What would cause my 1998 Mercedes S320 not to start.

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their are some electrical issues with s320 throttle valve electric failure --coil pack failure -- check fuses and relays then check battery and connections and try to start with boost if starts check and test battery and alternator --and check the wiring connections for loose , frayed , damaged ,and corrosion the following link are some of the problems acossiated with your vehicle
Newest Problem Reports for the 1999 Mercedes Benz S320

The tapping could have been from the overheating. Check all the fluids. As far as the pedal never heard that one. The only thing I can think of is if the heat was affecting the slave. Causing the fluid to boil. This would cause lose of pedal.

brake light is prob a bad bulb somewhere , totally seperate from the running problem , get your fuel pressure checked on the fuel rail not sure but should be about 40 50 lbs if not then your fuel pump is prob bad and it is in the tank

Possible bad master cylinder or air trapped in the system. Take it to a brake shop and have a power bleeding done on the system. Other possible causes could be low brake pads that have little sensors built into them that have to be replaced at same time as the pads.

Hi there:EPC - Electronic Power Control

If its like some other models is doesnt have a traditional accelerator, its drive by wire. Possibly pumping the pedal as you try to start is causing that. First off check for air getting into the fuel line.

Hope this helps.

CDs...DVDs started in '03

Try this,sitting still,running,in park,hit the brake really quick and hard,
is the pedal ok? Then hit the pedal very softly slowly,and seeif it just fades to the floor .If this is the case the master cylinder is bad.
Also,keep in mind this vehicle had a twin cylinder,if you have complete failure of either end of the vehicle,the other half will still work but the pedal is very low,as you describe.
Check the fluid level,if only 1/2 the res.is full,that's the deal.

have the alternator checked, the voltage regulator maybe going out

remove master cylinder cap and fill with brake fluid.
start at back passengers rear , helper pushes brake pedal 3 times. you or whoever losens zert with. small wrench. bleeds air pedal pushed to floor. repeat .
switch to driver rear brake . repeat couple times
then move to front and do same, starting also with passenger side first.
make sure master is full of fluid
hope that helps