350 SLC 1972 troubleshooting

Yes, by the controlling person.

In those times, very any unit was controlled before leaving the production.

Regards
Norbert

To continue the troubleshooting , i focus on the MAP sensor.

When i did the resistor test it gave me correct values.
pin 7 to 15 : 93 ohms
pin 7 to 11 : open
pin 8 to 10 : 350 ohms
pin 8 to 11 : open

For more informations on the values it is here jetronic.org/en/d-jetronic/troubleshooting#Druckf%C3%BChler

The sensor seems unrepaired externaly with the original rivets.





I also test the vaccum hose from the intake manifold.
With the engine running it pulls some vaccum.

Then i use my vaccum pump to test the MAP Sensor.
It should goes from 0.50 bar (380 mmHg) to 0.45 bar (340 mmHg) in at least 10 seconds.

The measured time is around 10 seconds so i assume the map sensor is OK.



sorry it's upside down.

Following my Trigger Contacts problem (one of the lowwer arm was broken, i had inconsistant dwell angle value with one TC on the dynamic test), i received this week another part (thank you norbert).

There are some light differences.

- no broken arm
- no plastic covers around the contacts
- no felt used to grease the cams
- the ground wire is not welded at the same place




The triggers contacts are inserting much more firmly in the distributor and seems to find their place more easily.

I did a static test, with a multimer it all seems fine.

I did a dynamic test with the engine running.
It gave me the following results of duty cycle.
TC1 : 50% (180° Dwell)
TC2 : 51% (183.6° Dwell)
TC3 : 49% (176.4° Dwell)
TC4 : 52% (187.2° Dwell)


The dell angle is the angle where the contacts are closed.


For a ignition contacts there is several edge on the cam (one per cylinder).
For the injection there is only one edge per cam and two cams one above the other.
As the trigger contacts are made by pair on the opposite side, each cam will trigger one after the other the contacts.

To get from the duty cycle to the dwell angle you need to apply this formula.
dwell angle = duty cycle * 360 / number of edge.


It is a bit higher than the original values but there are all consistant.
I assume the trigger contacts are now fixed.

jetronic.org/en/d-jetronic/troubleshooting#Impulsausl%C3%B6ser

Did someone already did the dynamic test and get results between 135° and 165° or even higher with a working engine ?

Hi Sylvain,

as I had already told you via PM, I am currently on vacation. That's why I give only some short answers from Internet cafe. Please be patient for 1 more [strike]months[/strike] week. I appreciate how sytematically you check your car.

Just some short replies:

• ECUs were originally marked with colors on tuning resistors. No need to worry. What worries me more is that most people break off noses on the lid when removing it And I only know one source for new lids at 80€ plus VAT plus transport.
• Your MAP sensor seems on the brink of losing vacuum. Below 10 seonds is definitely broken. Normally it is more. I had a visitor on our workshop last year with 10 seconds. Now it is down to 4 seconds. You also did not check potting
• Other than ignition contact dwell on trigger contacts is not really important. Igntion contact's dwell charges ignition coil. But here only closing of contact is a trigger for ECU.

Please be patient for 1 more week, I promise to answer then.

Hi volker,

Do not worry i am not in a rush. Please enjoy your holidays.

I am just checking my car based on your work and sharing it with everyone reading the forum.

Hi Sylvain,
you are correct - the points unit you got from me is the older version.But this works fine, too - the fibre blocks need a little more maintaince, i.e. they should be regreased every 10.000 km for an almost unlimited life.
The distributor has a greasing-felt, too. It is located on the backside of the camshaft.

You could interchange the whole points unit from ane chassis to the other when having outsoldered the wires. Below rhere are two screws holting the very contact unit.
But I wouldn't do this.
The unit you got is in really good condition - and you can leave the other unit as a spare.
We noticed more then onte time workshops or users didn't install the points unit <still being sold by Mercedes / Bosch at a very high price> correctly and had trouble afterwards.

Regards
Norbert