Help needed: '88 Mercedes 230 GE fuel issues

[M_G]

Hi all,
I am experiencing some problems with my '88 Mercedes 230 GE. The truck has stayed for three years. I started it, it starts and idles OK but after few minutes the pump starts to work louder, the idle goes rough and the engine does not want to pick up RPM's. If I start driving immediatly after starting the engine, it will drive fine for the first few minutes and then - the power goes away and the engine stalls. I changed the fuel pump with a known good working one and put a new fuel filter - no sucses.
What else could I check/repair?

[ncc.1701]

How the car was stored?
Regular gas is good for 1 month or so
Premium good for 3-4 month over this period - add gas stabilizer

Also full tank will prevent humidity and therefore rust in the gas tank

[benhogan]

sounds like a fuel issue.

pump out the fuel in the tank. you will notice that it is ORANGE not clear.

[M_G]

Thanks guys!!!
The truck was stored bad, very bad, actually it wasn't stored it was abandoned . The tank was empty. When I changed the fuel filter I noticed the gasoline was orange. I put half tank new fuel in.
benhogan, it is definatelly fuel issue.
What is the next suggestion?

[benhogan]

you can attempt to dilute the orange fuel with good fuel and burn it off.

personally, i would pump it out completely either from the filler neck or via the fuel pump.

you can hot wire the pump where it pumps continuously to the disconnected fuel line in the engine bay.

get rid of the orange and you will be fine

[M_G]

Well, thats the problem, there is no more any orange fuel in, the tank was empty and I filled it up with about 25 liters of new fuel thinking that this will solve the problem - it didn't.