Why did some Mercedes come with 1 Fuel pump & some models two?
 

Ive been working thru fueling issues on two Mercedes ,both are the model 190e with the cosworth motor ,the 1985 model was fitted with just one pump ,while the 87 has duel pumps.I completed the 85 with a replacement tank installed followed by a list of new fuel related parts with good results on startup .I have know started working on the 87 , it seems to have the same issues such as the rusty tank but faired better than the 85 with a better maintinence shedule looking at some of the fuel related components.Since I want to give the 87 cossie motor a stir after its long sit of 10 yrs or more I was wondering if I could pull the fuel filter and pump setup off my 85 to make a run at it.A look at the wiring for the duel 87 fuel setup has double the wiring ,would it be alright just to wire both pos. and both neg. leads to the one leg on the one pump setup ?

chas:

If you will examine the plumbing at the dual pump installation, it's likely that you will find that the first pump out of the tank feeds into the second pump. Why are the pumps in series? To raise the fuel pressure above that which one pump can generate. [The volume is unchanged.] The higher pressure is required for the KE-Jetronic (CIS-E) system. The '87 has KE, the '85 does not. Hence, the '87 must retain a dual pump supply.

Ill come back with my findings once I have it started ,Ill try a fuel pressure reading at the engine and pull load to see if it drops.It might be fine to run it as it sits but may not keep up with daily driving.
As a side thought I began to research Mercedes fuel systems for the following years above these 80s models and found some interesting changes ,espiecially in the fuel pressure regulators. The 2000 500s for example has modified the fuel filter and FPR into one unit ,less parts to change out but makes since in that as a mechanic you would want to eliminate the chain of possible clogged parts for diagnoising as the service.

the reason for 2 pumps is volume. 1 pump does not do well, which is why mb went to 2. Ferrari and lambo with k and ke systems have 1 pump per bank of cylinders. good luck, chuck.

Here's a bit of mischief:
1) Der Schnuppester tells us:
"The 2.3-16 have got only KE-Jetronic from factory." Correct, 5.0bar 85-86, 6.3bar 87-on
2) porkface tells us:
" Ferrari and lambo with k and ke systems have 1 pump per bank of cylinders." Also correct, because each bank of cylinders has its own separate K or KE system. 5.0bar
3) I have said:
"Why are the pumps in series? To raise the fuel pressure above that which one pump can generate. [The volume is unchanged.] Also correct; when the pumps are in series the volume is determined by the first pump. [When the pumps are in parallel the volume is increased. see: porkface]

Interesting, three statements about KE pumps, all correct.

To the OP:
The '85 single pump is intended to supply a KE system that operates at a system pressure of 5.0bar. The '87 system operates at 6.3bar; the 5.0bar pump may, or may not, even supply enough pressure to start the engine.