RS5 Warm Start Issues

[croltean]

Not sure if anyone has had any similar issues with their 4.2 but I cannot figure this out.
The issue - the car has had intermittent start issues when it cranked after its been sitting for about 60-90 minutes. The car hard cranks and finally catches but stumbles and rough idles for a good 5-10 seconds and then smoothes out. I did receive sporadic multiple misfire codes.

My next step was to get the carbon cleaned - it was not bad at all for 65K miles, but had all ports cleaned put the car back together.

All worked great for a few weeks and the intermittent start issues started getting worse. Each warm crank started to take longer and longer again. (Cold starts were fine as the car started within 1-2 seconds)

I started doing some reading online and found about about fuel vapor locking due to faulty FPR/Fuel filter bleeding fuel pressure back into the tank. No codes at all in the system.

I went ahead and replaced the whole pump assembly including the filter and FPR. All went fine for about 2 weeks and yesterday the car started doing the same thing. Again no codes at all in the system.

Im at a loss now - I'm thinking it could be a leaking fuel injector / or maybe a injector seal leaking. Before I order and replace the injectors I wanted to see if anyone has had similar issues? Id hate to keep throwing parts at the car - but I cannot seem to get any fault codes out of it.

Ill try to post some videos in a little bit.

Any help or guidance would be appreciated

[JamesRS5]

I’m guessing you replaced the plugs?

[croltean]

I’m guessing you replaced the plugs?

Yes replaced the plugs and coil packs at 62k with this kit https://www.ecstuning.com/b-assemble...905115e~beukt/.

I did notice the stock plugs had 1 side electrode vs 3 side electrodes on the OEM plugs from ECS. I don't think that would cause any issues if anything provide better spark.

No misfires or ignition related codes in the system.

[superswiss]

Your symptoms are not exactly like mine, but similar. Get your high pressure fuel pumps checked. I've had misfire issues since around 35k miles that got progressively worse. Back when it started, Audi threw two cans of their fuel system cleaner in my tank and it went away for a while. Eventually I started to get warm start issues and check engines lights when driving the car hard at altitude with misfire codes being thrown. The engine turned over, but immediately died. After a few attempts I managed to get it running. It always happened when the warm car was parked for around 60-90 minutes like yours. There were no codes, other than occasional misfire codes, until one day it logged a fuel mixture too rich in bank 1 code. Took it in and dealer finally diagnosed the driver side HPFP malfunctioning and there was fuel in the oil. They replaced the pump, changed the oil, but a few days later I got some more misfires. I figured that the injectors might have gunked up from the bad starts, so I put a can of BG 44K in the tank, and since then all is good. Crossing fingers. I've had no cold or warm start misfires anymore. I suspect my HPFP had been on the fritz for a while, but just never bad enough to be easily diagnosed.

[croltean]

Your symptoms are not exactly like mine, but similar. Get your high pressure fuel pumps checked. I've had misfire issues since around 35k miles that got progressively worse. Back when it started, Audi threw two cans of their fuel system cleaner in my tank and it went away for a while. Eventually I started to get warm start issues and check engines lights when driving the car hard at altitude with misfire codes being thrown. The engine turned over, but immediately died. After a few attempts I managed to get it running. It always happened when the warm car was parked for around 60-90 minutes like yours. There were no codes, other than occasional misfire codes, until one day it logged a fuel mixture too rich in bank 1 code. Took it in and dealer finally diagnosed the driver side HPFP malfunctioning and there was fuel in the oil. They replaced the pump, changed the oil, but a few days later I got some more misfires. I figured that the injectors might have gunked up from the bad starts, so I put a can of BG 44K in the tank, and since then all is good. Crossing fingers. I've had no cold or warm start misfires anymore. I suspect my HPFP had been on the fritz for a while, but just never bad enough to be easily diagnosed.

I had the shop test the hpfp’s when they tested my in tank. All tested out to spec.. but what you said makes complete sense. A while ago car stalled out shortly after driving about a mile and came to a stop at a red light. I cranked it and it took a few turns until it fired up. I did log a lean fuel code on both banks. I thought it was due to the carbon build up. That issue has not resurfaced since the carbon cleaning. I will definitely look into the hpfps more.. I’d hate to get a cylinder washout due to fuel in the oil.

I appreciate the guidance !


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[Reggie]

I had the shop test the hpfp’s when they tested my in tank. All tested out to spec.. but what you said makes complete sense. A while ago car stalled out shortly after driving about a mile and came to a stop at a red light. I cranked it and it took a few turns until it fired up. I did log a lean fuel code on both banks. I thought it was due to the carbon build up. That issue has not resurfaced since the carbon cleaning. I will definitely look into the hpfps more.. I’d hate to get a cylinder washout due to fuel in the oil.

I appreciate the guidance !


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Have you tried a can of BG44K ?

[croltean]

Have you tried a can of BG44K ?

Not yet.. I’ve tried the vw fuel treatment / cleaner and the liquimolly cleaner


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[Ape Factory]

Man I swear I had a long reply, must have forgotten to hit the send button.

Going by your codes, I think James is right, it's the low pressure fuel pump assembly.

I can't see it being carbon buildup or just a bad injector causing fuel pressure issues. The low pressure feeds the high pressure pumps and there are two fuel pressure gauges on either fuel rail for the high pressure side. One would think they'd throw a code.

Worst case scenario, it's both the low pressure fuel system AND the #4 injector. Completely possible.

I would start with the low pressure fuel pump replacement and a can of techron fuel system cleaner. Far less expensive than BG44K and just as effective.
If that doesn't solve the fuel injector specific codes, you'll need to replace it. The RS5 injector is used in several VAG vehicles and it's not unheard of for them to go bad. Just does't happen often.

I heard there's a DIY video in this section for carbon cleaning which also has how to swap the injectors in and out. :)

The good news is if you're mechanically inclined, you can replace the injector yourself. If it's not a daily driver, all of the injectors could be sent out for cleaning/rebuilding and blueprinting, just to be sure. Otherwise you'd be replacing one injector with a new one and installing the "rebuild" kits on the rest which consist of a combustion chamber seal, o-ring and shim. More than possible to do in your garage.

If a shop's going to do the work, I'd have them carbon clean it while they have it apart. I'm sure it'll only add about $400 onto the cost since everything else that you'd normally do to replace the injectors has to be done to get to the intake ports and clean them. Another way to think of it, it'll cost you the price of one new injector over the price of a carbon cleaning.

[croltean]

Man I swear I had a long reply, must have forgotten to hit the send button.

Going by your codes, I think James is right, it's the low pressure fuel pump assembly.

I can't see it being carbon buildup or just a bad injector causing fuel pressure issues. The low pressure feeds the high pressure pumps and there are two fuel pressure gauges on either fuel rail for the high pressure side. One would think they'd throw a code.

Worst case scenario, it's both the low pressure fuel system AND the #4 injector. Completely possible.

I would start with the low pressure fuel pump replacement and a can of techron fuel system cleaner. Far less expensive than BG44K and just as effective.
If that doesn't solve the fuel injector specific codes, you'll need to replace it. The RS5 injector is used in several VAG vehicles and it's not unheard of for them to go bad. Just does't happen often.

I heard there's a DIY video in this section for carbon cleaning which also has how to swap the injectors in and out. :)

The good news is if you're mechanically inclined, you can replace the injector yourself. If it's not a daily driver, all of the injectors could be sent out for cleaning/rebuilding and blueprinting, just to be sure. Otherwise you'd be replacing one injector with a new one and installing the "rebuild" kits on the rest which consist of a combustion chamber seal, o-ring and shim. More than possible to do in your garage.

If a shop's going to do the work, I'd have them carbon clean it while they have it apart. I'm sure it'll only add about $400 onto the cost since everything else that you'd normally do to replace the injectors has to be done to get to the intake ports and clean them. Another way to think of it, it'll cost you the price of one new injector over the price of a carbon cleaning.

Hey Ape,

The first thing I did was the carbon cleaning - I did it as I had random misfire codes from time to time and also as preventative maintenance as I was over 60K. After the de-carb the car ran great for a couple weeks until I started getting warm start hard starts after sitting idle for 60-90min (car would turn over for 3-4 seconds and then stumble to a start). I then researched the issue and found other people dealing with the same issues. I ended up replacing the LPFP in tank fuel pump as well as the FPR and Fuel Filter as I was under the impression the car was getting vapor locked due to the fpr allowing fuel to return back into the tank. After I replaced the LPFP the warm starts got a bit better until the other day the car started doing the same thing.

Not sure what is next? Could it be a faulty fuel injector leaking while the car is sitting idle and flooding the cylinder causing the rough starts? I replaced all injector seals/gaskets when I did the carbon cleaning so it may be an injector going out - but no codes.

Could it be the HPFP going out?

I went ahead and ordered a can of BG - I will give that a shot before going any further. Weird thing is that there are no codes being thrown and I hate to just throw parts at the car.

Ive attached a video of the hard starts. If you listen closely there is a loud hum before I start the car and after it dies again. Not sure if this has anything to do with it.

[JamesRS5]

What sort of hum sound is it, electrical motor hum or leaking vacuum in a PRV diaphragm sound?

[croltean]

What sort of hum sound is it, electrical motor hum or leaking vacuum in a PRV diaphragm sound?

Sounds electrical to me


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[superswiss]

Hey Ape,

The first thing I did was the carbon cleaning - I did it as I had random misfire codes from time to time and also as preventative maintenance as I was over 60K. After the de-carb the car ran great for a couple weeks until I started getting warm start hard starts after sitting idle for 60-90min (car would turn over for 3-4 seconds and then stumble to a start). I then researched the issue and found other people dealing with the same issues. I ended up replacing the LPFP in tank fuel pump as well as the FPR and Fuel Filter as I was under the impression the car was getting vapor locked due to the fpr allowing fuel to return back into the tank. After I replaced the LPFP the warm starts got a bit better until the other day the car started doing the same thing.

Not sure what is next? Could it be a faulty fuel injector leaking while the car is sitting idle and flooding the cylinder causing the rough starts? I replaced all injector seals/gaskets when I did the carbon cleaning so it may be an injector going out - but no codes.

Could it be the HPFP going out?

I went ahead and ordered a can of BG - I will give that a shot before going any further. Weird thing is that there are no codes being thrown and I hate to just throw parts at the car.

Ive attached a video of the hard starts. If you listen closely there is a loud hum before I start the car and after it dies again. Not sure if this has anything to do with it.

That's one or both of your HPFPs, I'm 99% sure. Question is whether it's the left or the right one, or both. This is exactly what mine did. I forgot to mention earlier that my LPFP got replaced during warranty. It seems your car is following the footsteps of mine. Give it 25-50% and then start it, and once it kinda runs give it more or less throttle to keep it from dying until it stabilizes. That's how I got it to start in those situations. It was accompanied by a very strong exhaust smell. Check your oil, I'm guessing it will smell like fuel eventually.

[croltean]

That's one or both of your HPFPs, I'm 99% sure. Question is whether it's the left or the right one, or both. This is exactly what mine did. I forgot to mention earlier that my LPFP got replaced during warranty. It seems your car is following the footsteps of mine. Give it 25-50% and then start it, and once it kinda runs give it more or less throttle to keep it from dying until it stabilizes. That's how I got it to start in those situations. It was accompanied by a very strong exhaust smell. Check your oil, I'm guessing it will smell like fuel eventually.

I’ll see how she behaves after the BG treatment.. if nothing improves I’ll go ahead and order the hpfp’s.

I’m assuming you replaced the cam followers as well.. was there any wear on them?


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[superswiss]

I’ll see how she behaves after the BG treatment.. if nothing improves I’ll go ahead and order the hpfp’s.

I’m assuming you replaced the cam followers as well.. was there any wear on them?


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No, they only replaced the pump for bank 2. Tech notes say they found the spring and plunger for the pump to be faulty.

[Ape Factory]

That's one or both of your HPFPs, I'm 99% sure. Question is whether it's the left or the right one, or both. This is exactly what mine did. I forgot to mention earlier that my LPFP got replaced during warranty. It seems your car is following the footsteps of mine. Give it 25-50% and then start it, and once it kinda runs give it more or less throttle to keep it from dying until it stabilizes. That's how I got it to start in those situations. It was accompanied by a very strong exhaust smell. Check your oil, I'm guessing it will smell like fuel eventually.

No codes pointing to the HPFP? Obviously, hard starting can occur if there's not enough pressure regardless if it's the low or high pressure side. Those injectors are made to operate in a certain range and if the pressure is too low it either doesn't flow enough or the fuel isn't atomized appropriately making it harder to ignite. The HPFP's get HOT too...so if it's not under designed pressure, I could see fuel boiling.

[superswiss]

No codes pointing to the HPFP? Obviously, hard starting can occur if there's not enough pressure regardless if it's the low or high pressure side. Those injectors are made to operate in a certain range and if the pressure is too low it either doesn't flow enough or the fuel isn't atomized appropriately making it harder to ignite. The HPFP's get HOT too...so if it's not under designed pressure, I could see fuel boiling.

Nope, no codes pointing to the HPFP. In fact like OP, for the longest time there was no code, other than an occasional misfire on various cylinders. I even had the CEL come on, but it was always just a misfire code. Whenever it happened, I hooked up Carista just to get nothing more to narrow down the issue, until one day in a public parking garage it got so bad, that it took several attempts to get it started and then it logged a "fuel mixture too rich" code. I guess it finally got bad enough, that it would log a code and they were able to diagnose it. Using fuel system cleaners seemed to help for a bit, but eventually the problem came back. I think the bad starts ended up clogging the fuel injectors, which is why I think I was still having cold start misfires after the pump was replaced and it only completely cleared up after a can of BG 44K.

[Ape Factory]

Wow that's incredibly frustrating. You'd think, with all the sensors and the cross checking this car seems to do, it'd throw a code for a high pressure fuel issue.

So they were able to replace the plunger/spring in the pump or did they replace the whole unit? It's recommended the cam follower is changed if the whole pump is changed. I'm sure they wear and mate to one and other (pump and cam follower).

[superswiss]

Wow that's incredibly frustrating. You'd think, with all the sensors and the cross checking this car seems to do, it'd throw a code for a high pressure fuel issue.

So they were able to replace the plunger/spring in the pump or did they replace the whole unit? It's recommended the cam follower is changed if the whole pump is changed. I'm sure they wear and mate to one and other (pump and cam follower).

They replaced the whole unit. Maybe the cam follower is part of it. It's not showing up as a separate part. The part they replaced is 079-127-025.

[Ape Factory]

Yep, that's the latest part number (with an AL on the end, 079127025AL). The cam follower is 03H127307A for those DIY folks.


This pump is used on the following models...
Audi A8 4.2L V8 A/T Quattro Base Sedan 2011, 2012
Audi A8 4.2L V8 A/T Quattro L Sedan 2011, 2012
Audi A8 6.3L 12 cylinder A/T Quattro L W12 Sedan 2012, 2013, 2014
Audi RS5 4.2L V8 A/T Base Convertible 2013
Audi RS5 4.2L V8 A/T Base Coupe 2013, 2014

I believe APR makes an upgraded unit, it's $1200 and change for the rebuild of two pumps. Not sure how much more flow it's capable of and frankly, not even necessary at this stage. If you really search, I'm sure you could find the OEM pump for $400 each. JHM doesn't look like they make upgraded internals (yet!) and I can't find a rebuild kit for them anywhere and probably not feasible as I'd imagine the plunger/bore interface is pretty precise.

[croltean]

Yep, that's the latest part number (with an AL on the end, 079127025AL). The cam follower is 03H127307A for those DIY folks.


This pump is used on the following models...
Audi A8 4.2L V8 A/T Quattro Base Sedan2011, 2012
Audi A8 4.2L V8 A/T Quattro L Sedan2011, 2012
Audi A8 6.3L 12 cylinder A/T Quattro L W12 Sedan2012, 2013, 2014
Audi RS5 4.2L V8 A/T Base Convertible2013
Audi RS5 4.2L V8 A/T Base Coupe2013, 2014

I believe APR makes an upgraded unit, it's $1200 and change for the rebuild of two pumps. Not sure how much more flow it's capable of and frankly, not even necessary at this stage. If you really search, I'm sure you could find the OEM pump for $400 each. JHM doesn't look like they make upgraded internals (yet!) and I can't find a rebuild kit for them anywhere and probably not feasible as I'd imagine the plunger/bore interface is pretty precise.

I went ahead and ordered two new pumps (complete assemblies) and will swap them out this weekend. The issue presented itself yet again today.. long hard start and backfiring when I left the office. If the new hpfp’s do not fix the issue the only thing left would be the injectors. Hopefully I don’t have to go down that road- but we shall see. I appreciate you guys sharing your experiences and guidance.

As I said there are no codes so I’m kind of left in the dark on which direction to go.

I will update after the hpfp’s are swapped out.




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[croltean]

New hpfp’s arrived today and are installed. She started right up after the new pumps were primed. So far so good - it’s just a matter of time to test and see how things will behave.

I’ll have a few days to try it out before I go away for two weeks- so I will report back soon.




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[superswiss]

I'd recommend you run a can of BG 44K through with the new pumps.


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[croltean]

I'd recommend you run a can of BG 44K through with the new pumps.


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I put a can in this morning before filling up.. still have 3/4 tank - I believe that should be enough to clean out the system ?


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[superswiss]

I put a can in this morning before filling up.. still have 3/4 tank - I believe that should be enough to clean out the system ?


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Yeah, that should be fine.


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[BuyTheWarranty]

New hpfp’s arrived today and are installed. She started right up after the new pumps were primed. So far so good - it’s just a matter of time to test and see how things will behave.

I’ll have a few days to try it out before I go away for two weeks- so I will report back soon.




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Glad to see this resolved your issue! How long did the install take?

[croltean]

Glad to see this resolved your issue! How long did the install take?

Install was super easy.. the longest part of the install was to bleed the system of the fuel pressure. I put some rags under the fuel lines and loosened the fuel lines one pump at a time and let it do its thing. After than it was just a matter of removing the two bolts that hold the pumps in place. All in I think it was under 30 min for both pumps.

So far cold start this morning was great. Not a single misfire or hiccup.

Will continue to monitor it for the next few days.

Fingers crossed!



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[BuyTheWarranty]

Did you have to jack it up? What was your year and mileage? Maybe I missed that.

Perhaps it’s coincidence, but it seems the majority of RS5 issues on Audizine and A5OC are on the 2013 model, with the exception of Michaels? Maybe it’s just a mileage thing, as the RS5 seems quite reliable for the most part. Reason I’m asking is I’m out of warranty next month!

[croltean]

Did you have to jack it up? What was your year and mileage? Maybe I missed that.

Perhaps it’s coincidence, but it seems the majority of RS5 issues on Audizine and A5OC are on the 2013 model, with the exception of Michaels? Maybe it’s just a mileage thing, as the RS5 seems quite reliable for the most part. Reason I’m asking is I’m out of warranty next month!

I’m at 67k and it’s a 2014. I drive it pretty hard majority of the time and it’s been fairly reliable besides a couple things. In terms of the install I let it cool down for a few hours and went to work. No need to jack up the car - there’s plenty of room.
and do it before the intervals.

The only thing that failed on me was my t-stat at 48k and now hopefully the fueling issue is resolved.

Besides that I’m pretty ocd about maintenance. I’ve replaced the in tank fuel pump, did the carbon cleaning at 65k, replaced both of the pcv valves and full transmission service every 30k (gearbox and diffs), and replaced the accessory belt just in case. All these items were replaced as PM.

I felt the same when my warranty expired. But knock on wood she’s been solid. I’ve got a good Indy shop that tackles the stuff I don’t want to be bothered with.





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[croltean]

So a little update - about 250 miles since the hpfp swap and a full tank of gas. No more issues so far. Cold starts are solid and zero misfires. Warm starts and butter smooth as well.

Thanks to all that helped along the way! Hopefully this will help others with similar issues as we all creep up on mileage.




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[hahnmgh63]

FYI for those interested in doing the HPFP's, San Diego Audi has some of the best parts prices so it's where I do most of my business, the pumps (079127025AL) are $327.36, not cheap but a lot less than others. I didn't price the followers but I will probably do mine this summer (99k 2013 car). Also, when doing a powerful fuel detergent like the BG44 or the full strength Techron they do recommend and oil change after the tank of fuel as it washes a lot of carbon and gunk down into the oil system.

[ElliottRS5]

Hi, any more updates on the car I have the exact same issue so I am going to replace both HPFP. Just curious to see how yours is after some more mileage on it. Thanks

[croltean]

Hi, any more updates on the car I have the exact same issue so I am going to replace both HPFP. Just curious to see how yours is after some more mileage on it. Thanks

The warm start issue is gone after I replaced both of the hpfp’s. I’ve put roughly 4-5k miles since then. However, the lean codes and stalling issue still persists and still working on tracking down that issue.


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[ElliottRS5]

Any luck on the other issues ? I have still got this fault, car running rich on both banks, I thought it may have been the lambda sensors so went ahead and replaced those, as when driving the down shifts are very rough this is because the cars running rich. However I have noticed every time I put a petrol injector cleaner in the tank that fault seems to go away, why is this? The fault will then come back and I’ll keep having to use cleaners to stop the car from having warm start issues. All injectors have been out and cleaned when I did my carbon clean. Do you recommend I replace the HPFP? All tests I am doing on them are come back as fine. Also if they were faulty why is it when I put a cleaner through it’s solves my issues. Thanks

- - - Updated - - -

Any luck on the other issues ? I have still got this fault, car running rich on both banks, I thought it may have been the lambda sensors so went ahead and replaced those, as when driving the down shifts are very rough this is because the cars running rich. However I have noticed every time I put a petrol injector cleaner in the tank that fault seems to go away, why is this? The fault will then come back and I’ll keep having to use cleaners to stop the car from having warm start issues. All injectors have been out and cleaned when I did my carbon clean. Do you recommend I replace the HPFP? All tests I am doing on them are come back as fine. Also if they were faulty why is it when I put a cleaner through it’s solves my issues. Thanks

[croltean]

Are you getting any codes?


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[NoggieRS5]

I've got a different warm start issue... mine starts up and then you know how the revs go up and then right down? Mine stays at 1900rpm for a while (indefinitely) and suddenly goes back down. It doesn't sound normal and I have to lightly tap the throttle and the revs go down to idle. Stage 2 btw.

[SteveRS4]

I've got a different warm start issue... mine starts up and then you know how the revs go up and then right down? Mine stays at 1900rpm for a while (indefinitely) and suddenly goes back down. It doesn't sound normal and I have to lightly tap the throttle and the revs go down to idle. Stage 2 btw.

Mine is doing this I'm stage 2 as well ? Was told its the pump getting oil pressure up in the transmission ? It done this when i first flashed the ecu then it seemed to settle but its doing it again like yours ?

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[Woodepic]

I'm running into what sounds like a very similar issue on my 2013 RS5. This issue also sounds extremely similar to TSB 204672/4 for the 4.0T. I had that issue on my S7, and it sounds like I have the same issue on my RS5. If this ends up being the problem again, Audi really needs to learn to make reliable HPFPs lol.

I'll investigate and hopefully figure this out!