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sprinkles08
sprinkles08, ASE Certified Technician
Category: Australia Car
Satisfied Customers: 21570
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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2006 Audi Q7 3.0 TDI - start issue - first start of day 2-3

Customer Question

2006 Audi Q7 3.0 TDI - start issue
- first start of day 2-3 5 second cranks (or 1 15-20 second crank) blows white smoke, then perfect
- subsequent starts pretty good all day
- sometimes doesn't want to crank first time when warm after 4-6 min after shutdown. Seems like very high resistance - one or no cranks. Then key it second time and no problem
- Same as last point occurs when really heat soaked - 1H+ run time. Try starting within 5 minutes of heat soaked run gives no crank / very high resistance of some sort.
- New battery, ammeter fine, starter cranking good speed. freshly serviced.
Suspecting 10 bar return or starter motor - thoughts ?
Submitted: 10 months ago.
Category: Australia Car
Customer: replied 10 months ago.
That's the 10 bar fuel pressure retention I was refering to - on the return side of the common rail.Seems to me like for the cold starts, the fuel is draining away so takes a while to crank up pressure...
and for the heat soaked starts / few min after shutdown starts same sort of deal - almost like there is fuel in the cylinder so when I go to start it is pre - igniting, or encountering high compression but is then fine for second keying. I have also heard that starter motors get high resistance with heat soak...... hoping this was a common set of symptoms that lead straight to a component. Audi checking it in 2 days time, so want the gross error check from you guys. Bonus pay and cudos if you get it right !
Expert:  sprinkles08 replied 10 months ago.

Hello and welcome to JustAnswer!

It does sound as if you may have one or more injectors leaking. Leaking injectors will cause the long crank time and smoke on startup and can also cause the cranking issue. The affected cylinders may be hydrolocking from excessive fuel in them.

It's possible the slow ranking is unrelated also. A failing starter may be the cause of the slow cranking, they will often give issues when hot. The engine c an be turned by hand with a ratchet to see if it's excessively hard to turn at that time. If not then the cables can be voltage drop tested and the starter condemned if the cables and connections are ok.

If the slow cranking started at the same time as the rest of the problems then odds are it's related, and I expect the problem is with one or more injectors.

Customer: replied 10 months ago.
Thanks. Put it into Audi today. Their diagnosis was a .75 volt drop across the chassis to engine and probable starter motor. $1500 replacement.
I'm sceptical. Put my multimeter on positive to engine and there is zero loss. Plus, for the other 10 starts a day there is no issue - so how would that support the starter motor theory ? Bit pissed off that they didn't specifically test the 10bar switch or the injectors like I asked them to - and just went straight for 'replace starter motor'.
Really don't know what to do next other than pay another mechanic to do what he is f**king told and test the injectors and return line pressure ! Very reluctant to throw $1500 at a diagnosis that does not support all symptoms.
Expert:  sprinkles08 replied 10 months ago.

The starter could cause slow cranking but that wouldn't explain the other issues. It's possible that you have more than one problem going on at the same time though.

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