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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 50097
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1977 Mercedes Benz 450SL: fuel line..hoses..the fuel pump..fuel filter

Resolved Question:

I have a 1977 Mercedes Benz 450SL that i just replaced all the fuel line hoses at the fuel pump and fuel filter. After the reassembly the car would not start. Fuel was at the pump and going into the filter but not getting to the engine. I removed the line that goes from the pump to the filter. (banjo style hose fittings on both ends) As i was inspecting the banjo bolt that comes off the fuel pump i noticed that the bolt had a pressure valve in it. I moved the banjo end of the hose to the outside of the bolt and reassembled. The car started right up and idled just fine. The problem now is that when i turn the car off and it sits for a few minutes it wont start. If i pour a little fuel into the throttle body it starts right up and continues to run fine. It seems that the fuel is draing back from the engine? Im wondering if i still have the hose from the fuel pump to the filter hooked up wrong?
Submitted: 5 years ago.
Category: Mercedes
Expert:  Marty replied 5 years ago.

HiCustomer could you possibly upload a picture of your pump and fuel lines?

 

Marty

Customer: replied 5 years ago.
Hi, I have been trying to send a picture but i cannot find out how to do it. It says click on the picture of a tree above the reply box, i do not see any tree.
Expert:  Marty replied 5 years ago.
Ok, I know it can be difficult sometimes. I think your browser settings affect the toolbar. If you contact customer service they can help you. Chances are you have everything connected correctly. Was this not a problem before you replaced the hoses?

Customer: replied 5 years ago.
graphic The car was running fine before i changed the hoses.
Expert:  Marty replied 5 years ago.
We're almost there but your picture didn't insert. Can you try again?
Customer: replied 5 years ago.
graphic
Expert:  Marty replied 5 years ago.
Ok, that looks correct at the rear. Tell me what the car is doing now?
Customer: replied 5 years ago.
Hi, It will start if i put a little fuel directly into the throttle body and it will continue to run just fine. When i shut it off and it sits for more than a couple of minutes it will not start again unless i again prime the throttle body with fuel. Thanks Bob
Expert:  Marty replied 5 years ago.
Hi Bob, did this all happen as a direct result of replacing the hoses in the rear?
Customer: replied 5 years ago.
Yes, The car started just fine prior to replaceing the hoses. I keep thinking that it has something to do with that banjo bolt pressure check valve that goes to the fuel pump. It's like as soon as you shut the car down it is loosing the prime to the engine. But with a electric fuel pump i dont see how this can happen? I would think that once the the ignition was turned on the pump would pressurize the system. Bob
Expert:  Marty replied 5 years ago.
That's correct Bob, when you crank the motor fuel pressure should build pretty quickly. Since the car runs fine I don't think you have anything put together wrong. I would go ahead and replace the fuel pump check valve and see if that helps. Another common problem is a leaking fuel accumulator which mounts in front of the pump and filter. You can check it by removing and plugging the small hose that connects to the back of the accumulator and starting the car. If fuel continuously flows or drips from the pipe on the accumulator is needs to be replaced. All of these problems would cause extending cranking but not a no start. Perhaps if you cranked it longer it would start on it's own. I wouldn't expect you to have to crank it for more than 10 seconds or so. From your picture I see the main hose coming down from the tank going into the fuel damper, the lower hose from the fuel damper going into the pump, the outlet of the pump going into the fuel filter and the outlet of the filter going to the motor. The smaller upper hose from the damper goes around to the back of the fuel accumulator. If that's what you have I'd replace the check valve and check the accumulator. Let me know if you have any questions.

Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 50097
Experience: Bosch Certified Master Tech. Over 35 years experience.
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