Hello everyone. I need help with this as fast as humanly possible, I am hoping someone sees this and can give me some pointers.

My 2007 Q7 3.6 is cranking but not starting. This is the second time this happens (see below) but this time the car seems like it won't start on its own like before. Here are more details:
- VAG-COM does not display any codes when it just cranks and fails
- One out of 3-4 tries it does start but idles very rough and I can rev it up to 4000 RPMs but it immediately dies - in this case I do get a bunch of VAG-COM codes (misfires and intermittent signals for various sensors, none in the Engine module). The battery discharges quickly so I have to keep it hooked up to my friend's vehicle, I am assuming that's why I get the intermittent signals.
- I did change one of the fuel pump relays with no improvement
- I could not hook up a fuel pressure gauge to test the actual fuel pressure (cannot find the proper fitting). However, I disconnected the fuel line by the engine and turning the key to position 1 or or attempting to start the vehicle does make it spit gas at fairly high pressure. I understand I need to get a reading of the actual fuel pressure as both too low or too high pressure can make the injectors not open, but does this rule out the fuel filter?
- I cannot locate the engine speed sensor (crankshaft position sensor) G28. The fact that there are no codes thrown indicates this could be the culprit, correct? I purchased an AllData subscription and they do not have any information about the G28 sensor
- Could this be because of clogged injectors? I tend to think not, as this happened all of a sudden with no prior signs and it doesn't seem isolated to only a few of the injectors/cylinders
- This is only the second time this happens, both during extremely cold days. The first time the car just started and after a period of rough idling it began running smoothly after it spit a lot of black water out of the exhaust. I then thought the moisture buildup in the engine/exhaust froze and caused this. I now tend to think that was not the case.

I know this is a lot to process but any help would be appreciated. I found almost no information about fuel pump and crankshaft position sensor issues related to the Q7.

Thank you!
George

 

Here's an update: I think I was able to read the fuel pressure (Engine/Measuring Blocks/Group 103) and it is pretty steady at 7 bar. This seems to be normal, correct? Does it mean this leaves the G28 sensor or clogged injectors as contenders?

Thanks again

 

With the risk of being persistent, here are additional details:
- the car has new coil packs installed by the dealer under a recall about 3-4 months ago as well as brand new spark plugs and air filter. I installed new spark plugs and the new air filter 3 days ago when this first happened
- I have noticed a lot of white smoke lately and it doesn't seem to be from coolant (coolant level unchanged and there is no milky stuff in the oil)
- I put some Heet into the tank. Should I double up (any risk of damage with less than 1/2 the tank full?) or use Seafoam at the throttle body? Maybe both?

Thanks again!

 

How did you end up going?

I've had very similar issues with my Q7 3.0 TDI.

It's been happening on and off for about a month now, it would crank but not fire up, it would shake like it did but nothing. The engine light would stay on (emission light) only when it misfires, but no codes have come up. I've had the fuel tank cleaned, changed filters and a service, all was looking good till it happened again the others night... I'm thinking it's the fuel injector or a sensor somewhere??? Really hard without a code

 

I realize that this happened a fairly long time ago... Can you share with us how it was repaired?

I have a similar situation - no codes, won't start or fire at all. I'm looking for a tee so that I can check fuel pressure, but I do know that I have 'some' fuel pressure. New fully charged battery.

2007 Audi Q7 with 3.6l engine