When the car runs it does really well but on occasion it will not start, it will turn over but will not fire. After several attempts it may or may not start. It may also go for a week or two and do fine and then all of a sudden it will not start. I have installed a new crank position sensor and a new battery and still same problem. Any help would be appreciated.

 

Any other OBD codes being thrown by the ECU? I had some intermittent non-start issues on my D2 A8L about 5 years ago that turned out to be a fuel pump going out.

 

No, I thought a bout the fuel pump but it runs perfect when it starts and it actually cranks different when it does not start as opposed to when it does which leads me to believe it is a sensor or a module going bad or having a loose connection

 

Could be. Go ahead and get the OBD codes from the ECU. It will probably tell you what is malfunctioning.

 

First thing I would check is the vehicles battery. The weather is changing in most of the country and when the temperature changes, car batteries love to go dead. We have already had four vehicles towed in with dead batteries since the weather hit 40 degrees in Central New Jersey. One day they are good, the next day they are bad. You would need a DVOM to check battery voltage before attempting to start the vehicle and then when you are trying to start the vehicle. You need the battery at 12.6 volts at least and above 10.5 volts when trying to start the engine. If those number are lower than that, you need a new battery or batteries.

As per the post before mine, you want to see if there are any fault codes in 01 ECU. If there are fault codes, that will give you a path of what to check. It could tell you the battery had a low voltage situation, or that the G40 Engine Speed Sensor is acting up. If there are no fault codes, you are going to want to check for spark and fuel injection pulse when the vehicle is cranking over but not starting. It is a pain in the butt to get to the Fuel Injector on the engine, probably have to back pin the ECU connector.

If all those items check out good. You need to check fuel pressure when the vehicle is not starting. The in-tank pumps should be at like 60 psi plus when trying to start the vehicle. If you do not have fuel pressure, then you need to check power and ground supply to the pumps. If that test is past, vehicle is going to need new fuel pumps. Yup both of them.

 

New battery
New engine speed sensor
No Codes
I would believe that a fuel pump would act up while driving as well. I have had them go out in other vehicles and when they went they went.
I believe this is an electrical issue when it starts it runs perfect

 

What type of scan tool are you using?