Weird hot starts

[Milen02]

Hey everyone,
for the past few weeks my car has been acting weird on engine starts when the car has been driven and is turned on again. About 1 in 5 times the engine turns and then stops doing as in the video, yesterday after doing that thing and on the second start it turned for a good 2-3 seconds and then started. Not sure if it is important but worth mentioning I changed the 110aH OEM battery with a new 110aH Varta a few weeks ago, I think I had this problem with the old battery too. Audi A6 2012 034Motorsport stage 2+. If any of you have any ideas what could be causing this I would be very thankful.

youtube.com/shorts/XSkgAnkACY0 (sorry for the radio it turned on by itself).

[Milen02]

Did auto VCDS scan and there are no faults.. so far I worked out it only happens when car is hot and has been left for some minutes to an hour, if I stop it and start instantly there are no problems. The problem occurred pretty much every start now and when it starts the car shakes a bad. Pretty much lost now after seeing no faults..

[f4m0u5]

im guesing a leaking fuel injector.

run the car till warm, then shut off the engine. plugin vcds and look at fuel rail pressure.

wait 5 minutes and check were the pressure is at. it should rise up to like 120 bar.

[Milen02]

I just did the test and when the car was on the pressure was about 37 bar after engine off and waiting 5 minutes it went up to 70 bar and kept going up slowly, injectors shouldn’t be the problem

[MattyMarkey]

Fairly certain these are symptoms of a failing HPFP (hard starts when warm). Do you smell fuel under the oil cap?

Check out this TSB and perform the low pressure test (indicating failing HPFP); you performed the high pressure test (indicating leaking injector): https://static.nhtsa.gov/odi/tsbs/2018/MC-10133288-9999.pdf

"Also, observe the pressure build-up of the low fuel pressure after switching off the engine. In the first five
minutes the low pressure must rise above 6 bar and the pressure must be held for another 10 minutes. If
the low fuel pressure was built up correctly but drops by more than 1.5 bar in the first 15 minutes, it can be
assumed that at least one of the high-pressure fuel pumps is leaking. In this case, replace both high pressure fuel pumps and change the engine oil."

[Alabama]

Fairly certain these are symptoms of a failing HPFP (hard starts when warm). Do you smell fuel under the oil cap?

Idle curiosity. The TSB mentions the following: "The evaporation process of fuel in the engine oil starts at about 122°F engine oil temperature." Might this be why the engine oil temperature gauge starts registering at 140? When the oil temp starts displaying, the driver is informed that the evaporation process has started, and I'm not a member of the group described as "an extreme short distance operation profile of the customer."

[Milen02]

I plugged the vcds and mine doesn’t have the low pressure. I only have Fuel pressure IDE00589 and Actual fuel rail pressure ENG101818

[Milen02]

Adding pics with available values

ibb.co/vc7wSQ6
ibb.co/4SLMP6H

[MattyMarkey]

Adding pics with available values

ibb.co/vc7wSQ6
ibb.co/4SLMP6H

Can’t see pics. Does your oil cap smell like fuel? Indication of leaking HPFP


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[Milen02]

The cap did smell like fuel, ended up changing the HPFP and the oil. Today it didn’t start again..

[MattyMarkey]

The cap did smell like fuel, ended up changing the HPFP and the oil. Today it didn’t start again..

Oofta... Changed one or both HPFP?

[Milen02]

I dropped it off to a mechanic in my town and he said it’s most likely the HPFP and changed it.. does the car have two pumps lol?

[MattyMarkey]

I dropped it off to a mechanic in my town and he said it’s most likely the HPFP and changed it.. does the car have two pumps lol?

It sure does haha. One on each side, front of the engine. Cannot miss them. Just might want to confirm with your mechanic...

Take a look at this post, has quite a few good pictures and diagrams: https://www.audizine.com/forum/showthread.php/887221-SRM-Install-Guides

[f4m0u5]

I dropped it off to a mechanic in my town and he said it’s most likely the HPFP and changed it.. does the car have two pumps lol?

one pump for the 3.0t two for the 4 0t

[f4m0u5]

I just did the test and when the car was on the pressure was about 37 bar after engine off and waiting 5 minutes it went up to 70 bar and kept going up slowly, injectors shouldn’t be the problem

re try the test i put above if you already tried replacing hpfp. make sure engine hot. get the high presure fuel pressure at engine off. and at 5 minutes. and at this point i would just keep watching it evry few minutes to see how high it gets. and then maybe even how long it holds the max lressure you get or if it peaks then starts falling off.

[Milen02]

I replaced the HPFP indeed, redid the test and it went as follow:
Turned engine off when hot.
After 5 minutes : 64 bar
After 10 minutes : 82 bar
After 15 minutes : 91 bar
After 22 minutes : 97 bar
After 31 minutes : 92 bar
After 33 minutes : 90 bar
After 35 minutes : 87 bar
After 37 minutes : 85 bar

[Milen02]

wait 5 minutes and check were the pressure is at. it should rise up to like 120 bar.

For me it didn’t go over 100 at any point.

[f4m0u5]

For me it didn’t go over 100 at any point.

accordong to audi it only needs to see 80 bar after 10 mins.

but my car is at 45bar when i shut engine off and rises to 122bar within 5 mins and after 15 mins it was at 143 holding steady( may have already been there since 10 mins)

i just started the for 5 minutes and then shut it down and checked.

https://i.imgur.com/ZltyakO.jpg

[Milen02]

Dropped the car off to my mechanic to check the injectors.. update soon

[Milen02]

Result was 6 leaky injectors, after inspecting them bosch said it's most likely due to the 034 tune, personally I think their time just came since the car has about 135k miles.

[MattyMarkey]

Result was 6 leaky injectors, after inspecting them bosch said it's most likely due to the 034 tune, personally I think their time just came since the car has about 135k miles.

Oof. That’s rough. Kudos to F4m0u5 for getting that one, even though not ideal.

Injectors don’t fail often in these platforms, even at higher mileage, so I can see some merit to the tune; at least exacerbating the issue


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[AudiInMyA7]

one pump for the 3.0t two for the 4 0t

Dont forget the lpfp in the tank


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