. After many research I started calling everyone involved in the auction to find out what did happen in the past. The result: the Q5 was under maintenance because it was filled with petrol. I have find that out just TODAY and everything is much clear now.

Now that the Q5 is mine and the problem is also mine =( I must fix it. I just hope I haven't destroyed my new injectors and high pressure pump.

My new question is...

After changing High Pressure Pump, Inyectors, and cleaning everything that was affected, is there anything else we must do to the combustion chamber? Could it have damaged valves, pistons, anything?

[Javier Neog]

I am sorry about telling that Petrol wasn't the problem. I really didn't mean to lie to you all, it is just that I didn't know until now =(

[neilos100]

You haven't put petrol in instead of diesel have you?


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Someone knows his onions! :thumbup::thumbup::thumbup:

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[Flash2]

Ah, so there is a story behind it.

I don't know the engine that's in the Q5 but I've had a few VW diesel cars that have been filled with petrol and normally it's just a case of draining the petrol from the tank, clear out all the fuel lines and replace the filter. Fill it with diesel, bleed the system and the engine fires up, so I don't know why the HP pump & injectors would have been removed. Sounds a bit suspicious to me. If that was all that was wrong and someone started the job, why would they just abandon it with all the parts still removed.

Anyway, I hope you get to the bottom of the problem. Keep us posted on your progress.

Jim.

[Javier Neog]

I was told that the pump was destroyed from the inside because of petrol. Both pump and injectors were sent to the lab to be repaired meanwhile the Q5 was being sold. And then, a brave and wild buyer bought it. And yes, that is me! Now the problem is mine and have to solve it XD

I just bought a new fuel filter and ordered everything to be dissembled again so I can clean the entire system. I hope that my new pump and injectors weren't affected by any petrol remains. We didn't see any petrol though before assembly so I still have a little faith.

Any clue how to test injectors manually? I was told I must make a pressure test on them but I got no details on how to do it.

[Javier Neog]

Today's update:

Yesterday I bought my new fuel filter. Now I tried to empty the entire diesel tank so I connected the main diesel pump's output (the first one) to a hose and gave 12 volts. What was the result? Diesel is being pumped away but there's a lot of air coming out. I thought the tank was empty but the instruments board still says I have 1/4 the tank. Possible problems?

- Diesel level sensor inside the tank isn't working.
- Something is wrong before the pump. Bad connection maybe.

I will keep posting everything until I find the solution.

Here's the video:


http://www.abarrotesfaso.com/etc/IMG_3240.MOV

[shabazmo]

I am still on the low cranking speed of the engine. I know in some engines the diesel will not flow through the injectors if cranking speed is below 300rpm. Can you try and jump start the car, or is it an automatic.

[Javier Neog]

I am not sure about the cranking speed shown in the image. I did all by myself, pushing the break pedal, pushing the start engine button, lifting my laptop, pushing the print screen button in my laptop. Maybe I did the print screen in the wrong moment and I should try that again and post new values :)

Which values I should see at the crank speed?

I will continue tomorrow with this work. I think the next step is to find out why air is coming from the diesel tank pump. Sounds scary...

[Javier Neog]

UPDATE!

Hi guys. Sorry about delay answering my own post. We have fixed the problem finally! First I must say, that the only pieces I needed to buy after using petrol were the whole injector set and the high pressure pump. That's all.

So, what was the problem? There is a piece that holds down the injector. I don't know the name but please look at the picture one. We installed incorrectly (picture 2) so there was a leak in the combustion chamber through the injectors. When installing it correctly (picture 3), there was so much pressure and the engine turned on. I am so happy now. Don't worry about the rust in the pictures. That one wasn't installed in my Q5. Last photo are the people who helped me.

Thank you for all your help :)

Javier

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[shabazmo]

Well done. It just goes to show that basic diagnostics starting with compression, ignition and fuel is very relevant today but I am unsure how you would test for compression with the injectors in place. How did you get to establishing that there was leakage past the injectors.