2.7T won't start

[eejit]

I'm cross posting this here 'cause no response in the A6 forum and it's an S4 engine :S - sorry if that's not cool:

Hello, first post, hope this is the right sub-forum, etc...

I've recently got myself a 2002 A6 Avant, 2.7T Quattro Manual (about 2 months ago). Prior to this I've had Mondeo's and Volvos and have been able to do work on them myself (so I'm quite disappointed to find out that there's no Haynes Manual for the C5 A6!).

Recently it's been taken longer to start, and having come back from a holiday is now completely failing to start. The starting process sounds absolutely normal, it just will not take. A quick google throws up this thread from here, which seems to match my symptoms. I have read the OBD and it is showing an EVAP flow rate incorrect code, so I have three questions:

1) Could the EVAP code cause the car not to start? It seems unlikely from googling this.
2) Would a water temperature sensor create a fault code? I have an Autel EU702 for reading more codes than a standard OBD but haven't had the chance to use it yet as the car's in another city.
3) Is there any other common causes I could have a look for?

Many thanks.

And my update today:

OK so I've read all the codes I can with the Autel EU702, it comes up with the following codes:

17861 - P1453: Exhaust Gas Temp Sensor 1 (G235): Open or short to plus.
17865 - P1457: Exhaust Gas Temp Sensor 2 (G236): Open or short to plus.
16825 - P0441: EVAP Emission Control Sys: Incorrect Flow
18010 - P1602: Power Supply Terminal 30: Voltage too low

I'm guessing if my Water Temperature Sensor was faulty I would have a code for it? So I'm going to have to assume that one of these codes is causing my start issue. I can write off the P0441 code, as a bit of Google-Fu would suggest that it won't cause the car not to start. Again, Googling P1453 and P1457 would suggest that if those stop working the car would just assume that they were at the maximum temperature and overfuel, again not causing the car to not start. Can anyone offer an alternative opinion on that?

That would leave me with just P1602. Now the battery is definitely dead - I connected a power pack to it today to crank it, it was definitely only cranking off the power pack, and when I unplugged the power pack I watched the needle drop from 8-10V to zero in the space of about 3 seconds. I assumed that like the OP of the thread I linked to in my first post, that's because of having to keep cranking it to get the engine to start and that getting steadily worse, but now I'm wondering if the battery was dying before and that was causing it to be progressively worse at starting? My issues with starting the car started about a two weeks before it failed to start entirely. Any thoughts?

 

[eejit]

Have now replaced the battery and still won't start, so it wasn't the battery. Have unplugged the temp sensor and tried to start it and it won't, so I guess it's not the sensor that's faulty? There was some corrosion around there though.

I also cleared all the fault codes in the hope that it would leave a single fault code for whatever's causing the car not to start, but now there's just no fault codes. What's that about?

 

[aragorn]

Maybe its the crank sensor?

Your codes wont come back until the engines running.

 

[eejit]

Cheers for the suggestion. So would the crank sensor being dud not cause a fault code? I know when the camshaft position sensor went in my old Mondeo TDCi, it had a fault code that was active even without getting the engine to start. Is there anyway to verify that it's the crank sensor, other than just replacing and seeing if it starts? I'm keen not to just throw money at the problem if I can, even if a sensor is

 

[eejit]

Additionally. I had to get a tow from a mate to get my car back to my flat tonight. Turning the wheel with the engine off appears to have caused a power steering fluid leak - from the top of the reservoir. What sort of damage may I have caused? What should I look out for? Or will it just be a case of getting a new seal?

 

[aragorn]

I think these systems dont give any codes for the crank sensor, they just assume the engine isnt turning and thus theres no fault.

You can use VCDS to view the engine RPM when cranking to see if it registers anything. If it does you can rule the crank sensor out.


As for the leak, probably some air in the system or its overfilled if its leaking from the reservoir. I wouldnt worry too much about it.

 

[eejit]

Cheers for the suggestion. I don't have a VCDS, and my Autel resets from the live data feed if you try to crank the engine so I can't try that. I just bought the sensor because it's not massively expensive. Currently in the process of replacing it, which is not exactly easy! Not a lot of space in that engine bay and everything I want to get to seems to be behind something else.

I'm going to replace the sensor as I have it anyway, but from more googling, it seems that the fuel pump is another thing to check. It's difficult to check this on your own, but when turning the ignition it did not sound like it was priming. I'm going to get someone to have a listen to it later on tonight while I turn the key. If it happens that it's not making any noise, what should I check before replacing the pump? Fuses and relays?

 

[eejit]

A couple of things I noticed today:

This hose doesn't seat well on whatever this canister is:

This is on the left side at the back as you look at the engine, the similar one on the right is well connected. Would this cause any issues?

And this sensor doesn't appear to be plugged into anything, it's just hanging loose. It's connected to the positive battery lead. Looks like it's maybe just an ambient temp sensor or something so I imagine not too important?

I'd like to know where to plug it back in though.

 

[aragorn]

first one is EGR or SAI or something

No idea what the second part is, is there a number on it? Looks like half of a solenoid valve or something.

 

[S4_dan]

Have you tried starting the car with a booster pack at all?

Longshot, but I did this on my 2.7TT S4. IT FRIED THE ECU! God knows why, as I had started many cars using booster chargers/ packs before. When I tried starting the car, the ECU got a spike and it burnt some of the track on the PCB! Car would crank over but not fire at all.
Luckily, I sourced another ECU quickly and cheap too!

Worth checking the ECU. I could smell the 'burnt' track before I even opened the ECU up to inspect it.

Like I say, it's a longshot, but could be worth checking as it is free and easy.

My issue turned out to be my battery was shot and that is what caused the spike as it didn't absorb any of the charge whilst starting the car using a booster pack.

 

[eejit]

Have you tried starting the car with a booster pack at all?

Longshot, but I did this on my 2.7TT S4. IT FRIED THE ECU! God knows why, as I had started many cars using booster chargers/ packs before. When I tried starting the car, the ECU got a spike and it burnt some of the track on the PCB! Car would crank over but not fire at all.
Luckily, I sourced another ECU quickly and cheap too!

Worth checking the ECU. I could smell the 'burnt' track before I even opened the ECU up to inspect it.

Like I say, it's a longshot, but could be worth checking as it is free and easy.

My issue turned out to be my battery was shot and that is what caused the spike as it didn't absorb any of the charge whilst starting the car using a booster pack.

I did try to jump it with a Jump Starting thingmy, I will look into this if my current angle of attack doesn't work.

 

[eejit]

I have fitted a new Crank Angle Sensor. That didn't fix my non-start issue. I now think it's the fuel pump - no sound from the pump on cranking the engine and there's a voltage across pins 1 and 4 at the connector so this should rule out any electrical issues i.e. fuses and relays, correct?

I've bought a new fuel pump anyway as if it fixes the issue it'll still be cheaper overall than the garage but I think this is the last thing I'll do before giving it up and taking it to a garage for a diagnosis.

 

[S4_dan]

Couldn't you try a direct 12v to the pump to see if it run before purchasing a new one?

My fuel pump wouldn't run with the ECU being burnt out, as the track was shot where the main power comes into the ECU board, so nothing was working that was ECU controlled.

Hope it's not the ECU, I was lucky and had my key code for reprogramming the immobiliser/ecu to the car/key

 

[eejit]

Couldn't you try a direct 12v to the pump to see if it run before purchasing a new one?

My fuel pump wouldn't run with the ECU being burnt out, as the track was shot where the main power comes into the ECU board, so nothing was working that was ECU controlled.

Hope it's not the ECU, I was lucky and had my key code for reprogramming the immobiliser/ecu to the car/key

Surely if the ECU was burnt out there wouldn't be voltage - since it wouldn't be telling the fuel pump to pump? Not sure by what means I would stick 12v into the pump either. Not saying it's not possible, just that I don't have the tools/components to do it.

 

[aragorn]

if your defo getting 12v at the pump and its not pumping, then it does suggest the pump is dead...

 

[eejit]

It was indeed the fuel pump, my Audi is once again working. Thanks to everyone who pitched in with suggestions and advice. I ended up following this guide for fuel pump replacement.

I would note however that while he recommends disconnecting the return line under the lid of the pump, if you have an OEM style like for like replacement pump it is easier to unclip the end of the return line in at the basket, as the replacement pump will come with this line attached. There's a kind of bracket that a couple of lines are connected to that if you feel underneath with your fingers you can unclip. Looks like this when you get it out:

Now that my car's working again though, the stereo won't switch on. More stuff to do!

 

[S4_dan]

Glad you found the cause in the end. A relatively easy fix.