Audi Repair: 1996 Audi A4 Wont Start, fuel delivery systems, crankshaft sensor

Question
Hi, thank you for taking the time to read this.  I went to dinner with a friend tonight, and when we went to drive away in the car.  It wouldn't start up!  The starter engaged and spun the engine with it's normal enthusiasm.  But turn and turn the engine there was no combustion.  I looked under the hood and couldn't figure it out by staring at the engine.  I couldn't find the fuse box... so I just got a ride home...  I am planning on going back to the car in the morning to try and diagnose the problem.  I feel like the issue may lie with the fuses, a relay, or perhaps the fuel pump has quit.  This problem has come on suddenly with no warning.  

Can you give me advice on how to test ignition and fuel delivery systems to pinpoint the problem?  I don't want to buy and replace parts in an experimental fashion, I will if that is what it takes, though.

Thank you again for your time and any help you can provide!

Answer
Hi, There could be many reasons for a no-start.  First thing to check is that you are getting a spark, so take a spare plug with you and check for a spark when you get to the car.  You will typically need another person to look or crank the engine, make sure the plug is plugged in well and makes a good connection on the metal (ground) of the engine, secondly you need pulses from the crankshaft sensor to switch on the fuel pump.  If the fuel pump is not being activated, I would suspect the crank sensor first.  You can check the fuel pump relay too, as it can sometimes fail.  Usually these problems are a loose connection or a simple part like a relay, and I agree with you that throwing expensive parts at a problem like this is not wise.  Get the codes read out from the computer; your answer may be there already for you...  Let me know,  Jan