Help me understand fueling upgrades on my 2.7...

[01'C5 A6]

So my tuner is out of the country for another week..uuuugh!(hahaha)
C5 A6 2.7.. Jhm rs6 rs turbos\ 3"-2.5" stainless out the back\85mm m.a.f\630 cc ev14 injectors\ walbro 300 fuel pump.and stock 4 bar f.p.r
Now I originally had a Walbro 450 fuel pump In there and some knock off Chinese 630cc injectors but tracked two of them bad while getting remote flash.. Car ran great...gradually idled rougher and rougher until we stopped to get the miss going and dealt with (and also an oil leak quelled..)
I refused 2random replacements and bought Bosch's, they also have a multi hole plate instead of one giant hole...
In my late night frazzled state, read that I can have too much fuel pressure causing the injector to pressurize too much not letting them open properly and swapped out my 450 for a 300 walbro..
Car will start and die after maybe 2seconds...ideas??
Injectors say they're rated 3bar..I've read in a few threads where they're running 5 bar... Where the hell should I be?
How do I figure this out?
Any help is much appreciated... Been a spectator gathering knowledge here for quite a while and wouldn't trust info from any where but here!
Or a bently manual...but I think my answers aren't in there..

[chris86vw]

I refused 2random replacements and bought Bosch's, they also have a multi hole plate instead of one giant hole...

This is how they should be on a multi valve head. However if someone was tuning for improper spray pattern injectors before and they are changed to ones with a proper pattern they should be made aware of this change so they can adjust their strategy if necessary.

In my late night frazzled state, read that I can have too much fuel pressure causing the injector to pressurize too much not letting them open properly and swapped out my 450 for a 300 walbro..

while in theory too large of a fuel pump could result in too much pressure at the injectors this would really be the fault of other parts more so than the pump, like too small of a return line or faulty regulator. I believe the stock return line is fine for that pump. Basically the 450 is not going to over pressurize if all other parts are working. Voltage issues could in theory cause a pump to flow more, tied in with a restrictive return line could be an issue but you'd probably have other things you'd notice to go along with that.

Car will start and die after maybe 2seconds...ideas??

Was the pump your only change? if so then something like likely up with the install.

Injectors say they're rated 3bar..I've read in a few threads where they're running 5 bar... Where the hell should I be?

You should be where the tuner says you should be. Whether that is 3, 4, or 5 bar is up to them really unless you told them you are running a certain one and they tune for that.

Rated at 3bar means they flow the 630cc at 3 bar of pressure, they can run more (to a point) and less.. in theory but pattern would suffer and there is no point, just technically they can.

[01'C5 A6]

I swapped the Chinese single hole injectors out for the Bosch's with the multi-hole plate AND the fuel pump at the same time.
So I swapped the injectors first... Knock offs missing on 1&2 substantially. Put Bosch's in and run and dies...
Swapped pump thinking too much pressure. Same result..

[chris86vw]

I swapped the Chinese single hole injectors out for the Bosch's with the multi-hole plate AND the fuel pump at the same time.

Well then either something at the engine is unplugged/loose or it is the pump. Chance of it being an injector problem causing it to start and die after 2 seconds is slim.

Or its a lack of pressure having changed both, it may start and die a handful of times. IF you have tried say 10 times.. then I would rule out an issue related to depressurizing and look around.

[chris86vw]

So I swapped the injectors first... Knock offs missing on 1&2 substantially. Put Bosch's in and run and dies...
Swapped pump thinking too much pressure. Same result..

Ok edited your post while I Was replying.

If that is the case then likely not related to pump. Still likely not related to injectors but something is probably disconnected on the engine itself from doing the injectors. I'd pretend you are redoing them and check everything you touched.

[01'C5 A6]

Roger that... This where I'm at now!
Thanks for the reinforcement!!
I'll post what I find.

[Audibot]

Car will start and die after maybe 2seconds...ideas??

Just to be sure, the immobilizer didn't somehow get messed up with the tuning, did it?

[01'C5 A6]

Well, I in plugged maf. And it fired and rough idled!!
Dirrerent Maf. for 85mm housing req?

[jbain2]

Well, I in plugged maf. And it fired and rough idled!!
Dirrerent Maf. for 85mm housing req?

Use whatever MAF sensor your tune is designed for. I think most use the Hitachi but some are still using the Bosch. So it runs worse with the MAF plugged in?


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[julex]

Fueling is calculated from g/s of air flow (calculated by mapping of MAF voltage to air flow value) and injector flow rate (hardcoded in tune).

The g/s calculation assumes very specific MAF tube diameter.If you change the diameter - you change the reported g/s of air flow.

If you change MAF tube size or injector size (of FPR pressure) then you're pulling the carpet from under car computer's feet. The mixture will be off. If it is very minor, the ECU can compensate. But throw it off by more than 10%+ and you're in "no start" zone there.

[01'C5 A6]

Right on guys! The advice and direction, It's greatly appreciated!

[01'C5 A6]

So tuner has touched base with me but won't Log into my car... With the M.A.F sensor pluggednin it reacts like the immo. Is on, but it has been deleted.
If I unplug it she'll fire... ROUGH IDLE ALMOST diesel then something corrects and it idles nice and beautifully.. Any pressure to the throttle and back to dieseling... Plug MAF back in and dies...burns my eyes its so f'n rich!! Tuner says there is a major boost leak..
Now I've pressure tested and it leaks down... Over the course of 20seconds with the pcv off and plugged as well as the YPipe.. Super soapy water reveals nothing... I've ordered the silicone upgraded "spider hose" by JHM, just because they all need it.. But could this be the sole culprit behind the issues here?
I've cleared the codes but can't get it to run long enough (the dieseling noise scares the shit out of me) to get any lights or read anything with the vag com. ...

[01'C5 A6]

Swapped out to oem ecu..runs fine..super rich tho

[01'C5 A6]

Sooo. I yanked out the tuned ECM and put The stock OEM back in... Waaalaa! She runs and idles... Super rich and pretty doggy but she's alive!!
So I'm in Northern Colorado and looking for recommendations on a local tuner.. Thanks again for all the input!!

[m_haiser]

3zero3 motorsports

[chris86vw]

Now I've pressure tested and it leaks down... Over the course of 20seconds with the pcv off and plugged as well as the YPipe..

Not directly related to your problems, but yes of course a pressure test of this system leaks down.. it isn't sealed!

A pressure test only works if you keep applying constant pressure and search for leaks while it is under full pressure.


303 doesn't do any tuning like this to the best of my knowledge but they would be a good shop to run through the car to make sure there are no hardware issues before you throw money at a new tune.

I do know someone local (boulder.. may have moved to denver, not sure) who has done some PJ K04 and Tial cars, not sure if he has anything ready to go for a RS6 setup.

right now though you really need to get the car checked/sorted and confirm what you are using for fueling, maf size, sensor type, fuel pressure etc is what your current tuner wants you to be running before you think about going any further or spending money on a new tune.

Only have this guys personal number so don't want to give that out, if you PM me a phone number or email I can forward it to him. If 303 says they can tune this chances are it is via this guy anyway.

[01'C5 A6]

So, I finally got my tuner back into my ECU and turns out there was an error on his end saving the specs on the previous flash. He made some adjustments and its a smooth idle with lots more power! In a different rpm range tho... In the midst of getting used to it... 1st & 2nd collar locked me out of any more fun... Trans out now and waiting for my Jhm upgraded collars to show... Smh..lots of work on this beast...
Thanks for the heads up on 303 I've seen a little about them and will keep that in mind.