My 300E fuel woes continue. Now its chewing through fuel pumps like they are going out of fashion.

Last weekend I dropped the fuel tank, cleared out a ridiculous amount of rust and water crap and put it back, together with a new outlet screen and hose. I fitted a new pump and filter. Yesyerday it ran well for about a hour round town in various journeys. I fillled the tank to around 3/4 full last night and went to bed, fingers crossed that everything was fixed.

This morning, i start her up and the engine fires for about 30 seconds, then the fuel pump starts making a loud buzzing noise and the engine refuses to run, even to idle.

This is the third new Bosch fuel pump that has trashed out on me. The first, about three weeks ago, didn't deliver sufficient pressure out of the box, so I took it back to the shop and changed it. Two weeks ago, before I cleaned the tank, I replaced the charcoal filter, which was rusted through and full of water thanks to a poorly routed windshield drain hose, and fitted another new pump and fuel filter. The pump ran for about 20 minutes of CO/idle testing until it stopped pumping enough to let the engine idle.

Anyone have any idea what's going on? Fuel Pump Relay appears to be functioning correctly in that it switches on and off like its supposed to. Fuel lines have been blown out and there's no obstructuions. Have pressure at the fuel cap. Tank filter screen is new. Outlet hose to pump is new. Hose from pump to filter is new.

Don't know what to do. Can't keeping putting new pumps on, its getting expensive. The pump that came with the car doesn't pump up to spec but it seems to work, so that's going back on again tonight.

New or replaced parts in this round of madness:

Fuel filter
Fuel distributor (secondhand but less than 1 yr old)
Fuel pressure regulator
Charcoal filter on fuel return line
Check valve (at tank)
Tank output filter screen and outlet hose
New injectors
Fuel pump(s)

Any help or suggestions much appreciated.

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1987 300e manual 250,000 km (sold)

we're thinking it might be the check valve on the pump. Turns out my mechanic swapped them when he fitted the newest pump (absolutely not because he'd scratched the first one and no way could he send it back to the distributor as a failed item like that, no no not at all)

will find out first thing tomorrow morning.

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1987 300e manual 250,000 km (sold)

You need to perform a current and voltage check at the pump. The relay maybe clicking but the contacts may be burnt. MB has a complete testing procedure for the pumps. What you are experiencing is not normal.
Good luck.

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Auto Zentral Ltd.

I'd say that there's a good chance input screens, filters, valves are still becoming clogged, starving the pump for fuel.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

replaced the check valve. seems to be OK now, but I've said that before. I'll see in a couple of days

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1987 300e manual 250,000 km (sold)