JSA3

Our S-7 has stumped the Audi tech experts.

Last summer, I jumped into the car and hit the start button. The starter cranked the engine just like it always does, but the engine wouldn't start. After trying this two times, I was getting desperate so I thought I would just mash the throttle to the floor to see if that would have any affect. It did have affect, the engine started with a bit of hesitation, then idled and revved normally.

This car is my wife's daily driver, so reliability is key. Took the car to the Audi dealership where the car has always been serviced. A day later, they called and said that two of the four oxygen sensors were faulty and need to be replaced. The two O2 sensors were replaced (one sensor on one bank and one on the other bank) and in road testing the car started and ran normally. We paid the four figure repair bill and went home.

One month later, my stranded wife called saying the car would again not start and was exhibiting the same non-starting behavior as before. I asked her to try again and this time hold the throttle to the floor like I had done in the past. It didn't work for her. I called Audi for suggestions and they gave me the name of their recommended towing company.

I drove over to where she and the car were stranded. Once I arrived, I got in, tried a normal start and as before all it would do was crank the engine over without starting. So, once again, I mashed the throttle to the floor, hit the starter button and the car started right up. We took the car directly to the Audi shop and dropped it off.

Nine days later, I got a call from the shop saying they were having a difficult time diagnosing the problem but they believed that the had discovered the issue. They had discovered that the fuel pressure between the fuel regulator and fuel rails would hold steady after turning the engine off, but the fuel pressure between the fuel pump and regulator would bleed down, pointing to a faulty fuel pump. They never mentioned to me what the fuel pressure readings were. Of course they did provide the four figure cost for replacing the fuel pump.

I reminded them that the starting issue the car was now having is identical to the starting issue we had the previous month. I asked if they were certain that replacing the fuel pump would fix the problem. The Service Advisor said they were confident.

I responded "great" because if I need to bring the car back in again with the same starting issue then Audi would be comping the repair costs. Audi decided to take another look at the car before releasing it to me. Some additional Audi Techs got involved and came back and said the fuel pump didn't need to be replaced as the " fuel pressure differentials" were not significant. They also said that the car wasn't throwing any codes that could provide any help diagnosing the problem.

The conversation ended with their current best guess diagnosis is the car had received some bad fuel.

Any ideas here on what's going on.....?

Avantly

You don't have a 4.2, you have a 4.0T. I'd post this question in the C7 forums.

wakkaluba

O² sensors rarely go broken. Especially if 2 are affected it is more than unlikely.
Did the car die on your wife while she was driving?

JSA3

No, it didn't die while she was driving. It simply wouldn't start.

wakkaluba

So to recap:

• The car cranks
• no MIL (engine light)
• no errors stored
• allegedly the engine starts up when hitting the throttle to the metal before cranking

My next step would be get a diagnosis device that can display the crank and cam signal or even better get an oscilloscope and back probe the sensors and gather the signals while cranking. Using a diagnosis device may display default signalling from the firmware instead of the real signal. Hyundai is known for that on the maf.
For some reason do many ECUs not report wonky signals from the cam shaft and crank shaft sensors but cut the fuel supply if the signals ain't right. Others simply switch from crank to cam shaft sensors and co-relate the position for the crank shaft.
I that issue before and it drove me nuts before I figured it out.