Audi A3 2.0TFSI (BWA) Intermittent starting issue

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Sharkie1976

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Hi all.

I have been having this issue for some time now and would really love to get to the bottom of it.
Car: Audi A3 2.0TFSI (57)
Engine: BWA.

The problem is that every morning (mainly cold at the moment, but also when outside temperatures are nice), the car fails to catch on cranking.
After the first start of the day it is normally fine afterwards, but does sometimes do this later in the day or when I leave work it does it too.
Once started it runs absolutely fine.

When I turn the car over it turns well, so seems like starter is fine.
Battery is new within the last 3 months.
The revs raise to about 450 rpm and then drop quite low to 250rpm, but then raise again and it fires up.
Some days it's worse than others.
On rare occassions it needs a second crank.

I have recently changed the following items:
New plugs.
New coil packs.
New Air filter.
Oil & Filter Service.
New fuel filter.
New Coolant Temperature Sensor.
New Cam follower.
New battery.
Also, checked the Air Temperature Sensor with an Ohm meter and it seems that the readigns are fine when heated and when put in the freezer to cool to a low temperature.

I do have a genuine VCDS cable and it gives me no errors on auto scan.
All temperature sensors give a true reading when checked.
Fuel pressures seem good, but I'm not 100% sure on that. Would the car even start if the fuel pump relay was intermittent.?
I have carried out basic settings on Thottle Body, Intake manifold flaps and fuel pump.
I'm now totally stumped.

Can anyone suggest any ideas, or anyone experienced a similar problem.

Any advice would be greatly appreciated.
Thanks,
Rob.
 
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Uwe

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I understand not wanting to re-post an Auto-Scan of your car in every new thread you start, but it would help if you'd include a link to a post where there's already a scan from your car, like this. ;)

-Uwe-
 
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Sharkie1976

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You absolutely right Uwe, sorry keep forgetting that.!
Thanks for doing the link on my behalf.!
Appreciate it.!
 
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Dana

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FSI engines are usually extremely good (borderline annoying) about telling you when a low fuel pressure problem exists ... but can you confirm/hear the electric in-tank pump running when you first open the driver's door?

If not I wonder if the driver's door latch micro switch is faulty and not sending the comfort signal to wake the ECM.

If so, make sure it doesn't sound sick. Another thing you may want to do if this is time based, as opposed to temp specific, would be check the live initial starting and residual fuel pressure with an actual gauge. If you try to use VCDS MVBs and this is a fuel problem simply turning the key on to communicate may prime it and fix the issue.
 
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Sharkie1976

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Hey Dana.
Firstly I'd like to say thanks for replying to my post, greatly appreciated.
You made some valid points there.! Since owning the car for a year now, I have NEVER heard the fuel pump priming when opening the drivers door. I'm going to have a look at the workshop repair manual to check the wiring diagrams to see if it shows me any wires or switches that should be making comms with the low pressure pump. I believe it is under the rear seats but have not had a look yet. It's currently raining here in the uk (nothing unusual). Is there a way of testing the door switch, I know it activates the interior lights ok and the door open picture illuminates in the dash display. Would that be the same switch that possibly activates the LP fuel pump.? Or could there be another switch.?
As for the VCDS I totally agree that having to have the ignition on to get connected will not help me to see pressures within the lines when it's been sitting overnight. Unfortunately I don't have a pressure tester at present, but may be able to get hold of one if absolutely neccessary.
I'll check out the wiring diagrams (which could proves tough, for me anyway, lol).
If anyone ekse can confirm that there should indeed be an audiable sound from the LP fuel pump, I would be very grateful.
Thanks again Dana, I'll hopefully be back with some info over the weekend.
Rob.
 
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Sharkie1976

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Ok, I had a look through the wiring diagrams and couldn't managed to find any switch related to a door switch. I am rubbish at wiring diagrams.!! It did show switches, but doesn't show where they are located within the car. I've managed too find the fuse (No 27) on the drivers side removable panel and fuel pump relay. Will look at the fuse tomorrow.
I also removed the rear seat and under it is the LP fuel pump. Opened drivers door, no sound from it, turned ignition on, no sound from it. I'll have another listen tomorrow and see if I can hear it prime in the morning.
The only reason I can think of, is that it only activates when ignition is turned to start the engine, but can't seem to find out any info if that is the case.
Also took a look at the drivers door, and there is no switch (like a button that pushes in or out) that is activated by opening the door.
Hope somebody with the same car can shed some light on this.
Thanks!
 
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Dana

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Hi Rob,

The Comfort Bus (combo of the 42: Door Elect. Driver controller, Driver's door latch switch and 46-Central Conv. module) should send that door open/wake the fuel pump signal. The switch on these vehicles isn't a spring loaded button like the good old days, the newer cars (roughly Mk4/1999 on the VW side) have a micro switch inside the door latch itself. The switch is normally called F220 in the wiring diagrams (if you need or want to locate it).

I would check that at some point in the #42 controller, MVB 005.2 which is labeled; Contact Switch (F2),Driver Door,Range: Door Open/Door Closed

If the readings work every time you open and close the door and the dome lights turn on/off under normal circumstances, I would not suspect the door latch is at fault.
 
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Sharkie1976

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Hey Dana.
Thanks very much for the additional information. I did read through the workshop manual and is says that the LP fuel pump does prime when the drivers door is opened.
It says that the motor is very, very quiet and lasts for only 2 seconds. Well, I'm not that fast, so first thing in the morning I got my wife to open the door after I removed the rear seat and held a screwdriver to my ear to amplify the sound, and it does indeed make a audiable sound. So I guess that rules out the LP fuel pump.
So fuel supply to the engine seems to be fine. I will look at the VCDS #42 controller when I next attach it, just incase it's intermittent (you never know).
Other than that, I'm trying to think of where to go next.
Any pointers would be appreciated by anyone.
All the best,
Rob.
 
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Jack@European_Parts

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Hello Robert........

Well I bet you are losing a terminal 15........ either function of relay, or during the cold start with an ignition switch which is fubar in crank position, and no terminal 15 feed during the terminal 50 commencing. ( most likely )

Be sure to observe J271 ecu supply relay during condition for 15 and terminal 30 via J317 and BUS support in engine bay supply via J757.

Double your pleasure .........Do not omit the onboard control supply relays for terminal 30 or terminal 15 or........X J59
( known as supply relay 2 for both onboard supply 0x09 ) so dumb...... but hell lets complicate it further.

A faulty ground during crank load to a cold engine......... can cause condition you aforementioned.
 
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Sharkie1976

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Hey Jack.
Very kind of you to chip in with some good information. Hopefully you're onto something here mate.!

TBH electric circuits and wiring are something I'm not too familiar with (sorry). Can you help me out with what I need to do, and where these items are and how to check them.
I understand if you don't want to commit too much time for someone like me, but I'm hoping that you enjoy resolving these kind of problems for your little reference book for future use ;O)
I understand that Terminal 15 is to do with the ignition switch (I think), and Terminal 30 is more to do with the battery side of things? Terminal 50 to do with Starter motor solenoid.?
Is the J271 relay under the drivers side footwell panel, and the J317/J757 relays in the fuse box alongside the battery under the hood.? and are these what I ultimately need to check.?
Are there also fuses associated with these relays that would be worth checking first.?
Also, would the car still start if any of the above were faulty (or can they gradually wear out and essentially die.?)
Many thanks for your time, I hope you can be of further assistance.
All the best,
Rob.
 
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Sharkie1976

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Hey again.
I'm going to look at the current flow diagrams on the workshop manual tonight.
I think Terminal 15 is Relay R1 under the bonnet. If I recall I did ask on another forum last year (but didn't get a response) as to what this relay is, as it was getting rather hot to touch.
Hopefully this ties in with what you have described Jack. Should this relay be getting quite hot, or does this show that it could potantially be faulty/intermittent.?
Thanks,
Rob.
 
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Jack@European_Parts

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I would be happy to help.......

Please get and RTFB the repair manual.
Read how to read WD or see this link Jef made.

http://forums.ross-tech.com/showthr...d-wiring-diagrams&highlight=read+wire+diagram

This is a nice link Uwe left the other day.

http://en.wikipedia.org/wiki/DIN_72552


Terminal 15 is B+ switched voltage..........whether via switch such as ignition switch or switched relay!

Keep in mind that there are multiple Terminal 15 and 30 relays not just one leg current track anymore.
ECU supply relays and FP or load reduction relays........... may in fact be switched after a controller is powered up, with a preliminary input or virtual terminal such as a wake via the Gateway 0x19 or 0x09 BCM.

Keep in mind ground is what is switched which why I say check them!

Beware:

The term ASSHOLE ground is very important to understand and test proper.
This is where you have a ground with a meter or test light through a device, however an incomplete ground........
I call it this because you will always feel like an asshole after you find it and thought you tested it correctly......... when you didn't.

In addition to things such as voltage drop.......... during crank under load, and loss of needed current to operate a controller to cold start.

I often install voltage stabilizers with capacitance in my race cars on specific tracks to maintain a clean current for such clarity.

It is also why the OEM has moved to duel isolated BDM battery managers for such common conditions during the load of cranking.
 
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Sharkie1976

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Hey Jack.
Thanks again for your reply and suggestions. It does sound very complicated, but I'm going to have a good read of the links you kindly directed me too.
Once I have a better understanding, and can follow the diagrams from the manual I'm hoping it will help ALOT.!
Sounds like you certainly know your stuff mate. I wish I was as clever.
Wish you were in the UK and I'd be straight over to you and pay you kindly for a check-up ;O)
Anyway, I have some reading to do and looking forward to it.
Thanks for your time today mate, appreciated.
In the meantime, do relays generally get pretty hot.? This is the one I mentioned a couple of posts ago.

Cheers bud.
Rob
 
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Sharkie1976

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Well, I've had a good look through the manual and the wiring diagrams.
I have managed to find out some info, but not really sure whether I'm on the right tracks or not (probably the latter, lol).
J271 ecu relay is Relay R1 under the hood in the upper fuse/relay holder.
J271 relates to fuse 23 (5amp) also in the upper holder (terminal 30).
J757 is Relay 4 & fuse 42 (5amp) also in the upper holder.
J271 & J317 is also connected via fuse 10 (5amp) in the lower holder.

So, how am I doing?? I don't mind if you have to tell me I'm doing crap, lol. It's my first attempt to try and work through this with no experience.
Couldn't seem to find anything as regards to relays and Terminal 15.
Hmmmmmm!!
CHeers,
Rob
 
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Sharkie1976

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Hey Jack.
Well, I have gained some knowledge, but unfortunately thats about all.
I have tested every fuse inside and outside of the car. Also removed every relay and tested with a 12volt supply whilst checking the continuity. All switches in the relays work fine.
I guess I should have checked the earths first, may be the next thing for me to check.
I am starting to lean towards it being a Carbon build up issue, which seems to be very common with Audi direct injection models, and does cause poor starting. I think it's down to the fact that the carbon absorbs the fuel on first starting, therefore a stumbling start. I may be wrong and I hope I am, as it costs between £450-£600 to get the carbon removed from intake valves/ports and inlet manifold.
When weather permits, I'm going to check the earths and then check if there is too much voltage drop on the battery when cranking the engine.
Would appreciate it if you could comment on what you think about the carbon buildup and my next steps.
Many thanks,
Rob
 
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Jack@European_Parts

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Well you did good so far with the absence of the auto-scan.

An auto-scan is always helpful with true logs............

So far nothing.:banghead:

Intakes do get clogged with carbon, and yes carbon acts as a sponge for cold starts.
Personally I doubt it is it for sporadic condition though.
 
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Sharkie1976

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Hey Jack.
Lol, Uwe kindly linked my auto scan on page 1, so it is theoretically there.
The only relays I haven't checked is the ones under the plenum chamber, where rain etc runs below the windscreen, and I believe 1 fuse also resides there. Cover is a bit of a pain to remove tho. I have also cleaned out the throttle and it did have deposits in there. Car started very well for 2 days, but now rough like before. Bloody car, lol.
 
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Sharkie1976

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Hey Guys.

It's been a while and I thought I'd update the thread with how I fixed the problem.
Ok, one day I came across a BMW forum and there were quite a few people complaining of the same/similar issue. They found that it was in fact Shell V-Power Nitro + (RON 99) causing starting issues.
I thought to myself I'd try changing fuel brand as from what I read, the higher the RON figure, the harder it is to combust.
Anyway, to cut a long story short, I ran the tank down low and filled with Esso Supreme 97 and hey presto 2 months down the line, I haven't had any more hard starts. It fires up so much better now.
I know of lots of people that swear by Sheel V-Power, and I thought it was a nice fuel, but my car just doesn't seem to like it at all. I have used it for over a year and have always had this starting issue.

Hope this helps somebody out there with a similar problem.
Regards,
Rob.
 
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seems similar to a bad check valve in the lpfp . it should make around 6.5 bar on low pressure. do output test on low pressure fuel pump with mechanical gauge in line its the black fuel line not blue. then shut off car and the fuel pressure should not loose more than 3 bar in 10 minutes. if so there is a leak. you can isolate the leak by clamping off the hose going to the engine and repeating the procedure to rule out a leaking fuel injector.
 
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