help required - Q7 3.0 TDI BUG - late starting

[talhaizhar]

Dear All,

Frustrated and tired, i need help in diagnosing the exact problem with late starting (and sometimes never starting) of my 2007 Q7 3.0 TDI with BUG Engine.*


On different diagnostics and advices, I*have*already*replaced the following;

- Fuel Pump
- Throttle Body
- Both intake manifolds
- Battery
- Glow plugs

The problem is bit funny sometimes. It would start fine when cold and rested for few days. The cranking would feel bit hard and stucky but the car would start in few seconds.*


However, with engine mildly hot and car started again, the cranking is smooth but would go on and on and the car wouldn't start, unless when coupled with another battery and that also after a long cranking (with thick plume of white smoke, probably due to unburned diesel during long cranking). This problem is persisting from quite sometime now and has aggravated over the period of time. It has done 65K kilometers and have been kept with utmost care and timely maintenance.


However when the car is fully hot, it would start again with ease and with a smooth cranking.


The car is otherwise very healthy, very good engine and responses and drives like a charm. No alarms on VCDS also.


So once gain, when the car is *

- Very Cold - Starts fine with a hard/stucky cranking

- Mid Hot (or when left alone after running for few hours to a day) - Wont start with very long cranking

- Very Hot - Starts fine with smooth cranking

Now, after recent diagnostics at dealership, i was informed of a compression loss in one of the cylinder (cyl 6 to be precise with a reading of 9 - whatever unit it is) whilst all other cylinders are showing a healthy reading of 18. Bit difficult to digest and solution is a complete over haul of upper block only (if i get lucky). Again nothing on VCDS.


Frankly, i have lost the trust in those diagnostics and a major difficulty is that Audi in my country doesn't deals in Diesel models and this one was a personal import. So no wise mechanics with personal experience and knowledge base.


Anybody out there with similar experience and suggestions? Please help. I have a ross tech VCDS and can run tests and provide more info if required.


Thank you in Advance.*

[joe1303l]

I had similar intermittent starting issues with a 2006 BUG engine, a new Starter solved it for me, fires up almost instantly.
Might be worth getting yours checked out.

[talhaizhar]

I had similar intermittent starting issues with a 2006 BUG engine, a new Starter solved it for me, fires up almost instantly.
Might be worth getting yours checked out.
Thankyou Joe

Was your intermittent starting issue random (can happen in any condition) or like mine ( always starts when very cold or very hot BUT not when left for few hours to a day after driving).

Sorry for describing it like this but I hope you would understand what I mean to say.

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[joe1303l]

Mine was definitely intermittent as it would generally but not always "struggle" to start if it had not been started for a few hours or even days.
By "struggle", it would crank for maybe 10-20 seconds before starting, the resultant start would then give a cloud of grey smoke.
On the times it started properly, it would start after just a few sceonds and no smoke.
The occasions when it started properly were either when the car was started recently(less than maybe 3hrs) or totally random, outside temperature didn't make any noticeable difference.
To clarify, it never actually failed to start but the battery often went close to going to flat. I started carrying jump leads in the boot out of fear of being stranded. The battery was replaced and even subsequently tested twice in attempt to solve the problem.
My local Audi Dealer couldn't find anything wrong even when they kept it overnight a few timed to cold start it. As it got worse over the last 2 years, they eventually suggested either injectors or the starter.
As injectors were €€€€, I went with replacing the starter but they were clear that they could guarantee either would fix the problem.
It starts instantly since and I regret not having replaced the starter 2 years ago as it had really bugged me.

[talhaizhar]

Mine was definitely intermittent as it would generally but not always "struggle" to start if it had not been started for a few hours or even days.
By "struggle", it would crank for maybe 10-20 seconds before starting, the resultant start would then give a cloud of grey smoke.
On the times it started properly, it would start after just a few sceonds and no smoke.
The occasions when it started properly were either when the car was started recently(less than maybe 3hrs) or totally random, outside temperature didn't make any noticeable difference.
To clarify, it never actually failed to start but the battery often went close to going to flat. I started carrying jump leads in the boot out of fear of being stranded. The battery was replaced and even subsequently tested twice in attempt to solve the problem.
My local Audi Dealer couldn't find anything wrong even when they kept it overnight a few timed to cold start it. As it got worse over the last 2 years, they eventually suggested either injectors or the starter.
As injectors were €€€€, I went with replacing the starter but they were clear that they could guarantee either would fix the problem.
It starts instantly since and I regret not having replaced the starter 2 years ago as it had really bugged me.
thanks so much and I will go with starter motor replacement.

Fingers crossed.

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[joe1303l]

Best of luck with it.
FYI they allowed 4-5 hrs Labour for it from memory.