# Help me diagnose my intermittent hard/no-start!!!



## dasfinc (May 11, 2007)

So my 2001 Audi AllRoad (2.7t Quattro A6 Avant basically) is more or less fully re-assembled, and I am trying to wrap up its issues before the weather gets too nasty.

One issue it has is it seemingly randomly has a hard or no start, where it just cranks and cranks but doesn't start. Sometimes it seems that a dab of the throttle seems to help, and it seems to happen commonly while low on gas, or shortly after a fill-up. It seems to happen more commonly on cold start, but happens while still warm as well on occasion.

Today it full on stalled out at a stop light, and again as parking while nearly completely empty.

The CELs it has are all emission control related, which would not point this at a sensor failure. I also don't think it's wiring or power related, especially after it cutting out today at a light while super low on fuel, and again as I came to a stop parking. 

It has not cut out while under load, or experience any kind of miss.

Leaves me thinking Fuel Pressure Regulator, Filter, or Pump.

The filter I'll try tackling tomorrow as its cheap insurance and I have no idea when it was last done, and I will take a look at the pump since it has a fairly easy to access panel, but as its so randomly intermittent, and doesn't have issues under Load AND I hear it prime and it's not making any loud or 'bad' noises it makes me think FPR since that's tied to Vacuum, which may be related to some of my emission CELs?

Thoughts? Things to test/check?


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## Junkyarddawg (Dec 5, 2013)

I had the same symptoms on my 01 A6 2.7T. At around 180K the car first started misfiring on #4 intermittently but wouldn't throw a code, I had to look at the misfire recognition measuring blocks with VCDS to figure out which cylinder was missing. Shortly after that the engine would ,mysteriously and randomly, just stall out and would not restart. Every time that would happen I would find that the fuel pump was getting 12 volts but not running. I checked the relay and all the connections and no faults were found, I removed the fuel pump and tested it on the bench and it would run when I put 12 volts on it, every time. I put the pump back in the tank and it worked for about 2 days and then stopped working again. Finally I just put a Walbro 255lph pump in the tank and the car has never ran this good since I have owned it. What I determined during the diagnosis is that when the fuel delivery falls off on these engines air pockets will develop is the fuel rail and it seems to affect the front cylinders first. Have actually measured rail pressure that was in specification but when I discharged the pressure it was at least 50% air pressure! Like the pump is cavitating somehow.
Hope this information helps....


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## dasfinc (May 11, 2007)

Junkyarddawg said:


> I had the same symptoms on my 01 A6 2.7T. At around 180K the car first started misfiring on #4 intermittently but wouldn't throw a code, I had to look at the misfire recognition measuring blocks with VCDS to figure out which cylinder was missing. Shortly after that the engine would ,mysteriously and randomly, just stall out and would not restart. Every time that would happen I would find that the fuel pump was getting 12 volts but not running. I checked the relay and all the connections and no faults were found, I removed the fuel pump and tested it on the bench and it would run when I put 12 volts on it, every time. I put the pump back in the tank and it worked for about 2 days and then stopped working again. Finally I just put a Walbro 255lph pump in the tank and the car has never ran this good since I have owned it. What I determined during the diagnosis is that when the fuel delivery falls off on these engines air pockets will develop is the fuel rail and it seems to affect the front cylinders first. Have actually measured rail pressure that was in specification but when I discharged the pressure it was at least 50% air pressure! Like the pump is cavitating somehow.
> Hope this information helps....


Where did you order your Walbro from? And was it just a matter of mounting the pump in the assembly, or was there any kind modding/tuning needed to run the Walbro?


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## dasfinc (May 11, 2007)

The intermittent turning itself issue was resolved with a new crankshaft position sensor. Cost $70, took about 3 hours to do due to the location being Nestled up against the hot side of the turbo.


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