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

nordfisch schrieb: Hi Sylvain,
the behavior is o.k.
Pressure is allowed to sink to 1,8 Bar - and has to hold then for a minute or so.

Please check your measuring device. We found out the manometers are misadjusted quite often.
Cross-check it with a reliable unit - maybe a tyre-manometer professionally used at a gas station.

Regards
Norbert

I did 7 tests with 4 different type pressure Gages.
I have noticed difference between - 0.1 bar, - 0.18 bars and - 0.3 bars.
All differences are constant with the tested gage.

I can confirm that my gage tool is probably a little lower than the real pressure, around -0.1 bar.

My previous results are mainly corrects.

Today i conducted a spray test of the injectors.

It take a little bit of time because you need to lift up the fuel rail with the injectors, remove the 8 bolts locking the injectors, the 2 bolts for the cold start injector and the 2 bolts holding the fuel regulator.
There was some cooper grease around the injectors, probably to ensure there is no leak at the seals. the seals were in good shape.



Here is my test bench with 9 water bootles.



The test is in the following video.


All injectors seems to be spraying correctly the fuel.
There is no drop of fuel nor leaking.

At the end the fuel quantity is more or less the same in all bootle.

I have tested with both of my ECU and the results are the same.

I asume my spray test shows that my injectors are OK.

I didn't get any fuel from the cold start injector. But i did make the engine run for 30 seconds before the test and it is a warm day today in Paris.

Hi Sylvain,

spray test is very rudimentary. Especially if you use large bottles as you did. Meaning you can hardly measure and compare volumes like that. You should have more equal shaped glasses. When I first bought some graduated measuring cylinders and tested with those I was surprised to notice a slightly more than 10% difference in injector volumes. After cleaning them they came down to 2-3%. With your bottles you would hardly notice 20% difference. Even with small jam glasses it is already difficult.

So all I want to say: Do not overvalue the spray test on volumes. It is good for checking leaks and spray qualitiy.

Hi volker

Thank you for your advice.
I will weight the fuel using a kitchen scale. It should be precise enough to compare the fuel quantity.

Also previously you told me "You also did not check potting". What is that ?

Regards
Sylvain

I have weighted the fuel quantity following my spray test.

Injector 1 : 6 g of fuel
Injector 2 : 6 g of fuel
Injector 3 : 6 g of fuel
Injector 4 : 5 g of fuel
Injector 5 : 6 g of fuel
Injector 6 : 6 g of fuel
Injector 7 : 6 g of fuel
Injector 8 : 6 g of fuel




For me it is ok.

i just need to open the kitchen window before my wife come home and get rid of the fuel smell.

Hi Sylvain,

having to empty the kitchen before house dragon returns home reminds me of something

I have done such tests and ultrasonic cleaning with graduated measuring cylinders on the balcony and got a lot of complaints due to the smell from balcony to living room. I should ask you the tolerance of your kitchen scale and I guess it is more than 1 g. I can really tell you that I was myself surprised when I did such cleaning and measuring with graduated glasses and found a more than 10% deviation on seemingly well working injectors. And their variation of far more than 15% really went down to less than 4%. Since then I am not so fond of my early spray test method versus marmalade glasses any more. It works to see leaking or badly spraying injectors. But the proof comes with varying speed and graduated glasses. If you have reason to believe they are not working properly, find someone with an ASNU service.

After several weeks, i am back.

Following my last test, the only remaining part that needed to be tested was the ECU. ANd finally I got it repaired.

The french post office almost lost the package but i magage to get it early july.

My ECU was missing some isolation plate and some bolt and washers.
With luck i had another (non working ECU) and took the parts from it.



I plug back the ECU to the car and ... it started the M116 right away.
The engine was working correctly even if i was on a basic ignition timing adjustment.

Cold start was OK
Cold idle was OK (around 1000 rpm)
Hot start was OK
Hot idle was OK (around 750 rpm)

After few kilometers around the block mainly to get some fuel, i descided to go to Le Mans Classic with the car.




A 3 days roadtrip (with some other w107) with outside temperature around 35°c.



Incredible week end, i even had the luck to get a full access badge to be very close of any part of the race track.


The car worked well in the hard conditions (hot days, lot of traffic james around le mans ...).
The average speed was 160 km/h on the highway, evenif the engine was a bit lazy around 5000 rpm.



I came back to Paris after 500 km of Djet testing and it was OK.
Great news after all the tests conducted on the car.

Two days afer my return to Paris, i took the SLC for a quick drive, only to have a breakdown 4 km away.

It was not caused by the Djet but only by the clutch system.
The clutch pedal was not coming up.


It came back on a recovery truck.


I ordered right away a clutch master cylinder, a slave cylinder and the small hydraulique pipe between them.

Then the fun started ....

It is a real pain to change the master cylinder due to the limited acces upside down.
It is killing your back too. I thought it will be the more complicated task and i was really wrong.

Removing the 40 years old pipe on the clutch cylinder was way more challenging.
I had to buy a pipe wrench (normal) and modify it (cut it in half) due to the very very very limited acces at the right of the gearbox.

Finally it was the hydraulic flush time. It took me even more time than the two previous task.

I tried a basic power (using air pressureas i do for the brakes) bleed from the brake fluid reservoir (it is the same between clutch and brake), only to find a very soft pedal.

I tried a normal bleeding process with two mecanics, one on the pedal, one on hte slave cylinder bleeder. It was worse.

I tried to do a reverse bleed with a syringe, not working.

It was very confusing.

After some internet searching i found out that the clutch bleed is recommended to be conducted from below using the brake system.

You should pipe the front right bleeder to the clutch slave cylinder bleeder with a quite long clear soft pipe. I bought mine in a fish shop.

Then you proceed with a brake bleed in order to push back the brake fluid from the front right brake to the slave cylinder up to the master cylinder then the the cluth (but also brake fluid) reservoir.

After several days of work it was working again.

I then took well earned holidays.

Today i came back at the SLC.

It started right away after several weeks.


I know i have a small exhaust leak (new gasket are in the glovebox) and i i also remove the center box and change it to custom straight pipes.






I made some adjustment on the ignition timing.
And made a idle adjustment using the air screw.



Now i have regain all the engine revs.


I will finish my testing soon to verify if the timing adjusment had an effect on the cold start or on the general engine behaviour.

Hi Sylvain,

that is good news ! Good that you have finally fixed all your troubles. When it comes to ignition: Start wtih dwell and then adjust igntion timing at 3000/min and finally verify at idle and 1500/min according to workhsop manual. Last check vaccum adjustment.

And by the way:

I have another website only for MB 107: sternzeit-107.de with 300 technical articles (mostly in German) and even an English section.

I have a 0 231 402 008 distributor (TFUD8).



As asked here jetronic.org/en/forum/ignition/997-do-yo...31402008-distributor

It is the same as the 0 231 402 001.

So you should set the following timing : 34° @ 3000 rpm without vacuum

And verify the good behaviour of the distributor with the following measurment :
+-2° @ idle (750 rpm) with vacuum
between 16° and 20° @ 1500 rpm with vacuum
34° à 3000 rpm with vacuum




I do not have the contact points anymore.
It was changed for an electronic system.
So i assume the dwell adjusment is now irrelevent.



I have made several timing adjusment yesterday and they are not verifying the factory values.
I'll get a summary of my test soon.

I have just check my dwell angle.

It shows 22.1°. Instead of 30-34°.

When I purchase the car the ignition was not wired correctly.
The engine was working but the rev counter not.
The transistorized module was bypassed.



Some resistor where not plugged.



I have modified the wiring according to this diagram for electronic contact.





Now the rev counter is working fine.