2000 Audi A4 problem starting when engine is hot

Check for spark the next time it wont start.

Vehicles operate by the same principle; basic troubleshooting procedure applies to most cars.

Step 1 - Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If all fuses test ok continue to the next step.

Step 2 - To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) and the fuses test ok a trouble code scan is needed to identify any system trouble. Use a simple scanner tool to retrieve trouble codes and see if they relate to the specific problem, like a crank angle sensor failure code. If the trouble code present does not pertain to the immediate problem like an EVAP code ignore it until a later time, after the car is running. The reason we repair non-related codes after the engine is running is because sometime false codes can be triggered by the engine not running. Once the engine is running again the code present might cycle and turn itself off. You might say "if the engine doesn't run shouldn't it have a trouble code?" Sometimes conditions occur that will not be detected by the computer, example: if the fuel pump fails the computer cannot detect the failure, so the engine doesn't start and the computer thinks everything is ok with no codes. If no trouble codes are present proceed to the next step.

Step 3 - The spark plugs in your engine are used to ignite the compressed fuel air mixture. If the condition of the spark plugs are fouled by excessive fuel or carbon the engine will not start, backfire or run rough. Remove all spark plugs to inspect their condition. Please use this spark plug condition reference guide to see how the spark plugs are operating.

Step 4 - Determine if the engine has compression, this can be done a number of ways but the most complete method is to perform a compression check. Remove the spark plugs and perform a compression test on one cylinder. If one cylinder has compression then the remaining cylinders usually will be close to the same. Crank the engine over about 5 seconds, normal compression readings should be between 125 psi and 160 psi on each cylinder. If no or little compression exists additional tests will be needed. The most common reason for an engine to lose compression is a timing belt or timing chain failure. If low or no compression exists remove the oil fill cap and observe camshaft rotation when the engine is cranked over. If no rotation exists the timing belt or chain has failed. If your engine has a timing belt and you cannot see the camshaft easily remove the upper bolts to the timing cover and gain visual access to the belt, recheck cam rotation by cranking the engine over. Sometimes a timing belt or chain can jump causing the camshaft to lose correlation with the crankshaft and therefore causing low compression. The best test for this condition is to remove the timing belt/chain cover and inspect timing marks. If the compression is ok proceed to next step.

Step 5 - Test the ignition system output, ignition systems can vary in configuration but operate on the same principal. Ignition systems can consist of a coil, pick up coil, crank angle sensor, cam angle sensor, spark plugs, spark plug wires, distributor cap, ignition rotor and a distributor and any variations of these components. An ignition coil is a voltage stepper coil that transforms a low voltage (12 volts) signal into tens of thousands of volts needed to jump the gap of the spark plug. This coil is activated by an ignition module triggered by using the camshaft/crankshaft angle sensor; timing is adjusted by the ECM (computer).