Bought my 98 ml320 two years ago which the guy told me he just changed the fuel pump. "it would drive about 5 minutes and die with check engine light" he said. Last night I had cruise set at 59 (hypermileing) and i had on and off sputtering, pulled over and idled perfectly. Checked under the hood, looked at stuff, nothing leaking MAF looked fine, ran code scanner (I carry one) nothing, no check engine light no codes. started and ran fine for another five minutes started like it was running out of fuel again, but still idled fine. shut off and restarted to have the same problem. then I called for a tow two miles from home. While waiting still no codes and didn't even want to restart, just kept cranking. I stoped it after about 5 real seconds. I decided to turn the key a few times and noticed i don't hear the fuel pump priming at all. checked the fuse (good), switched the relay for another (still no luck). Got it home and it instantly started up, still no codes. But in my driveway I'm not hearing it prime every time I turn the key and when I do it sounds like its less time than normal. You guys think it's the F/P? possibly a loose wire to the F/P? Isn't there normally a code for a bad F/P or is that about the one thing that won't throw a code? Haven't tore up backseat to test power yet. Any thoughts?
Alex, Carmichael CA

He changed the pump, how about the filters? Could be worth testing fuel pressure. It also isn't unheard of to have a flaky fuel pump relay and/or wiring to the pump.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

You can access the wiring at left rear wheel well area ther is a 5 pole connector attached at left side frame, may need to remove fender liner to get a better shot at connection point, its just below filter on frame

Thank you all very much for the prompt replies (Diseasel300, and nulu.) Over the last week I have been tinkering and figured it all out just now. but to start the next day car started and ran fine, fuel gauge was showing over 1/4 tank still. Checked fuel pressure at the rail and it was literally running on ZERO Psi. Not a joke and actually idled nicely. So just to check the gauge I poured in 2 gallons from a jerry can I had and the fuel gauge went up and the pressure gauge climbed to 49 quickly. Either way the pressure was flickering all over between 48-51 so continued pressure test. It did not change with/without vacuum and failed the 30 minute test dropping to 20 psi so I changed the regulator/filter immediately since it was clearly in early stages of failing. While back there I noticed the F/P connector on the fame had been unclipped and half the pins looked unpluggedish, so that was fixed. as for the filter being changed with the pump 2 years ago by the previous owner it was date stamped 11/13 which is around when the F/P was done before I bought it. Either way it immediately worked like a brand new car with a lot better mpg (computer reading) than before. the filter/regulator was clearly going shot anyway.
[B]To the main problem[B] The last day Ive seen the gas gauge not go below that same spot again, so I fueled up and the gauge went to zero with no reserve light, full tank. Ive tried all the ways people online are saying to reset the instrument cluster such as pulling some fuses and disconnecting the F/P connector on the frame while key in position 2 no success. I finally found success in resetting it! Disconnect the battery for 30sec and while disconnected touch both battery cables together to discharge the modules. (old trick I learned for 90's cars passing smog, although valueless today) Started the car (full tank) and gauge was still on zero, (got depressed) Shook the car a little and the gauge slowly climbed, Drove it around for less than 5 min, gauge would not climb above 3/4. Parked the car, turned all the way off and back to position 2 after 1 second and the gauge read perfectly right below full. I have never seen it so spot on! now I just need to make sure it will read when down at reserve again.