Author Topic: Fuel Pump Assembly  (Read 306 times)

John Moore Sr

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  • Location: Washington NC
Re: Fuel Pump Assembly
« Reply #15 on: 15 September 2020, 06:20 AM »
Joel. I personally would stay with the one line accumulator.  It's more simple and cost effective rather than purchasing more parts (hoses), plus the 2 line unit appears to cost more than the single line version. A compromised or ruptured diaphragm simply means the part is BAD and will not function. You don't want that.  As far as the 126 numbered damper is concerned, again, like I related to you previously, is the factory service replacement that was available at the time it was obviously replaced on your car. Another possibility is that your complete fuel pump assembly was replaced with one from a 126 chassis car or at the very least the damper was.  By the way, does your fuel pump run? I ask this because of the debris in the damper illustrated in your photo could have been drawn into the pump rotor and jammed it. If so your are going to need a pump. If your pump will run, I would certainly flush it with fresh fuel before it was connected to the filter and accumulator. I would also remove the check valve during this to insure no debris fouls it up. A word of caution if you do this....keep in mind the pump delivers a high volume of fuel when running. Use extreme caution and connect a hose from pump down inside a suitable container to catch and contain the fuel flow.  While your pump assembly is removed you can test the pump to determine if it will run by using jumper wires to a battery. Remove the pump from the bracket, drain it thoroughly, and have it and the battery away from the car, any fuel or fuel residue. Also hold pump in hand when you apply voltage to it. The motor is very torquey and can go skating across the floor or workbench. Make sure the polarity is correct as well.   Oh by the way, I checked in a stash of parts today and found an original 116 numbered  damper.  I had it backwards. The 116 part is larger diameter than the 126 replacement. I'm going to clean it up, photograph it and post it here for all to see.  Be careful and I hope this helps .   
« Last Edit: 15 September 2020, 05:56 PM by John Moore Sr »
1972 350SLC Euro Parts car, 1974 350SL Euro 3.5 V8 4 speed, 1978 450SLC Euro. 1979 6.9 #4630 1979 6.9 #7003 Parts Car, 1980 450SLC Parts car, 1985 380SL...and once had 1975 6.9 #142 until JuNIOR commandeered it.

revilla

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  • Location: Aix-en-Provence, France
Re: Fuel Pump Assembly
« Reply #16 on: 16 September 2020, 01:37 AM »
Hi
The setup shown in the pics its just fine. I wouldn’t add complexity to your problem by doing a conversion. I would leave that alone.
Your accumulator looks indeed old externally, perhaps due to salty roads in a previous life. It doesn’t mean however its internal functionality is compromised. You need to test it as suggested. Simply blow air at low pressure first on one end. Air shouldn’t come the other end. If it does, the diaphragm is broken which puts you in the path of replacing it. They still available, although pricey.  You should increase the test pressure gradually up to 3-4 bars. Why? Because sometimes depending on the failure mode of the diaphragm it can hold low pressure just fine. If at low pressure you have air flowing the other end, test’s over. But you don’t want to start at 3 bars directly as you my break it (if weak).
Testing the pump performance as suggested is also a good idea. 1 liter in 30 seconds per spec.
Once the fuel pump/filter/etc package disassembled, it’s a good opportunity to test both in/out lines by blowing air ALWAYS in the direction engine->fuel tank, obviously with the hoses disconnected at the back. This test should give you a rough idea of their internal condition.
Damper: 126 part is ok for later models. It won’t make any difference. As suggested I would simply clean the junk inside and reinstall.
Good luck
Robert
Robert
W116 1977 280SEL & 1979 280SE

John Moore Sr

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  • W116 and R/C107 Enthusiast
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Re: Fuel Pump Assembly
« Reply #17 on: 18 September 2020, 04:44 AM »
RE: Dampers.  As I related in earlier post, attached photos of 116 and 126 fuel dampers.  116 first then 126.  JM Sr
1972 350SLC Euro Parts car, 1974 350SL Euro 3.5 V8 4 speed, 1978 450SLC Euro. 1979 6.9 #4630 1979 6.9 #7003 Parts Car, 1980 450SLC Parts car, 1985 380SL...and once had 1975 6.9 #142 until JuNIOR commandeered it.