W116 280SE ECU / Fuel pump

Hello members!

W116 280SE -74.
Original cause:
Small vibration when accelerating.
Checked:
Injection nozzles. Ok.
Maps sensor. Ok (checked by Volker).
Smoke test. Ok.
After the previous steps, the engine started.

Next:
Distributor, completely removed on the table, but only the
trigger contacts were opened. Ok. (Norbert's tool).
After this, the engine will not start!?
The fuel pump does not make a sound 2 seconds before starting.

Next, from the disconnected connector of the Ecu:
Pin. 16 - 11. 12.7 V.
Pin 24 - 11. 12.7 V.
Pin 16 - 19. 51 ohms.
Power on, pin 16 - 19. 12.7 V.

Connected to ECU and power on before starting 16 - 11. 0 V.

Questions:
Is that 51 ohms the correct value?
Is the ECU damaged?
ECU nr: 0 280 001 015.

Best regards
Jukka

Hi Jukka,
it makes no sense to measure the resistance 16-19.
If you apply ground (-) to pin 19, the pump has to run.
If you install the measuring-adaptor you own you can activate the pump by pressing the 'pump'-switch.
When the ECU is installed it switches the 'ground'-signal.

Regards
Norbert

Hi Jukka and Norbert,

Jukka has already measured that there is ground on pin 19 by measuring against pin 16. So it is cables, fuel pump relay and fuel pump itself.

Hi Jukka,
I'm sure you search at the wrong place.
You removed the distributor without taking care to reinstall it in the correct position.

You have to correct this - only Mercedes shop-manual or another guide can help you. 
I'm no Mercedes-guy and can't help you.
Don't know where the information for the M110 is available.

Regards
Norbert

Hello Volker and Norbert!

Pin 19 and ground connected:
The fuel pump isn't running, but I can hear the relay clicking in the fuse box.
There are two relays there: the fuel pump relay and the main relay.
I just don't know which is which, since I don't have a wiring diagram...

One relay socket has 12V at pin 30,
and the other relay socket
has 12V at pins 30 and 86.
I'd like to know which relay is for the fuel pump so I can test the wire running from the socket to the pump.
There are no numbers on the relay sockets.

Norbert:
What do you mean by the distributor being installed incorrectly?
The flywheel and camshaft marks are aligned, and the distributor rotor is pointing to cylinder 1.
Is there something else wrong that I've missed?

Ps. I haven't tested the test adapter yet, so I didn't dare plug it into the socket).

Best Regards,
Jukka
 

Hi Jukka,
the pump relay is a slave of the  main relay.
When you remove one of them and it still clicks when you turn ignition on this is the main relay.
I think the distributor isn't set to the ignition-but to the opposite position - the crankshaft makes two turns while the distributor makes one.

Regards
Norbert

 

Hi,

what really puzzles me is that there is no reason why fuel pump should not work after distributor removal and reinstallation.

There is one more possible problem: Did you leave ignition 15 ON for long time? But that would also not harm ECU only igntion module, power resistors and ignition coil.

Hi Jukka,

Yes, I agree with Volker and Norbert. There is no logical reason why your non-start issue should suddenly have something to do with components that you haven't even touched and as such have nothing to do with the distributor. I think you need to work backwards from where you originated and check a few other things (#5-6):

1. Pull the distributor and re-check that the trigger points are undamaged and set correctly
2. Make sure that the plug for the trigger points is firmly seated
3. Make sure that the green coil wire is firmly attached to the distributor housing 
4. Make sure that the distributor is mounted correctly (and of course that the rotor arm is in place) - ask me how I know 
   
5. Did you disconnect the battery during the process and can it be that the feed to the ECU from the positive battery clamp has lost its connection?
6. Is the plug to the ECU properly seated after you have had it disconnected?

Best, Peter

Hi everyone!
I agree with Volker that the ignition circuit is not related to the fuel system.
Volker, Norbert and Stefan:
Thanks for the tips!
I’ve checked the distributor several times. I haven’t disconnected the battery. The ECU connector is fine.

I checked the ignition coil and ballast resistors anyway.
Ignition coil:
0.5 ohms and 4.36 kohms.
Blue ballast resistor: 3.1 ohms!? (should be 0.4 ohms).
The other ballast resistor: 0.7 ohms.
In the dark hours of the early morning, the fuel pump crossed my mind.
So, I disconnected the wires from the pump.
Ground: OK.
Connection to fuel pump relay pin 87: OK.
Power directly from the battery to the pump: the pump works.
Wires reconnected, relays back in place, and I tried to start it.
The pump runs for 2 seconds before starting, just as it should!!! What!!! 
Was the pump stuck...
The engine starts but immediately cuts out. 
What is causing this?

BR
Jukka

 

Good progress, Jukka. A bad ballast resistor can cause the engine to stall immediately after starting. The blue resistor seems to be resisting too much!? Seems odd. Please check in that area. Something is not right.

best, Peter

Hi Jukka,

While crankung engine 0.6 Ohm resistor is bypassed and only 0.4 Ohm is used. After cranking broken power reistor will block voltage to coil.

...exactly the other way round is right, the 0,4 Ohm resistor is bypassed while cranking !