TDI Q5 wont start on warm engine

Hi guys

I am having a strange issue over here, but may be easy for any of you. I changed fuel injectors to my Audi Q5 3.0 TDI and high pressure pump. Everything seemed ok, but....

Cold engine:
I press start button, it cranks up for about 1 second and engine fires up. It always fires up on cold engine. I turn off engine and on again without problems.

After driving for some time until engine heats up, I turn it off. Then I press start button and engine wont start! It may start but sometimes I need to crank for about 30 seconds. It only happens when engine is warm. After I wait until engine cools down, it fires up with no problem.

I really have no clue and haven't found any answer over here. I thought I needed to drive constantly and problem would dissappear but it didn't.

** While driving, glow plugs start blinking for no reason.

I appreciate any help. Thank you very much!!

Javier

I know this is apples to oranges, but both fruit. I had a Yamaha outboard engine that exhibited the exact same problems as yours. Cold? Start immediately. Warm? Would crank and crank with no start. Would run fine for 30 mins no problems. Ended up needing a fuel pump replaced because of a design flaw that allowed to fuel pump to temporarily stop working once it became hot. Now I know this is likely not your case, but perhaps it is something to do with fuel.

The blinking glow plug light is trying to tell you something. Get the code read and let's work from there. You may need something more than just a generic code reader. VCDS or other dealer level scanner may be needed.

Hi guys. Thank you for your comments. I didn't receive any notification so couldn't read you asap. I did use VCDS to scan some values I think may be important, please take a look.

For what I know, TDI Q5 has 3 fuel pumps, one below rear seats, one in the mid-bottom near the fuel filter, and the last is the High Pressure Fuel Pump. Each one is really expensive, so I can't just buy new ones to test the problem

If there could be a way to test them individually?

These values were taken while cranking (warm engine), and no luck.

I am not sure, but I think value 181 means the actual fuel pressure. What do you think? 10,310 kPa is equal to 103 bar. Thank you very much!

If you are right about 181, then it seems that there is a problem there. We are all trying to learn about these engines so there isn't a hard he amount of hands on knowledge here, but if it were me I would pull the ful filter and check to be sure HPFP isn't making metal.

Check the fuel leakage from each injector, he may have "Excess Leak Back" via the returns.

We are about 60 days out for having a repair for these issues...

Mercedes Piezo injectors and the CBEA models for VW see this more often as they get in the 60-80K+ range...

The high Leak-Back exceeds the pumps output volume at cranking RPM's and fails to meet the minimum cranking pressure for starting. This commonly occurs when the engine is hot which is when the internals are expanded from heat and leakage rates are highest. The rail pressure simply does not pressurize to get enough pressure to start the motor.

If you can access the individual injector correction values, generally a deviation of less than 5.0 mm3 is preferred, more than that and you have a control or injector out of tolerance

After the repair they will be re-issued new injector control codes for each injector, coding will be required upon install.

Pete, do yo know if these can be checked the same way Duramax injectors are tested? They use graduated cylinders attached to each bleed-off port.

You can check them in a similar fashion, BUT keep in mind that there is always flow from the injector since there is a hydraulic control circuit used to fire the injector.

I would connect a collection container and run the motor for 30 seconds and compare actual leak back volumes. Its not exact but it will will clue you in on which injector(s) are causing the rail pressure loss.

Often the ECU injector control values "actual", indicate which one is most problematic in the set.

The combination of ECU data + Measured volume should key you in pretty closely.

Going back to the Duramax, there is a pressure relief valve on the end of one rail and it is prone to leakage. There is a hose that you can remove and with the engine running, there should be no leakage. One of ours was leaking a bit and would go into limp mode with a low fuel pressure code.

There appears to be a PWM controlled relief on the TDI engine, but I don't know if there would be leakage there at idle or not. Does the pump have enough control at idle to only feed as much as needed to the rail, or will it overfeed it requiring the relief to constantly be opening.

Would there be a spec for amount of leakage with a cold engine, or maybe it's just a seat of your pants measurement?

Hi!

I appreciate all of your comments. These days I've had no luck, but tested so many things. I won't turn on while it is hot and also there is so much white smoke coming out from the muffler (diesel smell).

Tests made:

1) Fuel pumps (before the filter) are doing good. I've tested them individually and they are pumping fuel in a good way.

2) Injectors were tested this way:
- Control codes were matched correctly.
- With the engine turned off, we have tested them for leakage by pumping air into the system and they met the minimum pressure standard (this method came from Elsawin).

3) Fuel pressure sensor was tested with volt-meter. It does give a 0.5 volt before cranking, then 0.6~0.7 while cranking, and finally 1.0 volt when engine is turned on. I am not sure about what does these value mean exactly but the way the signal (voltage) changes makes me feel it is doing good.

4) Leakage in the rail system was checked and we found nothing. Nor fuel leakage, nor bubbles, nor air.

Now 2 more test are to be made now.

1) Test the fuel pressure regulator in the rail system. This is the one attached to the end of the rail. There is a method I found at Elsawin, that consists of taking out the hose that comes from that valve in the rail system. That hose must not output any fuel in the first 10 seconds the engine is turned on. As far as I know there is no other method to test besides changing it Using VCDS i found a percentage (24.37%) and I don't know what that means in terms of functionality.

2) Test the fuel pressure valve. This valve is the one that comes from the injectors output, and seems like a little barrel, spin top like with 2 inputs and one output. I've found that my Q5 (2011) has a valve of a 2013 model, which is slightly different. Would this affect?

2011 - 059130218Q


2013 - 059130218AM


Thank you very much!

Javier

Drivbiwire said:

Check the fuel leakage from each injector, he may have "Excess Leak Back" via the returns.

We are about 60 days out for having a repair for these issues...

Mercedes Piezo injectors and the CBEA models for VW see this more often as they get in the 60-80K+ range...

The high Leak-Back exceeds the pumps output volume at cranking RPM's and fails to meet the minimum cranking pressure for starting. This commonly occurs when the engine is hot which is when the internals are expanded from heat and leakage rates are highest. The rail pressure simply does not pressurize to get enough pressure to start the motor.

If you can access the individual injector correction values, generally a deviation of less than 5.0 mm3 is preferred, more than that and you have a control or injector out of tolerance

After the repair they will be re-issued new injector control codes for each injector, coding will be required upon install.

Click to expand...

Hi guys.

One big question. What is the difference between the coolant temp. sensor & coolant temp. sensor at radiator outlet? They always have different values. For example:

CTS - 26 C
CTS-RO - 23 C

CTS - 62 C
CTS-RO - 22 C

Is this normal? Any clue?

OK I found the answer. Coolant temperature sensor warms up as engine warms up. CTS at radiator outlet is the temperature at the radiator output that is always colder. As radiator temp. rises until 90 C, then fans turn on.

Hi friends

I did all kind of tests to my TDI and finally I got (i think) good news.

As I told you before I found that I have a Fuel Pressure Maintenance valve of a 2013 Q5 instead of a 2011 model (pict below). I couldn't the proper instrument to measure pressure of the returning lines of the injectors (it must be 10 bars in the returning lines), so... I squeezed the line after the valve with a wrench, thus increasing the pressure (at least I think I did that).

The result? Engine turned on as soon as we squeezed the line. It was to good to be real so we removed the wrench and tried again. Result? Engine doesn't turn on. Again, using the wrench. Result? Engine turns on. I must say this ONLY happen when the engine is warm.

So the next move is to buy the proper maintenance valve and test my Q5.

Any comments will be gladly appreciated

Javier

My comment is good job on the back yard testing. Too often we get hung up thinking that electronic testing is the only way.

Hi friends!

I couldn't wait to share my progress with you all, even if it is not so good. I really enjoy learning about mechanics while I am just an Electronics Engineer. I am using ElsaWin to (at least) discard possible problems. It is awesome!

I did 2 tests today, one of them lead me to the possible fault in the engine.

1) Tested the pressure maintenance valve at the injector return pipes. That is, to place a manometer between injector return pipes and pressure maintenace valve. This valve is used to maintain around 10 bars at the injector's fuel return pipes. 10 bars is equal to 145 psi, and here is the result: almost 10 bars



This means that the tiny pressure maintenance valve is OK. So 2 more tests are left. Lets do another.

2) Test injectors. ElsaWin says I must measure fuels output at injector's return fuel pipes, that is, after the maintenance valve. Engine must turn on and stay at 600 rpm (idle) for 2 minutes and measure fuel return from injectors. It must be no more than 50 ml. Test results? 400ml. That is so much difference from teorical results and practical results.



This means (as I understand) that one injector is getting stuck, or at least, is having problems to stay open enough time. In few words? One or more injectors are bad. Next step is to test injectors one by one.

Does this behavior mean that injector is bad, or it needs cleaning?

Thank you for reading me!

Javier

Maybe I did not explain myself very well because of my poor english.
Fuel at high pressure enters injectors. Remaining fuel that is not injected into chamber is returned to fuel tank. All 6 injectors connect to a single point (pressure maintenance valve) in which pressure must be around 10 bars. This specification was succesful in my tests.
But... Total fuel returning from the 6 injectors must be 50ml or less running the engine at idle. I got 400 ml instead of 50 ml. I dont understand this behavior because i am not a diesel injector expert but the manual says one or more injectors are bad.
Does anybody know why an injector returns too much fuel instead of injecting into combustion chamber?
Thank you!!

you have a valve sticking open in the fuel system letting all the fuel to bypass the pressure needed for injection

Javier you are on the right track. Can you check return flow from one side of the compared to the other? If the flow is equal but still high, then all injectors are bad, but my guess is that this is unlikely since it seems to have happened suddenly. If one side if much higher than the other, that means you know which side has a bad injector. Now you need to do measure the get rn flow from each injector on that side.

Thank you wrenchman and whitedog for your comments.

wrenchman30:
Yes. Thinking on the whole system, if one injector's valve for returning fuel is stick open, then it is releasing pressure. My task for today is to find out which is the bad one.

whitedog:
Thanks for following my problem. Yes, I must find out which side and finally which injector is the faulty one. I cranked the engine (without turning on) and found out that one of the injectors is throwing too much fuel compared to others. I couldn't measure how much, but I can say the quantity was close to 1 ml per second, or less, but significantly more than others.

This is what worries me so much. Why did an injector broke up? Maybe it was already faulty, but, if it wasn't? I will bring another injector to test this situation, but before, maybe I am wrong, but should I test over-pressure in the system?

This is my big question: If my pressure regulator valve (at the end of the common rail) is clogged, causing overpressure, may this break one of the injectors? Pressure must be released somewhere, so it may damage something else? I did not open the common rail to clean the valve, but I think I must do this before something else gets damaged.

If I am wrong please let me know. The continous testing is risky, anything can get damaged so easy, lol.

Have a nice day!

Javier

It sounds like you have some injectors that are dribbling fuel and one injector that is squirting fuel. If so, then for whatever reason, I would say that is the bad injector. I understand you wanting to know why they fail and I don't have an answer for you. If it were my car, I would try to check the PRV and if I found nothing (or no way to check it) I would put an injector in and drive on.

Others likely have better advice.

Huge big update!

Fuel Injector change & Fuel Pressure Regulator Valve cleaning.

I changed one of the injectors that seemed to be bad. How do I know it was bad? Because it returned so many fuel while cranking. It took me like 3 hours to do the job.

I also removed the other 2 injectors from that side because the high pressure pipes (fuel input) were way too tight, I must say, impossible to remove. I needed to remove those pipes to remove the rail. Finally after removing all the necessary stuff I could take out the rail. Once outside I removed the pressure regulator valve and OH MY GOD it was full of miniature metal particles over there. I cleaned everything many times and used a magnet to remove any possible particle until I saw everything clean.

Assembly was easy and fun, really fun. Fuel system got purged (air inside) with VCDS. Cranked and turned on like a charm. It turned off automatically within some seconds and tried again and turned on. I left the engine turned on for 15 minutes until I got 50 C° and repeated off/on procedure. I couldn't believe it worked! I left the engine turned on for some more minutes and the problem disappeared entirely!

So, there were too faults over here.

1)
Problem: Injector malfunction.
Found by: measuring injector fuel output while cranking.
Solution: Injector replaced with another one.

2)
Problem: Dirty primary fuel rail & clogged Pressure Regulator Valve filter
Fuound by: 2Micron (from this forum) suggested me to do that.
Solution: Deep cleaning

Even the engine works well now, I still have 2 more problems to solve:
1) There is still a lot of white smoke coming from the muffler. Maybe I need to drive hours to purge everything in the engine exhaust? I don't know yet.

2)
Valve for Air Filter Bypass Flap (N275) open circuit. I do not know where it is but seems to be disconnected.

I hope this thread helps more people :9

Thanks to everyone!

Javier

Great job. Is there anyway to be sure that the metal in the valve came from the injector and not from the pump?

its from the pump failure and will be in the entire fuel system since it is behind the filter, if he doesn't get every piece of metal he will have future failures, with the engine fuel smoking at least one injector is trashed if not more

The metal in the valve came from another HPFP that got trashed because of petrol in the past. It was replaced with a new one, also 6 used injectors, new fuel filter, etc. Rails were not replaced, not the valve, that was my mistake. I checked the HPFP and it is OK, with no metal particles in its tiny filter.

I have been trying the engine and still works good.

So wrenchman, you say I still have trashed injectors? I have cleaned very well the passenger side rail but not the driver's side. That is because there is no hole to I can do the job. I will test injectors again tomorrow and see if they are faulty.

Thank you for your comments.