When we got our
UniMoG we also got some used spare parts to go with it. We chose
parts based on our VW experiences as to what typically needs replacing
on a 30-40 year old vehicle. This list included a spare water
pump, coil, distributor, wheel (2nd spare), and a spare fuel pump.
Having taken delivery of the MOG in the winter, we soon
discovered how difficult it was to start in a Canadian winter, or so
After much cold, cursing, and fuel, we discovered that the fuel pump
was not pumping enough fuel for a cold weather start. It also
turned out on an early spring trip that year that the spare was also
not able to keep up. We feel that the fuel pump issue explains
many of the complaints from many moggers. Our symptoms could be
tested like this:
If during this test you found that your maximum SUSTAINABLE speed is
at slightly less than full throttle, then this is due to a lack of
fuel being delivered to the engine (it's a very hungry 2.2L). My
theory is that the stock 404.1 fuel pump is just barely adequate for
supplying fuel to the engine. This theory checks out if the
Instruction manual is consulted. Some 404s were equipped with an
auxiliary fuel pump for continued heavy work loads.
- Find a very long slight grade or headwind into which you can
drive in sixth gear at full throttle. Part throttle won't do
- Note the maximum speed you attain.
- Keep going like this for a good five minutes or more. If
during that time your speed starts to slack off, then you may have
fuel delivery problems so proceed to the next step.
- Slightly ease off the throttle and see if you can get your
speed to pick up in the next few minutes.
Our solution was to put two 24V electric fuel pumps at the tanks and
remove the stock pump. This decision was made because the price
of a new Mercedes mechanical fuel pump and the new 24V pump were
similar and the 24V pump has a much higher output than the mechanical.
This did require the use of a fuel pressure regulator before the
carb. The MOG now starts fine in the cold.
Our installation is somewhat unique due to the fact that we have three
fuel tanks. To add to this complexity, we won't rely on just one
fuel pump to get us out of the wilderness (bad past experiences),
therefore we opted for two different brands of 24V fuel pumps.
Each one is described below with part numbers for reference.
This picture shows the fuel pump for our third fuel tank which sits in
the bed of the truck. The arrow points to the the Facet style
fuel pump with is rubber mounted to the frame rail of the bed just
above the stock fuel tanks. (P/N: 40164 - may be listed as
Purolator or others, ours came from http://www.jnelectric.com).
This is a common style of pump which contains very few moving parts,
but it is much noisier than others when running. In fact, when
it has no fuel in it, the pump vibration can be felt while seated in
the cab! It is important to note that this pump is BELOW the
tank which it pumps as electric pumps can push fuel well, but can't
Just below the fuel pump is an in line filter which is between the
tank and the pump. There is also an inline filter just before
the carburetor (a clogged jet can ruin your day). The large
number of hoses and tubes is due to the fact that we have three tanks.
Most 404s won't look this messy. We have also extended the
vent line from the stock tanks all the way to the back of the truck
because while running on the third tank, you get more venting and more
smell from the two main tanks.
This picture shows the fuel pump for the two stock fuel tanks. It is a
Stewart-Warner 24V diaphragm pump. (Ours came from Napa with a
part # of 82054). It is solid mounted to the fuel tank mount
below the center of the tank as per the manufacturers directions.
This is important as our first one quickly overheated and died
on it's first trip when mounted higher (again, electric fuel pumps
push, they can't pull fuel - hence the reason we have two pumps).
This pump has a built in filtration screen which is serviceable
by three screws. This pump also runs quieter than the other pump
once it has fuel. The two stock fuel tanks are T'd together such
that the pump draws from them both. This was done so that we
didn't need a third pump or to move the valve. Also, since we
have a total range of 1600 km, the two stock tanks provide a
reasonable reserve and there was no need to operate them as separate
Power to the pumps is provided through a switch on the dash.
This allows three options of 'top tank', 'off', and 'bottom
tank'. We also use a hand valve for selecting the tank.
This is located in the stock tank selector position. This
setup has been in place for over two years (20,000 km) and has given
us no trouble. Unfortunately, we now have a lot of rubber fuel
line, rather than the stock steel, which leaves us open to rodent
nibbling, among other things.