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  #1  
Old 10-10-2019, 07:39 PM
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'72 250 fuel pump concern

Haven't been around here for a while - car has been running ok until just the past week. Was having some vacuum leak problems and I replaced one of my climate control vacuum pods under the dash...

Car was having trouble idling, without keeping the gas pedal pressed. Now the car won't start - cranks fine but no start. Pulled the fuel supply lines from the Zenith carbs and cranked - no gas. Pulled the filter from the Pierburg mechanical pump and no gas...

I replaced the pump many years ago - do they just go bad? Any other reason I might not be getting fuel to the carbs?

ryan

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Old 10-10-2019, 08:25 PM
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Quote:
Originally Posted by rgnprof View Post
Pulled the fuel supply lines from the Zenith carbs and cranked - no gas. Pulled the filter from the Pierburg mechanical pump and no gas...
I replaced the pump many years ago - do they just go bad? Any other reason I might not be getting fuel to the carbs?

1) Tank is empty.

2) Flex line between chassis & pump has a hole; sucking air.

3) Line between tank & flex line is clogged.

4) Screen in tank is clogged.

5) Pump has failed [which may or may not be why you replaced the pump many years ago!]
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  #3  
Old 10-11-2019, 08:51 AM
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Thanks for the reply!

Tank is not empty and I'm pretty sure the pump was bad when I replaced it 15 years ago as the car ran fine after a new pump.

Not sure about 2, 3 and 4...I've probably got 10 gallons in the tank right now so I'm not sure how to go about draining that much fuel to check on the screen...I'll just have to crawl under and look for issues 2 & 3...
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1984 300D
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1986 560SL
1991 300CE
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  #4  
Old 10-11-2019, 03:03 PM
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Id second the screen pull line from tank before pump. See what flow you get. Wear safety gear be ready to place back on. After determination is made
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Old 10-12-2019, 06:44 PM
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Installed a brand new Meyle fuel pump and it made no difference - do I have to prime this new pump somehow???...would like to pull the strainer in bottom of tank but have to figure out a way to drain the gas.

I have checked the lines as best I could - just eyeballing them...don't see anything obvious.
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1984 300D
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1986 560SL
1991 300CE
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  #6  
Old 10-22-2019, 12:28 PM
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Quote:
Originally Posted by rgnprof View Post
Installed a brand new Meyle fuel pump and it made no difference - do I have to prime this new pump somehow???...would like to pull the strainer in bottom of tank but have to figure out a way to drain the gas.

I have checked the lines as best I could - just eyeballing them...don't see anything obvious.
When I need to empty a fuel tank I just get some clear plastic hose and siphon it out. Get two five gallon gas cans, about ten feet of clear 3/8 inch hose and set aside a few hours to let it drain.

I use clear hose because that way I cab suck the gasoline right up to my mouth and can see it coming. Then I place a thumb over the end of the hose to hold the vacuum. Lower the end of the hose to a level below that of the tank by putting the gas can on it's side and pushing the hose in while it is almost on the ground. Then stand the can up and watch the gas flow.

Flow rate is about one gallon per hour with diesel. I am not sure about gasoline. Perhaps one gallon in 30 minutes?

And you will not be able to see the gas flowing if it is clean. But you will not see any air pockets if the line is flowing. You can also hear the gas flowing into the car if everything else is quite.

You can also buy a siphon pump but I have tried them and never had a lot of luck with them working as they should.
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Old 10-22-2019, 05:15 PM
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You really need to empty tank. Pull a line get a big enough container and let it go. Go from top if needed so it can be controlled better. You have to clear out those lines

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