Intermittent hard or no start on 4.0T S6 S7 RS7- possibly solved

[Hofahome]

I wanted to create this thread to hopefully help others. I have been dealing with a very frustrating hard or no start issue, which only occurs after about 30 min to a few hours after driving the car. Never had issues with cold starts in am or right after starting the car up. Car drove great otherwise. Unfortunately no codes to help guide me and battery tested ok. All I could notice is that if the car was not turning over, I could push the throttle while it was cranking and the car would start up.

I'll save you the details about why other things like fuel pump did not make sense. I was going over the engine study guide and thankfully something stood out. The evap purge valve allows fuel vapors to be drawn into the intake and connects at the top of the charge cooler assembly. Unfortunately the evap (N80) valve would also hopefully throw a code if malfunctioning. However, there is a small one-way valve between the N80 valve and where the hose connects to the charge cooler assembly. It lies right under where the aluminum turbo intake pipes connect to the plastic intake assembly, or Roc Euro etc. if aftermarket. If this valve fails, then it allows fuel vapors to travel into the charge cooler. If the engine is off then enough time will pass so that fuel vapors collect in the charge cooler. When you go to start the car, the engine will draw in the fuel-rich air from the charge cooler and intake manifold, then will add of course more fuel via injectors, thus creating a rich AFR that will affect the ability of the car to start. It makes sense that the engine will start when pressing on/opening the throttle because it would allow fresh air in the intake, thus leaning the AFR back out. I hypothesize that when enough time passes (like overnight), the fuel vapors have enough time to dissipate outside of the intake tract and so there is no or minimal effect on the AFR of the intake air.

Of note, it might also cause the car to idle higher as well (due to rich condition in intake air), but I have not seen this in my car.

I decided to test my evap theory by unplugging the hose to the top of the charge cooler assembly after driving home today. An hour later I plugged the hose back in and started the car. It started right up. Well holy shit. Now, it does not prove that the valve is the cause of the issue, but at the very least the evap system is the culprit.

I then decided to look up the valve and unfortunately the valve does not have a VW part number on it and the evap schematics for the 4.0T (on places like audiusaparts) does not contain this info. Called up the local stealership and they were not helpful either. After literally an hour googling, I was able to find the part number. Here you go:

058905291B - This part can go fuck itself btw and audi needs to update their schematics. Sorry, I am just mad that I wasted so much time finding this thing.

Now, I have yet to change this valve out but should have it in later this week. If my issue returns, then I will probably look further into replacing the N80 valve too.

Hope this helps.

[aFOURstance]

Hope you guys find a solution

[pez81]

Man thank you so much. I need this it's driving me nuts. The S8 guys mentioned evap purge as well.

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[pez81]

That part number on ECS says does not fit our cars. You sure it's that one? Really appreciate you doing this mate I was ready to drive my car in to the sea for a Viking funeral

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[Hofahome]

That part number on ECS says does not fit our cars. You sure it's that one? Really appreciate you doing this mate I was ready to drive my car in to the sea for a Viking funeral

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The pic matches exactly the one on my car. Trust me, I am not going to put on a non-matching valve and risk fuel vapors building up.
I know how you feel about feeling like you wanna drive a car into a lake for a frustrating issue.
I’ll update when I get the valve in hand tomorrow. I paid for overnight shipping because it bothers me so much lol


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[pez81]

Thanks brother. I'll get one ordered and try it. Can't believe you solved an issue my shop or dealer couldn't

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[brian_216]

The evap issue happened on my wifes old a4 2.0t. After filling the tank it wouldnt start unless you gave it throttle. That is a good possibility in this case.

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[15 Phantom S6]

If that valve doesn't fix the issue, good chance the purge valve will. I've had a similar issue on a 2.0T and the purge valve fixed it right up.. When I fixed the issue, I replaced the evap canister and the check valve first, but it was only once I replaced the purge valve that the issue was fixed..

For my situation, it was apparently caused when filling up with fuel at the gas station. If you put any additional fuel into the tank after the auto shut off of the gas pump is activated (which I would do every fill up for the last 20+ years without issue on over 20 cars), additional fuel can get into the evap canister and some of the media (or whatever is in there) gets loose and travels downstream to clog up the purge valve..

[s4nicetry]

For my situation, it was apparently caused when filling up with fuel at the gas station. If you put any additional fuel into the tank after the auto shut off of the gas pump is activated (which I would do every fill up for the last 20+ years without issue on over 20 cars), additional fuel can get into the evap canister and some of the media (or whatever is in there) gets loose and travels downstream to clog up the purge valve..

Interesting, I should probably stop doing that then.

[MKEAudi]

I wanted to create this thread to hopefully help others. I have been dealing with a very frustrating hard or no start issue, which only occurs after about 30 min to a few hours after driving the car. Never had issues with cold starts in am or right after starting the car up. Car drove great otherwise. Unfortunately no codes to help guide me and battery tested ok. All I could notice is that if the car was not turning over, I could push the throttle while it was cranking and the car would start up.

I'll save you the details about why other things like fuel pump did not make sense. I was going over the engine study guide and thankfully something stood out. The evap purge valve allows fuel vapors to be drawn into the intake and connects at the top of the charge cooler assembly. Unfortunately the evap (N80) valve would also hopefully throw a code if malfunctioning. However, there is a small one-way valve between the N80 valve and where the hose connects to the charge cooler assembly. It lies right under where the aluminum turbo intake pipes connect to the plastic intake assembly, or Roc Euro etc. if aftermarket. If this valve fails, then it allows fuel vapors to travel into the charge cooler. If the engine is off then enough time will pass so that fuel vapors collect in the charge cooler. When you go to start the car, the engine will draw in the fuel-rich air from the charge cooler and intake manifold, then will add of course more fuel via injectors, thus creating a rich AFR that will affect the ability of the car to start. It makes sense that the engine will start when pressing on/opening the throttle because it would allow fresh air in the intake, thus leaning the AFR back out. I hypothesize that when enough time passes (like overnight), the fuel vapors have enough time to dissipate outside of the intake tract and so there is no or minimal effect on the AFR of the intake air.

Of note, it might also cause the car to idle higher as well (due to rich condition in intake air), but I have not seen this in my car.

I decided to test my evap theory by unplugging the hose to the top of the charge cooler assembly after driving home today. An hour later I plugged the hose back in and started the car. It started right up. Well holy shit. Now, it does not prove that the valve is the cause of the issue, but at the very least the evap system is the culprit.

I then decided to look up the valve and unfortunately the valve does not have a VW part number on it and the evap schematics for the 4.0T (on places like audiusaparts) does not contain this info. Called up the local stealership and they were not helpful either. After literally an hour googling, I was able to find the part number. Here you go:

058905291B - This part can go fuck itself btw and audi needs to update their schematics. Sorry, I am just mad that I wasted so much time finding this thing.

Now, I have yet to change this valve out but should have it in later this week. If my issue returns, then I will probably look further into replacing the N80 valve too.

Hope this helps.

Have you replaced it? Just bought an S6 for dirt cheap because it has this exact same issue.

[wwhan]

There is a TSB:

TSB 01 17 37 204672/4, October 4, 2017

01 engine sporadically difficult to start - 4.0tfsi

Update ECM software

[Hofahome]

Have you replaced it? Just bought an S6 for dirt cheap because it has this exact same issue.

Not yet. I was going to replace the evap purge valve too but have to order it.

Trying to look up the tsb now though. My question is if I can get the ECM updated while tuned? I have no OEM warranty so I could care less if the Audi gestapo gives me a TD1 designation.


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[OlyS6]

Not yet. I was going to replace the evap purge valve too but have to order it.

Trying to look up the tsb now though. My question is if I can get the ECM updated while tuned? I have no OEM warranty so I could care less if the Audi gestapo gives me a TD1 designation.


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You can, but then you'll need to find out if APR can then reprogram your ECU based on your latest revision of software. When software gets revised, some folks have to wait for APR to fix their tune to work with their new revision, in my limited understanding. Audi will rewrite your ECU, so you will certainly lose your ECU tune until your APR dealer can get it sorted.

[Hofahome]

Thanks Oly. Hopefully I wont need to do that.

To update this thread, I found out that Audi only sells the thing as an assembly, for $260. Wasteful and expensive if you ask me.

Part number is : 079133240BE (prior was AR)



I just ordered what appears to be the updated evap purge valve itself, which is like $30:

06H906517T

I bought some regular vacuum hose from local parts store and will use that in place of the hard plastic lines, unless I can remove the other ones without damaging them.

Btw, I am not a fan of where Audi put the evap purge valve. It sits right by the exhaust and under the wastegate actuator, plus both sides are shielded by metal. It’s just cooking in there.





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[pez81]

Thanks Oly. Hopefully I wont need to do that.

To update this thread, I found out that Audi only sells the thing as an assembly, for $260. Wasteful and expensive if you ask me.

Part number is : 079133240BE (prior was AR)



I just ordered what appears to be the updated evap purge valve itself, which is like $30:

06H906517T

I bought some regular vacuum hose from local parts store and will use that in place of the hard plastic lines, unless I can remove the other ones without damaging them.

Btw, I am not a fan of where Audi put the evap purge valve. It sits right by the exhaust and under the wastegate actuator, plus both sides are shielded by metal. It’s just cooking in there.





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Found it for £25 the complete kit

https://m.bestpartstore.co.uk/885488...alve-fuel-tank

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[Hofahome]

Found it for £25 the complete kit

https://m.bestpartstore.co.uk/885488...alve-fuel-tank

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Looks like that is not the same one


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[MKEAudi]

Thanks Oly. Hopefully I wont need to do that.

To update this thread, I found out that Audi only sells the thing as an assembly, for $260. Wasteful and expensive if you ask me.

Part number is : 079133240BE (prior was AR)



I just ordered what appears to be the updated evap purge valve itself, which is like $30:

06H906517T

I bought some regular vacuum hose from local parts store and will use that in place of the hard plastic lines, unless I can remove the other ones without damaging them.

Btw, I am not a fan of where Audi put the evap purge valve. It sits right by the exhaust and under the wastegate actuator, plus both sides are shielded by metal. It’s just cooking in there.





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Do you have pictures of where both valves are located? Will have both on Wednesday and want to get it done ASAP so I can drive the damn thing

[wwhan]

Do you have pictures of where both valves are located? Will have both on Wednesday and want to get it done ASAP so I can drive the damn thing

[Hofahome]

Here is one too. Not a great representation. The purge valve sits under #5 in the pic, which is at the back of the valve cover on the passenger side. You have to remove the metal shield and wastegate actuator (which is #5 in the pic) to access it. I think there are 6-7 total torx #30 bolts.




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[pez81]

Ah shame. Let me know how you get on if it fixes the problem I'll get one ordered. Hasn't done it recently but I haven't been overfilling with petrol. Wonder if that's one of the issues.

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[aFOURstance]

Curious also to see if this fixes the issue for you

[MKEAudi]

Doing this right now. Will post back with results when done

[MKEAudi]

Replaced both the non-return valve and the evap purge valve. No luck. The Audi dealer said it was the TSB for failing turbos that's causing the issue. Car goes in tomorrow for RS7 turbos and stage 3 tunes. Will update on if that solves the issue

[Hofahome]

Replaced both the non-return valve and the evap purge valve. No luck. The Audi dealer said it was the TSB for failing turbos that's causing the issue. Car goes in tomorrow for RS7 turbos and stage 3 tunes. Will update on if that solves the issue

Obviously we could have different issues, but I’m confused as to why my car would be running great otherwise in stg 3 form if the turbos were failing.


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[MKEAudi]

Obviously we could have different issues, but I’m confused as to why my car would be running great otherwise in stg 3 form if the turbos were failing.


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Car runs and drives perfect other than idle after it's been running more than a few minutes

[pez81]

Yeah I think he's having an entirely different issue to us.

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[aFOURstance]

Maybe check the turbo housings

[pez81]

I checked my turbos just for good measure and peace of mind, no shaft play, no scoring on the walls, no damage to the fins, and no oil in the housing, all signs that would indicate bad turbos are entirely non existent. However, hard start issue still persists.

Good to hear mate. I think if this evap valve doesn't fix it could be the fuel pumps. Does everyone with this issue have an aftermarket intake?

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[Hofahome]

So bad news and good news, kind of:

I installed the new evap valve and other valve. Car still has the hard start issue. Sorry I thought I was onto something.
I was sitting in the garage looking at vag com values. My long term fuel trims are like -4% and -5%, nothing crazy but pointing to fact that my car is "wanting" to run rich, and of course the ECU adapts.

Interestingly, it looks like our ECU keeps low fuel pressure up after turning the car off for like 10min (I'm only guessing and was not timing it). After that you can see the low pressure drop pretty quickly. When I press the start button again, the low pressure raises to near spec very fast.

The biggest thing I noticed is that the high pressure actual readings stayed very high. IN FACT, the high pressure and rail pressure readings were about 3 times as high as specified, which is a major clue. I was looking at the high pressure and rail pressure values to see if I saw a drop, which would point to a leaking injector if true. However, the pressure raised a little over time, probably due to the heat of the motor after being turned off.

When I went to start the car (total sitting time of probably 20min), it did its typical thing. Almost like it wants to start right away but stalls. I saw the high pressure go down about half of what it was. Tried again and same thing happened. The high press at that point was near spec. I waited a min for some of the fuel in the cyl now to dissipate. Started the car at that point without issue.

So basically the fuel pressure on the high side is WAY too high and staying that way. Finding the reason for this will likely provide the answer to our problem.

[pez81]

So bad news and good news, kind of:

I installed the new evap valve and other valve. Car still has the hard start issue. Sorry I thought I was onto something.
I was sitting in the garage looking at vag com values. My long term fuel trims are like -4% and -5%, nothing crazy but pointing to fact that my car is "wanting" to run rich, and of course the ECU adapts.

Interestingly, it looks like our ECU keeps low fuel pressure up after turning the car off for like 10min (I'm only guessing and was not timing it). After that you can see the low pressure drop pretty quickly. When I press the start button again, the low pressure raises to near spec very fast.

The biggest thing I noticed is that the high pressure actual readings stayed very high. IN FACT, the high pressure and rail pressure readings were about 3 times as high as specified, which is a major clue. I was looking at the high pressure and rail pressure values to see if I saw a drop, which would point to a leaking injector if true. However, the pressure raised a little over time, probably due to the heat of the motor after being turned off.

When I went to start the car (total sitting time of probably 20min), it did its typical thing. Almost like it wants to start right away but stalls. I saw the high pressure go down about half of what it was. Tried again and same thing happened. The high press at that point was near spec. I waited a min for some of the fuel in the cyl now to dissipate. Started the car at that point without issue.

So basically the fuel pressure on the high side is WAY too high and staying that way. Finding the reason for this will likely provide the answer to our problem.

Well done and thank you mate. Do you think it's related to atmospheric pressure or temps? I notice it more when there's a change from warm to cold or cold to warm out. Also if there is an ECU update for this as someone mentioned then maybe it is just ECU related. Thank you for trying the part and letting us know. Mine did it twice today and the last time there was over 2 hours in start ups. That's the longest I've had it before. You give it a little throttle and she bursts in to life.
I have used boostane in the past and actually it started after I did that. Not saying it's related but just trying to look at every possible reason. I don't think it's the turbos I had mine checked when the downpipes went in. If it's not the evap then could it be injectors, hpfp, fuel pump in the tank or ECU?

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[pez81]

Maybe we should share all mods, fuel used, model year etc?

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[pez81]

Don't know if you've seen this before but might be useful

https://www.audiworld.com/forums/a8-...oblem-2915178/

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[Hofahome]

Shit. Mine seemed to come up after using boostane as well. I have run a bottle of BK44 fuel cleaner through it recently but obviously not helpful.
Going to keep reading, but I think the fuel metering valve on the HPFP is malfunctioning.

[pez81]

Shit. Mine seemed to come up after using boostane as well. I have run a bottle of BK44 fuel cleaner through it recently but obviously not helpful.
Going to keep reading, but I think the fuel metering valve on the HPFP is malfunctioning.

Could it be boostane just rotted something? I remember I bought a bottle used it then within a week or two the issue I think first occured. I'm pretty sure of it. Maybe the methanol content was too much for the fuel lines? But why does it only happen after a short cool down, that doesn't make sense? It was before I went stage 2 as well so I don't think it's that. So if we rule out turbos for now as you've got new turbos and mine were checked what does that leave?

Hpfp
ECU
Fuel lines
What else?

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[pez81]

Another user wrote this.

One more check idea you can also do as a DIY, and unrelated to fuel pump idea. You say car stalls if you run it, then park for an hour or two outdoors, then restart. So, if you can replicate that, before the restart, try opening gas cap and see if system is pressurized (likely). Let off pressure. Now try to start. See if any different result. If so, maybe something in the fuel vapor recovery system. Not a common Audi issue, but just going by some of the symptoms you describe--that is parking outside, which I'm guessing means sun/hot this time of year, which could be loading up vapor recovery system.

*Reply




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[pez81]

Hoff have you seen p3u solved his start up issues?

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[MKEAudi]

Seems like several people have gotten the issue sorted out by replacing the HPFPs. If new turbos don't do the trick for me I think that will be next on the list to replace.

[aFOURstance]

Seems like several people have gotten the issue sorted out by replacing the HPFPs. If new turbos don't do the trick for me I think that will be next on the list to replace.

SRM makes a fueling upgrade kit

[pez81]

I read trying the gas cap before you restart just to purge the fumes. I'm going to try it. Strangely car hasn't done it today. But it's quite cold 8 degrees at the moment. Always seems better when it's below 10-12 degrees.

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[Hofahome]

I have some days off next week. Going to log between that time but will probably take my car in. I have aftermarket warranty so hopefully the high pressure pumps are covered. I’ll probably have them pull the fuel rails too and check/clean them.

Btw, it might be worth replacing the low pressure sensor, which is actually on the driver side hpfp. If this is underreporting, then the high flow metering valves in both pumps are going to let more fuel through than should be.


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