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Car Forum / Mercedes-Benz Cars / December 2004

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1972 W117 280SE 4.5 Fuel Injection Trouble

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dkhoshabo - 02 Dec 2004 14:39 GMT
Car been sitting around for 3 years. Finally got the engine to turn just to
find out the four middle electronic fuel injectors are either not getting
or, not providing the injectors with electricity. Figuered that out by
switching spark plug wires, fuel injector fuel leads, and fuel injector
electrical leads between the hitting and non hitting cylinders. I see the
electricity comes from the bottom of the distributor and cleaning the plug
has not helped. Any suggestions besides "Junk It!"? This is a daddy/son
project that I took up and its been fun. Obviousley, the sonny boy would
be very disappointed if his dream of going for a ride in the old junker is
squashed. In advance, I like to thank you for your advice.
Karl - 08 Dec 2004 14:34 GMT
Cleaning the connecter does not fix anything. That plug is for the trigger points.
You need to remove the trigger points and inspect them for oil on them. Unsnap the dist cap,
remove the rotor, remove the black cover on top, put back the rotor. Look around the top edge of the
dist for a notch. That is the #1 to fire index mark. Now get wrench and put it on the power steering
pulley nut. Turn it clockwise and hopefully the engine will rotate also. If not, then you will
need to hold the belts tight. If it still does not turn, remove the spark plugs. Rotate the engine
until the rotor points to the index mark. Now look at the crank pulley, the timing mark should be at
O.
Move it to O if it is close. Now you need a 5mm Allen socket with a 12" extension to go down the
left side of the dist to remove the bolt holding the dist in. Put grease in the head of the bolt so
you don't drop it!! Now lift up the dist. The rotor will turn to the left as the gear clears. No
problem, just remember that it has to be turned left when you put it back down so it lines up to the
index mark when it seats. Now lay the dist on the engine [green wire is still connected, if the tie
straps are still behind the power steering pump, cut them] and remove the 2 screws holding the
trigger points on. Pull the point assembly out. There are 4 sets of points. Usually they have little
clear plastic covers on them. Look carefully at each set. Open and close them and see if oil is on
the points. Look in the dist body and see if oil is in the bottom of the housing. If yes, your dist
is worn out and not repairable [I have tried to repair them for this problem by removing the shaft
and installing an O-ring to stop oil migration up the shaft but it does not fix it]. If the trigger
points are oil covered, replace them. Think about a new dist in the near future but not right away,
they are BIG $$$$.

If the points are perfectly good and there is NO oil in the dist, then you have one of 2 other
problems: either the harness has rodent damage especially where it goes thru the pass side firewall
or the ECU brain has 2 failed circuits.

Since there are 4 trigger points and 8 injectors...... the injectors fire in pairs. 1 + 5, 2 + 7, 3
+ 6, 4 + 8. Your cylinders are laid out like a Ford: pass side front to back is 1,2,3,4. Drivers
side is front to back 5,6,7,8   Your middle dead ones are 2 + 7 and 3 + 6 in pairs. The trigger
points send the signal back to the ECU to fire the injectors.

> Car been sitting around for 3 years. Finally got the engine to turn just to
> find out the four middle electronic fuel injectors are either not getting
[quoted text clipped - 6 lines]
> be very disappointed if his dream of going for a ride in the old junker is
> squashed. In advance, I like to thank you for your advice.
 
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