350 SLC 1972 troubleshooting

Hello,

Last year I bought an Mercedes 350 SLC to make an historic racing car.
The car was not running very well but it was starting quite ok cold or hot.
Clearly not all 8 cylinders were working.
It has a manual 4 speed gearbox and minimum rust on the body (I've seen most of the manual car available in Europe at this time, and some were really rusted).


I did a cylinder compression test, all 8 were ok.
I did a plug spark check on all 8 cylinders, i was ok.

Clearly there was a problem with the injection system.

I bought the car in Netherlands and bring it back to Paris on a trailer.
The car was sold new in Germany in 72 and came in the Netherlands in 99.

At first i took care of the rust.
Then stripping the interior, adding a rollcage, installing race shock and springs, racing brake hoses, race seats, rally radio and some other FIA compliant items.

With the car came some spare parts and another ECU in the trunk.
The car was starting fine either cold or hot.
The idle was rough but stable.
It seems to be working better at higher revs.

I did try the other ECU and the car was running very badly with some black smoke.
I put back the original ECU back in the car.

Two weeks ago after adding a voltmeter on the dashboard i try to start again the car And the idle was not stable anymore and the car not reving.

I really needed to get deep into the website and start to troubleshoot the engine.

First I tried again the spare ECU, the car was running as badly as before with it but at least it stared.

Then I tested the 25 pin ECU connector with my multimeter.



The air sensor was ok,
Injector group value were high on group 1 and 4 around 3 ohms
Map sensor values were ok
Throttle switch is ok
Ground and power supply are OK
Fuel relai is OK
Trigger contact are of limits
Water sensor is OK

I have check the injectors to see which one were not working.

With the car history, I had an invoice for the injector cleaning few years ago.
So I started with the wires, they were OK.
The injector resistance is OK around 1.2 ohm with a direct test.

The problem was from the plugs.
I renew the connections and now it is fine.

I then try to find a way to test the trigger contacts.

I added some wires on the TC connector on the distributor ( which by the way is 0231402008 ant not 009) in order to check the dwell angle with my multimeter.



I then start the engine and did the following test.
TC4 then TC1 then TC2 then TC3



The contacts seems to be off wear limits and the TC3 really wrong with 344°.

I then remove the distributor to check the trigger contacts.

First I did a simple test to check the contacts with some masking tape and a 4 colors pen.









All seems ok not compliant with the dwell test above on TC3