Engine starts then stops. I'm at my wits end!!!!!!Help

[31348]

have a 1975 350 SL running on a Constant Injection System (CIS) fuel system, not K-tronic.
I have a engine running problem, my best way to describe it would be:-
If I can get the engine running ( from cold) it may run on 8 cyl. for 1-2 mins then onto 4 cyl then cuts out, or goes from 8 to off. If it restarts, it may be on 8, 4 or not start.
We have had the control unit (situated in the N/S/F wing) checked and is ok, (unless there has been a new problem occurred since it been checked) .
New pick up sensor located at the bottom of the dizzy.
Checked fuel relays, not got new ones but cleaned them and they seem to be working ok.
New HT leads etc.
Had a look at throttle body air flow sensor, seems to be working ok, but how can i carry out a test on it? eg 4 wires plug, when should they be onn or off?
Earthing wire cluster for injectors checked, seem ok.
Questions:
Does it matter which way the injector connectors are connected, eg there are 2 dimples on one side of the connector, should the dimples face up or down?
Have you any ideas what or where the problem is?
We have had the car for 2 years and are at our wits end to solve this problem.
Any advise would be most appreciated.

 

[Andy]

Hi

If I have read your post correctly, the vehicle is fitted with electronic injection. Cold start problems I would remove the base contacts which control the injectors in the base of the distributor. Follow the main electrical lead on the dizzy. You will have to remove the distributor to gain acess. Inside you will find a number of sets of small points. If they are covered in oil. Clean with petrol & blow out debris. Also make sure the ballast resistors are not cracked and causing a problem. Usually sited on the flitch close to the coil.


Good luck

Regards

Andy @ www.mercedesservicing.com

 

[leith]

Seems to me that the fuel pump works when the starter is operated. That's normal. But does not do so when the starter is not operating.

An oil pressure switch or a manifold vacuum switch will operate the pump through a relay, after starting. If the switching does not work (a very common problem on many makes) the engine will misfire after a minute and soon stop.

I suggest wiring so you can hear the pump when the ignition is on. If the car then runs OK, track down the switching source and correct it, though maybe the fuel pump relay is the prob.

(If you know the FP relay and know the pump contacts, then remove the relay and jumper so the pump is on with the ignition on and the relay removed)



The switching source is (only!) a safety device in event of an accident to stop fuel spillage as soon as the engine is switched off.