Hello,

My A4 has starting problems, the problem is that it needs to crank over for about 10 seconds to start at last, when it has sat for about 30 minutes or more. It does not depend, is the engine warm or not, when the engine is cold, then it is more harder to start, t. I have tried to change coolant sensor, fuel filter, have tried 3 different fuel pumps and replaced the fuel pressure valve. What is very strange, is that sometimes it starts perfectly for about one month, sometimes for a week or some days and then suddenly the problem is back, i have no more ideas, what to check for next! I have also read fault codes some time ago and it is showing one fault: 561 Mixture regulation adaption value, upper additive adaption limit threshold exceeded, permanent

 

Any codes for the crank position sensor?

When these are faulty they can effect starting.

Jason

 

It do not remember, did it have the cranks position sensor fault at the first fault code reading, all faults were deleted and i did the next day another fault code reading and only the 561 Mixture regulation adaption value fault was back, but maybe i should try to replace the crankshaft sensor? It is strange, that sometimes it works for a pretty long time and then is failing again, i have tried also to check all the connections, that i was capable of.

 

Could definitely be the crank sensor. It's responsible for picking up the crank location and properly adjusting timing and fueling for starting. So it would be plausible.

Jason

 

I've actually had the same problem ever since I had my fuel pump replaced. That's why I jumped in this thread. I was going to tell you that my Audi guy said that this is a result of a bad diaphragm in the fuel pump itself, causing the fuel to drain back into the tank. That's why it doesn't start right up anymore, but if you've replaced you fuel pump too, we both might have the same issue. Something other than what's been suggested.

I have brand new crank, cam, coolant temp and speed sensors in my car, so we can rule those out (if we have the same problem - which it sounds like we do).

I told my Audi guy I could try to turn it over and over and the starter would just keep spinning w/o any signs of the engine wanting to turn over. He told me that's because our cars have a 2 second (electrical) prime before start, so if the gas has made it's way all the way back to the tank, you can let the engine turn and turn and turn, but it'll never start (since the priming is electrical and not enough to carry the needed fuel to the engine if it's drained all the way back to the tank).

Here's what I do now: Before I start the car, I put the key in the "ON" position, wait a couple seconds, then try to start it. If it doesn't turn over immediately, I turn it back off and right back on again and that always seems to work for me. It's usually the worst when it's cold (which makes the explanation sound reasonable to me).

Try that, then let me know if it works for you. Crank it over once for just a second or two, then try again immediately after. If it happens when it's cold, drive it until it warms up, then stop somewhere (like a gas station), let it sit for five minutes or less. If you have the same issue I have, then it should fire right back up, but even when it's hot, you can still experience this problem, depending on how fast the fuel is back-flowing and how long you let the car sit (like letting it sit for 20 minutes or so).

Try that out and let me know your results, because if you experience the same issue as me and you've had multiple pumps replaced, then I doubt it's the pump and we need to look elsewhere.

 

Usually the fuel pump starts working, when the the engine is rotating but i have tried it that way, that i try to turn over it just for a sec, then i hear that the fuel pump is working for about 5 sec, the fuel should come up then? But this do not make any difference, the car still wont start better. Also, when i disconnect the fuel backflow pipe from the fuel pump, then when i am cranking over the engine, then it starts pumping fuel almost immediately, that should show, that the fuel has not flowed to the fuel tank? I have tried to start it for very different ways, but nothing will change, sometimes, it seems that a little throttle will help.
Also when the pump would be dead, then would it some times work? At first when this problem has started occuring, then i leaved the car sitting for about one week and when i tried to start it after one week, then it just started immediately

I think that i will try to change the cam sensor and lets see is it helping. Maybe it could also be just a bad connection between the cam shaft connector?

 

I'll be interested in seeing what you find.