Car starts but won't stay running

Hello I have a 89 Mercedes 190e. The car stays running and will drive but after so long starts acting like it’s starving for fuel. I have spark and nothing wrong with fuel filter but when tested there was no pressure what’s odd is the fuel pump was tested and it works fine all the lines have been cleared I’m stumped what else can I check

Have you checked the accumulator?

Do you have 1 fuel pump or 2?

Does the pressure drop off rapidly after you shut off the engine?

2 both have been tested and the car just shudders and dies and then after it dies it won’t start

I have I have even replaced it

I believe there is an external check valve for your fuel pumps

Have you replaced them?

Where would it be and what would it look like I’m doing this for my bf been working on this for almost a month now

The check valve looks like this

By the way, the fuel pump relays on these cars have been known to be very problematic

The relay might be located in the engine bay, near the firewall

I’m just throwing some stuff out there

Thanks if that don’t work I shall be back

A bad inertial cut off switch is a possibility. It’s designed to shut the fuel pump off in the event of an accident. There’s also a check valve in the tank that’s designed to seal the output line in the event of a rollover. Perhaps that’s somehow hung up in its chamber. Both are designed to prevent an accident from becoming a conflagration worthy of World News Tonight.

It should be a CIS car so the aggravation factor will go way up…

Those fuel pumps can certainly be a fine one minute, failed the next, fine again type of situation.
If it’s the original pumps then I’m surprised they’ve held up this long. CIS works under much higher pressures than a “normal” injection system so the pumps take a bit of a beating.

Ok how would I get into the tank to fix it without cuttinh a hole

The fuel pumps are NOT in the tank. The fuel pumps are under the car. They’ll be near the differential housing

I was referring to the check valve in the tank

The check valve is also not in the tank

It is attached to the external fuel pumps