So I just repaired a loss of fuel pressure issue, 95 E320. It had lost fuel pressure and I was so surprised to find both fuel pumps dead because I assumed it required both to sustain adequate pressure. I bought one replacement pump thinking I would test and identify the bad one..replace that one only..

The reason mechanics replace BOTH pumps is that when you lose fuel pressure, one pump has failed already and then you finally lost the remaining pump and both are dead..Its a reduncancy design..And perhaps when one fails the other is soon overworked and failure results..

Anyone care to coment?

Ive never noticed this anywhere in the info. , other than that two per car required, is noted regarding fuel pumps..And Id say if you have no fuel pressure and the circuit is active..yep, two needed.

I see you can drive on one but ordering another ASAP..

What was the mileage on the pumps?
I changed them on my wife's daily drive at 350K Km (217K miles) as preventative maintenance.
I took one apart and there was still some brush remaining but a lot of commutator wear so I'm glad that I invested in new ones.
If one fails from high mileage, then the other will follow soon after as they are both wearing at the same rate.
For the same reasoning, I always change light bulbs in pairs.

The pumps did not appear original but indeed failed within days of each other..much noisier than the replacement and seemed to have end play from the feel of tipping end for end..I suppose I got the last fraction of life out of the brushes by remove/replacing and then they both failed..Now my electric engine cooling fans just had one in stop mode..I could tap it and it ran again and then stopped..then rapped it with a tool and now its good again for now..likely stuck brushes worn to their limit..

My car is at 200K with lots of new parts..some used replacement parts too..so I cant answer about the miles on the pumps..

Thanks for the thoughts..