86 560sel Mercedes-Benz

Wouldn't you think there is a good reason that there are 2 pumps on this vehicle? I would think it would not work well. Perhaps replace or repair the defective pump?

Ok you told me something i already know but you can use 1 pump to get by temporarily and you cannot repair a fuel pump that separates from itself the cap that sits inside the barrel of the pump cameout it was a defective part i will not order another pump online again.

If the pump is an inline pump you could bypass it by removing the pump and plumbing in sufficient fuel line to go around it, but the line would need to be of sufficient type to contain the pressure of the other pump. If it is in the fuel tank I am not sure how you would do that. Pretty sure you are familiar with all this. The other option would be join a vehicle specific forum and ask the question you asked here. Best of luck with it sir!

Bypassing one of the pumps would not be a good idea. You are best replacing both at the same time, if one has failed. The purpose of the second pump is to boost the fuel pressure from the feed pressure created by one pump to the operating pressure required by the CIS injection system.