What would be the reason for what appears to be two fuel pumps on a 1986 420 sel. Does it take two pumps to get enough gas from tank to engine?
Thanks

Durability. Two smaller pumps working together don't have to work as hard, and if one fails, the other will keep the car going well enough to limp to a repair shop. If you only have one pump and it fails, where do you think you will be?

I like the dual pump idea, because I hate the idea of depending on an electric pump to begin with (being a diesel lover at heart)....so at least its a bit more reliable.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The two fuel pumps in my 560SL are in series (the output of Pump 1 feeds the input of Pump 2) to boost the fuel pressure rather than using a single, higher capacity pump. I don't know if the car will run at all with one of those pumps out as I have never experienced a failure. May be worth disconnecting one as an experiment.

I suspect your setup is similar.

That would be nice to know. I figured it was for redundancy, too. That sounds like German engineering to me.

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" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

In my experience, my E320 would not run with one of the pumps bad. It quit 2 times on me and had to have it towed,,, one time for each pump.

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95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

Instead of using a dual stage pump, they use two pump. But the secound pump requires pressure from the first, so the car wil not run on a single pump..they are in SERIES.

__________________
A Dalton

I can vouch for that. I got stranded once on the side of a motorway in my old 86 420SEL. One of the electrical terminals detached from one of the pumps due to corrosion. Deader than a doornail.

__________________
93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

So, is it pretty safe to assume that if one goes out, the other one should probably be replaced at the same time?

__________________
" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

Not always...the trick to keeping pumps working well is to change the filter regularly..a partially clogged filter allows the car to run , but it puts a restriction burden/strain on the pumps.
And on some chassis , the new replacement is a single pump in place of the dual set-up.

__________________
A Dalton

Whose coat is this jacket?

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Peach Parts W124.128 User Group.

80 280SL
85 300SD
87 300TD
92 300D 2.5 Turbo
92 300TE 4Matic

Great....I thought it offered redundancy. Stupid gas cars.....if those pumps die.....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

One of the pumps on my 560SEC would overheat and shut off while driving, due to an almost completely clogged fuel filter. The car would all of the sudden have no power, and would idle very roughly. Not sure if that was because it was only running on one pump, or because of the clogged filter. Guess it doesn't really matter? lol. Replaced both pumps and filter, and all was fine. Although a while after I sold it, the new owner told me the fuel filter had clogged again. So change those filters regularly!

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

"they are in SERIES."


Something about the word series that makes me wanna argue....... (inside joke).


-tp

I was once told that the pumps are serial, to provide greater pressure (power) to the fuel injectors.

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Thanks for the help
Bill Fisher

'86 560SL (186K) - Now a 'classic' : Registered as an Historic Vehicle
02 E430 in the stable
'14 LS460 (Lexus)
- - - - -
'95 E420 (198K) found a new home
'99 E320 (80K) (gave it's life for me as we hit a bumper)
'95 E420 (231K) Sold to a happy buyer, new to Mercedes
'90 300E (65K) Sold to an Mercedes Lover
'92 190E (215K) - retired to the salvage yard
'93 500SEL (214K) - Moved to another family, still runs like a young pup