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1976 mercedes: I know you advise I get a fuel pressure test done…

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Hello, i asked some questions...
Hello, i asked some questions of you last night about the fuel problem with my 1976 mercedes 450 slc. I have a few more questions. I know you advise I get a fuel pressure test done. What i want to try at least first is to replace the fuel filter. see the car started when i got it a year ago. it only has 78,000 orig miles and the previous owner only drove it on occaison. I'm thinking when i put fuel cleaner additive to the gas that all the sludge that's built up may be trapped in the filter. I would at least like to change that first, simply test. my question is, i bought the filter today, and a little piece of paper inside says warning, fuel system pressurized filter release fuel system pressure before servicing. How do I do this? And what is the order in which the fuel flow from the tank? like tank to fuel pump, to fuel filter, etc down the line. I want to know the order in which fuel reaches the carburator.
Submitted: 8 years ago.Category: Mercedes
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Answered in 41 minutes by:
6/13/2010
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 55,280
Experience: Bosch Certified Master Tech. Over 35 years experience.
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eurotec :

Hi, the warning is a general precaution for all cars when opening the fuel system. If the key has not been turned on overnight there will be no fuel pressure. Any pressure in the system will be relieved when you loosen the nut on the line to the filter. Just crack it loose and let any pressure bleed off before you loosen it more but if the car has sat overnight there will be little or no pressure in the system. Fuel flows from the tank into the fuel damper before the pump then into the big inlet hose at the pump then out of the pump into the filter.

Customer:

Hello Eurotech. sorry i have been away from the computer. yesterdsay i asked this question and while waiting had to leave so I left this open till i could come home today and finish so I can send you some money for answering my questions. My next question would be... when i take off the fuel filter, is there a way to check if the fuel pump is working or clogged while i have the filter off? hopefully eliminating another possibilty? What should i expect when i take off the fuel filter? gas to come pouring out? What else can i check to see if its clogged or checked when i have the filter off and how do i check these things if there are?

eurotec :

Sorry I was away also. You will get a steady flow of fuel through the fuel pump and out the open lines when you remove the filter. I usually just let it drip into a pan and be quick about changing the filter. You don't want to run the pump with the fuel lines open at the back. I'd just replace the filter first and if you still have problems a fuel pressure and volume test should be performed at the motor. If you want to check the screen in the fuel tank for being clogged you could remove the big hose that goes to the pump and let it drain into a container. Fuel will come rushing out of the hose at a steady rate if the screen is clear. As far as the filter you are replacing you can check it for blockage by trying to blow through it in the direction of flow. If you can blow through it without and difficulty it is fine. Attach a piece of hose to the filter and blow into the hose, don't inhale the gas fumes!

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