WHY 2 FUEL PUMPS
 

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? :D

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.

fuel pumps
 

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.

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.

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.

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.

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

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.

Whose coat is this jacket?

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

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!

"they are in SERIES."


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


-tp

Give me power - scottie, give me power
 

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