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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53608
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Mercedes-Benz 300 TE wagon reg Mercedes 300 TE wagon regular problem;low

Customer Question

Mercedes 300 TE wagon regular
problem;low fuel pump pressure
tested visual : disconnected fuel line into fule inj. dist body.....set into bottle....turn IG to on.........easy going pressure flow........then crancked expecting super flow 10 lb + major increase flow....however no change....same easy going flow......checked both pumps: both HUM few seconds and vibrate when touched when turn ign to ON since pumps actuate....discarding fuel pump relay........
next suspects.....low volt pumps.....semi clogged filter.....bad accumulator ??
Submitted: 5 years ago.
Category: Mercedes
Expert:  Marty replied 5 years ago.
Hi Albert, a plugged filter or bad accumulator can cause this but I would suspect low flow to the pumps from the fuel tank. I'd check the fuel flow to the pumps by removing the fuel line from the tank.
Customer: replied 5 years ago.

ok....but how can one check flow from tank coming into pump #1 which is located right forward next to tank....??? dont have any testing equipment.....

is it possible exit orifice inside tank semi clogged ??? do you know if there is filter

prior fuel entering pump #1 ??

gas tank is about 1/2 filled.... in principle, if one would stick coat hanger back into tank, through exit that feeds in to pump #1...should it run freely into tank...and theoretically clear any debris at exit point ???


i was thinking prior change fuel filter....some kind test to pumps make sure are operating at max voltage....../?


Expert:  Marty replied 5 years ago.
I've never seen low voltage to the pumps but you could check it at the pumps with a voltmeter. There is a filter screen (pictured) inside the fuel tank at the main hose outlet. It's a gravity feed to the first pump. If you remove the hose the fuel should pour out from the tank. Has this car been sitting unused for a long time?

Marty and 2 other Mercedes Specialists are ready to help you
Customer: replied 5 years ago.

yes car sitting around 2 yrs waiting my daughter get her license...she got few months its her get around town car.....I did start up once in a while.....

she started driving regular last 2 months...until it she parked and would not start again a week ago......

with this info you still suspect gas tank filter ??


about pump voltage test...was sort of empirical it bseems pumps either good or bad.....nothing in between ??




Expert:  Marty replied 5 years ago.
If the car has sat for two years you may be dealing with cleaning or replacing the tank, the pumps, the filter, the fuel distributor and the injectors. The CIS injection system does not hold up well with old fuel in the system. You need to start at the tank and work forward. Step one is to make sure that you have good flow to the pumps.
Customer: replied 5 years ago.

hello eurotec

finally been able get back to MB problem....

latest........did look for tank filter...seems no access at tank exit point ..

was able check fuel flow after pumps prior filter...

upon contact ON regulra flow...upon cranck good increase flow...

visually for sure no clog nor debri in this portion of fuel folw...

so by default took fule filter compare with new one...

original filter when blowing with mouth, almost no flow....

new filter when blow air with mouth goes thru minor resistant.........

so I said...yes found culprit....

checked again visual at entry point fuel inj distri...looking good....


thinking all ready to go.......i figured would help start up if sprayed fuel in each piston chamber.........that would fire up engine right away creating suction to facilitate fuel reach injectors, etc


removed all spark plugs.....checked two for visual spark with few crancks...put plugs back..........

then pretty much shocking ... started engine assuming would fire up inmediate

since have spark, fuel/air...

not even a puff !!!

rotates...will not start.......I expected few puff from fuel sprayed in to pistons ???

any ideas at this point ???



Customer: replied 5 years ago.
Relist: Answer quality.
Answer to general and now a bit late...
Expert:  Marty replied 5 years ago.
Hi, sorry I have been in and out the last few days and missed your reply. Do you still need help with this?