380sl low system pressure, noisy fuel pump
09-15-2013, 01:55 PM
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Jetta TDI, BMW 323i
380sl low system pressure, noisy fuel pump
OK, I've been somewhat stumped by this one and no longer have access to shop information that I used to have when I was a mechanic. I'm working on my uncle's 380sl- I believe it's a 1986. I've searched and searched but been unable to find these exact symptoms on any forum or troubleshooting chart. I don't have access to a decent fuel system diagram and this is more complex than the CIS cars I've worked on in the past.
The fuel pump was replaced not long ago- it was bad from sitting too long with old fuel in the system. I flushed out all the lines without pumping bad fuel to the fuel distributor so once the tank was cleaned and the pump replaced everything appeared that it would be fine.
The car starts and idles nicely when cold. As it heats up it runs worse and worse till it won't keep running. I figured that's simple, right? Control pressure regulator!
I was wrong. The control pressure and system pressure drop lower the longer the car runs. As the car warms up the fuel pump gets louder and louder. It's apparent that something in the system is creating a blockage that gets worse as the car warms up. When I put a gauge at the pump (in the back, before the line) the fuel pressure went well above 100 psi. When the pressure is that high the pump makes an awful racket.
I've blown out lines, checked for dirt or blockage in the lines in and out of the fuel distributor, and checked for blockages at the two pressure regulators and control pressure regulator.
I'm familiar with the more simple BMW, VW and Volvo CIS, CIS-Lambda and CIS-E injected cars. I'm confused by the Mercedes dual-pressure regulator setup. I would very much like to fix this for my uncle- he's a good guy and the car is useless at the moment.
Can anyone suggest anything from the symptoms I've listed? Thanks for reading if you got this far!
Jamie
The fuel pump was replaced not long ago- it was bad from sitting too long with old fuel in the system. I flushed out all the lines without pumping bad fuel to the fuel distributor so once the tank was cleaned and the pump replaced everything appeared that it would be fine.
The car starts and idles nicely when cold. As it heats up it runs worse and worse till it won't keep running. I figured that's simple, right? Control pressure regulator!
I was wrong. The control pressure and system pressure drop lower the longer the car runs. As the car warms up the fuel pump gets louder and louder. It's apparent that something in the system is creating a blockage that gets worse as the car warms up. When I put a gauge at the pump (in the back, before the line) the fuel pressure went well above 100 psi. When the pressure is that high the pump makes an awful racket.
I've blown out lines, checked for dirt or blockage in the lines in and out of the fuel distributor, and checked for blockages at the two pressure regulators and control pressure regulator.
I'm familiar with the more simple BMW, VW and Volvo CIS, CIS-Lambda and CIS-E injected cars. I'm confused by the Mercedes dual-pressure regulator setup. I would very much like to fix this for my uncle- he's a good guy and the car is useless at the moment.
Can anyone suggest anything from the symptoms I've listed? Thanks for reading if you got this far!
Jamie
09-21-2013, 11:53 AM
#2
Junior Member
OK, I've been somewhat stumped by this one and no longer have access to shop information that I used to have when I was a mechanic. I'm working on my uncle's 380sl- I believe it's a 1986. I've searched and searched but been unable to find these exact symptoms on any forum or troubleshooting chart. I don't have access to a decent fuel system diagram and this is more complex than the CIS cars I've worked on in the past.
The fuel pump was replaced not long ago- it was bad from sitting too long with old fuel in the system. I flushed out all the lines without pumping bad fuel to the fuel distributor so once the tank was cleaned and the pump replaced everything appeared that it would be fine.
The car starts and idles nicely when cold. As it heats up it runs worse and worse till it won't keep running. I figured that's simple, right? Control pressure regulator!
I was wrong. The control pressure and system pressure drop lower the longer the car runs. As the car warms up the fuel pump gets louder and louder. It's apparent that something in the system is creating a blockage that gets worse as the car warms up. When I put a gauge at the pump (in the back, before the line) the fuel pressure went well above 100 psi. When the pressure is that high the pump makes an awful racket.
I've blown out lines, checked for dirt or blockage in the lines in and out of the fuel distributor, and checked for blockages at the two pressure regulators and control pressure regulator.
I'm familiar with the more simple BMW, VW and Volvo CIS, CIS-Lambda and CIS-E injected cars. I'm confused by the Mercedes dual-pressure regulator setup. I would very much like to fix this for my uncle- he's a good guy and the car is useless at the moment.
Can anyone suggest anything from the symptoms I've listed? Thanks for reading if you got this far!
Jamie
The fuel pump was replaced not long ago- it was bad from sitting too long with old fuel in the system. I flushed out all the lines without pumping bad fuel to the fuel distributor so once the tank was cleaned and the pump replaced everything appeared that it would be fine.
The car starts and idles nicely when cold. As it heats up it runs worse and worse till it won't keep running. I figured that's simple, right? Control pressure regulator!
I was wrong. The control pressure and system pressure drop lower the longer the car runs. As the car warms up the fuel pump gets louder and louder. It's apparent that something in the system is creating a blockage that gets worse as the car warms up. When I put a gauge at the pump (in the back, before the line) the fuel pressure went well above 100 psi. When the pressure is that high the pump makes an awful racket.
I've blown out lines, checked for dirt or blockage in the lines in and out of the fuel distributor, and checked for blockages at the two pressure regulators and control pressure regulator.
I'm familiar with the more simple BMW, VW and Volvo CIS, CIS-Lambda and CIS-E injected cars. I'm confused by the Mercedes dual-pressure regulator setup. I would very much like to fix this for my uncle- he's a good guy and the car is useless at the moment.
Can anyone suggest anything from the symptoms I've listed? Thanks for reading if you got this far!
Jamie
Are you seeing all of this while in idle? Or running it on the road?
Just a shot in the dark here, maybe an overload to the pump? A sustained surge would give you a psi jump, while killing it at the same time!
Ryan
PS To anyone asking for advise, Id like to see more videos or even audio posted along with the questions. Im very much a look and listen problem solver. Just a thought.
Last edited by RyanRichter; 09-21-2013 at 11:56 AM. Reason: Hungover
