The_real_Svempa

My -97 A8 has almost 100k miles, I have owned it for a little over 3 months and around 4000 of these miles. It happened to me twice in the same day, after owning the car for a month, that it refused to start at the first attempt. It did start finally, after perhaps 40-50 tries where it sometimes would run for a second or two, then die, or just not give any signs of life. The battery is OK, so is the starter which turns well enough.

I suspected water in the gasoline, since at the time the tank was almost empty, so I put a quart of ethanol in the tank. Probably wrong diagnosis, since today the very same thing happened.

The car was parked at the supermarked, we had been doing some shopping and it had started with no trouble four times earlier the same day. It did start again, after a large number of attempts and also letting it rest for half an hour.

Only similarity is that the engine must have been "half hot", it had been parked for perhaps two hours in both cases. Also today is a rather cold day, air temperature similar to the day in March when I had the same problem.

Usually the car is parked for the day, or over night, between starting attempts and under these conditions the engine has always caught on the first attempt.

No error codes in storage, I have tested with the VAG-COM and there is nothing. No error codes at all in the time I have owned the car, except one that indicated an intermittent problem with the airbag front passenger seat sensor.

Could it be the immobilizer acting up? Or is it perhaps a failing fuel pump? Grateful for any tips and suggestions of procedures for finding this problem.<ul><li><a href="http://lundbybasket.net">I just love this game!</a></li></ul>

greenie

Could this be a "fuel soak issue" with the injectors? Do you smell gas after these attempts?

ryoung

which is not an uncommon problem on older, high mileage cars. Residual fuel pressure must still be &gt;44psi 10 minutes after shutting off the motor. If the regulator can't hold pressure, gasoline can vaporize in the fuel lines during the heat soak after shutting down, which results in hard staring. When the motor's cold after sitting overnight, even if residual pressure is zero, the car is not trying to run on vapor and will start fine.

The_real_Svempa

No gas smell inside car, outside it was difficult to tell - possibly a whiff. But on a big parking lot that could come from anywhere. On the other hand, I did notice the CAT lamp coming on momentarily a few times during starting attempts. Could this indicate unburnt fuel in the cat?

The_real_Svempa

Now that was an interesting thought. Maybe I am stupid, but next time I have this problem (I suppose there WILL be a next time) perhaps I should try unscrewing the fuel cap and put it back? Wouldn't that relieve pressure and fool the computer into another starting regime? Or am I just as ignorant as I feel?

ryoung

When the regulator leaks, liquid fuel in the lines between the regulator and the injectors leaks back into the fuel tank. The regulator "sees" the same fuel tank pressure on both it's inlet and outlet.

As long has you have normal fuel pressure when the car's running, the computer normally would have no idea what's happening. When the car sits for long periods, the residual fuel pressure usually goes to zero, but this isn't a problem with a cold motor. Your problem sounds more like the vapor lock you can get with carb motors.

The_real_Svempa

OK, thanks! How about this, then. Instead of immediately turning the key to start the engine, I just let the ignition be on for a few seconds, and THEN turn the key. In some other cars this gives the fuel pump a chance to build up pressure and makes it easier to start the car if the pressure regulator is leaking. Would this work for the A8?

Now, I am not suggesting this to avoid replacing the pressure regulator. I just want some indication that it really IS the pressure regulator that needs replacing. Instead of something else entirely, like fuel injectors or perhaps the fuel pump.

ryoung

if the fuel pump runs with ignition on but motor not running. I don't know, though, if this is the case with the A8.

skiracer

It is the case with the A8- I can hear the pump come on with ignition switch on.

The_real_Svempa

Thanks a lot all of you for the valuable help! So now I know that the likely reason for the difficulty in starting a "half-hot" A8 is a too swift pressure drop in the fuel system. Cause can be a defective pressure regulator (high probability) or leaking injectors, perhaps even some problem with the return valve in the fuel pump (if there is one which I don't know).

Perhaps I could start by replacing the pressure regulator first to see if it helps, and also add some injector cleaner to the gasoline a few times. I'm unsure whether these cleaning agents actually do any good, but it is worth a try anyway.