220SEb fuel pump pressure - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 03-05-2013, 02:50 PM Thread Starter
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220SEb fuel pump pressure

Having a frustrating problem with a 220SEb. Car sat for a while, obvious isues in fuel tank. Removed tank and had it coated, rebuilt fuel delivery pump, (have done more than 10), flushed lines, changed filter in canister. Car cranked and ran after about 15 seconds, drove it, ran good, idled good. Next day car cranked and ran for about 30 seconds, developed a lean miss and shut off, would not restart. After about 15 minutes same thing. Figured trash blocking rebuilt pump, took apart, no problem. Disconnected return line to tank and tested flow, which was good. Still same result. Disconnected metal fuel line to cold start valve and hooked up pressure gauge. Initial pressure 12 psi, drops off quickly to zero. Installed late model pump from C220, same pressure, same result. Blocking the return line partially, was able to raise pressure to about 40psi and car would continue to run. Talked to Gus and he said there were no pressure regulators in system, just dampners, pump takes what it needs out of "flow through". What's going on here?
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post #2 of 6 (permalink) Old 03-05-2013, 04:58 PM
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it drops off quickly to 0 because either the screen in tank is plugged , the screen in electric fuel pump is plugged , the main fuel filter under hood is plugged , that is about it .assuming pump is ok .this car will run on very low pressure a few psi like 2 to 3 will do it .when the screens on the suction side are plugged , usually the pump noise will change to a higher pitch . you are on the right track to test pressure at cold start valve .there is a pressure valve at the return line of inject pump that control the max pressure of system , 10 to 12 psi , it never goes bad .
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post #3 of 6 (permalink) Old 03-05-2013, 05:04 PM
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after checking , the 220 se does not use a fuel pressure regulating valve , so dont look for it .
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post #4 of 6 (permalink) Old 03-06-2013, 08:16 AM Thread Starter
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Question 220SEb fuel pressure.

While the elctric pump is running (key on) there is sufficient fuel returning to the tank as viewed through the sender hole. Plus you can hear the fuel running through the lines at the main filter in the front. I'm wondering if something is causing the fuel to aerate. When I take the filter down after the car shuts off, it is only half full of fuel. There are no fuel leaks. The tank is more than 3/4 full.
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post #5 of 6 (permalink) Old 03-06-2013, 02:26 PM Thread Starter
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Problem solved: Found return line in tank broken, i.e. no loger going to chamber around fuel screen. When tank was cleaned and coated it restricted flow into the chamber to such an extent that the pump would suck it dry. Without the return line flowing back into it, but instead just into the tank, the car starved for fuel once the chamber was empty. Once the car sat for a while, the fuel would work it's way into the chamber and it would start and run for a while, i.e. until the chamber was empty again. Now have to cut tank open, repair the return line and drill some small holes into the chamber so fuel will flow into it, just not so big that all the fuel will run out during cornering. Thanks for the guidance agillot!
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post #6 of 6 (permalink) Old 03-07-2013, 03:30 PM
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Wow, glad you finally figured this one out. It was a stress maker for you in your previous posts. I am unclear however if the recoating caused this, such as too much coating material clogged the return line, or was it literally broken off somewhere either from age or the recoating process? Again, congrats!

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