W109 3.5 engine restless, no stabile..turn off when teperature is normaly

Dear MB friends,
before 11 years I buy in Germany MB 300SEL, W109, 3.5, V8, 1972.
Body complete restored, on engine make big service before 6 years. I don't drive car, only every two-three weeks turn on in garage. I write you about some problems and please kindly for help.
Problem 1: Engine start cold or hot every time at first, but no work stabil. He is restless in cold and warm condition. Accept gas but not immediately.
Problem 2: When engine come at normaly work teperature, work litlle more and than turn off. After 3-5 minutes, engine normaly turn on, but after few min. one more time turn off....In this circle engine temperature every time is normaly.
Thank you very much and best regads, Mladen/Zagreb

Hi Mladen,

when a car has been standing still for so long several things typically happen:

1. Rust and dirt in tank block outflow -> check by looking inside
2. Fuel quality gets bad -> replace
3. Fuel filter blocks fuel flow -> Replace fuel filter
4. Fuel pump gets sticky and does not transport enough fuel afterwards -> Check flow rate and fuel pressure
5. Injectors stick -> Check vibration, spray and whether they close properly

That would be my 1st approach.

Dear Mr. Volker,

thank you for your quick answer..It's nice to know that have skilled people who are willing to help.
About your answer:
1. OK
2. OK
3. Fuel filter change before 6 years
4. Fuel pump change before 6 years (please information hove much must be pressure)
5. Injector stics clean at laser system, check and pressure are good

Also please your opinion about my second question why engine turn off when come on work temperature.
With respect,
Mladen

Hi Mladen,

well a 6 year old product can well get stuck in that long time, even it is was new.

I do not understand problem 2. Do you describe that warm engine suddenly stops, can be started immediately again and then stops again?

Dear Mr. Volker,

cold engine start at first, after 15-20min..stop. If you want turn on right after it is extinguished..not possible.
Must wait cca 3-4min. (when temp.go litlle down) and than engine turn on at first time.
In warm state, engine work cca.5min. and once stop.....must wait 3-4min. and turn on at first....Every 5min.stop and must wait when temp.go litlle down.

When I drive car on test polygon, in one time, engine also stop.

Thank you for your time and nice evening,
Mladen

Hi Mladen,

you need to check what is missing when engine stops:

1. Fuel pressure (2.0 - 2.1 Bar)
2. Injector pulses (Do they vibrate)
3. Strong spark

From the missing point we can start to go deeper.

Dear Mr. Volker,

thank you for your opinion. When check all, I will inform you about situation

Nice evening,
Mladen

Dear MB friends, dear Mr. Volker,

after checking all the gasoline-fueled elements (gas change, visual control of the tank cleaner, gasoline filter, petrol pump pressure, gas flow through pipes, pressure in the nozzles, spark plugs ...) we discovered that the gasoline relay wich located below the computer, not working properly. After when engine running approx. 15 min. relay is overheated, close the fuel supply and the engine stops. After a few minutes, when inside relay temp. go litlle down, works again..in cyrcle. Relay is changed, and engine now runs as long as it has gasoline
Thank you very much for support and best regads,
Mladen

Hi Maden,

thanks for the feedback. A rare fault that you discovered.

Hi Mladen,
I had the same problem before - described in this thread, with photos: jetronic.org/de/forum/jetronic/42-proble...-dem-hauptrelais#187
(relais is a slightly different Bosch-type, not a Mercedes-car...)

The problem occured after more than one hour's drive - quite difficult to find.

Congratulations!

Norbert