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Problem with a 1996 C220 Mercedes

This car “Mercy” whistles like a slow quail unpredictably but almost every day. I understand that this may be a vacuum leak.
Sometimes when it is pouring rain, she won’t start unless I open and close the gas cap. Now she has a new trick. When I slow down and stop for a stop sign or a red light she frequently dies but always (maybe I shouldn’t say this) restarts. Money is scarce but I have a brother who is willing to fix it with my help. He thinks we need to start with the pump in or near the gas tank. I bought a repair manual CD about 5 years ago but I never could hook up with the online manual so I cannot use it. We need to know where the pump is and how to go under the dashboard and look for where the singing originates without setting off the airbags. Also, when I totally fill the tank, gas leaks. Another problem is a broken O2 sensor, but I don’t want to repair it until I have to for inspection since my mileage is double what it was before. By the way, my ABS and check engine lights are on. What do you suggest? Thank you.
(Ms.) Dale from Memphis

You have two fuel sending units in the tank. They are NOT the pump. They are accessed by removing the back seat. Then there is a pump underneath the car, near the right rear tire. It’s under a black cover, along with the fuel filter.
You may have a problem with the evap system. Do you continue pumping gas after the nozzle clicks off? That is a big no-no.

If you want to buy parts, use these guys. They’re more expensive than, though.

The check engine light is probably on because of the O2 sensor you mentioned.
The ABS light may be caused by a faulty stop lamp switch. Common on Benzes.
All of your AC mode doors are vacuum actuated. One of the actuators probably has a leaking diaphragm. That would explain the “singing”