How do I change the fuel injectors in my 1983
300D? (240D, 300CD, 300TD wagon, 300SD, 300SDL)
Ok, first lets make sure it's the fuel injectors and
not just a clogged fuel filter. We'll also try to rule out timing, fuel
injection pump issues, valve adjustment and......
What is the car doing or not doing?
Does the engine run rough at idle, smoke, sound
like the injectors are nailing (loud clacking sound) when accelerating,
lack of power, shift hard or too early. Ok, these could be symptoms of
many different issues but we are leaning towards injectors.
Here is a rough test to isolate the issue. Get a
17mm wrench and start the car. Once the car is warm, loosen the fuel
injector line at the top of each injector one at a time. If the car gets
rougher when you loosen the line, that injector is still working, we
don't know how well but at least it is spraying some fuel into the
cylinder. If you loosen an injector and there is no change we know that
the injector is either clogged or squirting instead of spraying.
You can replace just the offending injector but if
one went bad the others are probably close behind.
We usually use Monark
(German) or Bosio (Italian) injectors, we figure the cost is close
to the Bosch replacement so we might as well get some added performance
for our investment and time. Install them in sets, don't mix with the
Bosch injectors, your car may still run rough but for a different
The Monark and Bosio injectors offer a more
accurate spray pattern with better atomization which translates to a
more complete fuel burn and more power. You will notice a Wider power
band, less smoke, smoother idle, quicker response, better fuel mileage,
the list goes on. Advance your timing and increase the fuel mixture and
you'll swear you have a whole new car.
Note: if you have a non-turbo engine these
injectors will give you a broader more useful power band which is really
needed in the non-turbo versions. This will let you move your shift
points a little later in the rpm range and really improve the overall
performance of you car. If you have a turbo version the improvements are
even more dramatic.