Mercedes 380SEC c126 engine problems

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Ediz1988

New Member
Joined
Dec 6, 2019
Messages
2
Location
London
Car
380 SEC c126
Hello guys, new to this forum. Basically my father passed away and left behind a Mercedes 380SEC 1984, just 68000 miles. There has been a issue where the car doesn’t want to start and when it eventually does power goes in D and cuts out then won’t start. I’ve had the RAC come and take it to a mechanic. Changed spark fuel pump etc and still the same. The mechanic is saying that there’s no spark when starting the car and could be a coil somehow, but would this cause this? A few people have suggested fuel pressure etc but the mechanic is struggling with the age of the car. All help with greatly appreciated thank you :)
 
Petrol engines need three things to run - Compression, fuel and a spark. Your car must have all of these in some amount otherwise it would not run at all. When you select drive on the gearbox it causes increased load on the engine. Your engine has a idle control valve which maintains the idle speed so it could be that there is fault with it or the logic circuit / wiring that control it. You mention that it stalls when you select drive. Does that mean it does not stall when you move through reverse on the gear change gate? Does is idle smoothly without any noises or smoking? Has the car been sitting idle for a long time? It may need a little re-commissioning such as plugs and HT leads but you do not want to be guessing at what it may need unless money is not an issue.
Your car is elderly but the technology is very similar to recent model cars and probably a little more straight forward to trouble shoot. Any competent mechanic should be able to help you. Ask them if your engine has L-Jetronic, K-Jetronic or KE-Jetronic. If they look at you blankly then go somewhere else.
1980's Mercedes are a thing of beauty and a technological tour de force of their day. Find someone who understands them to help you with it.
 
Has the car been sitting a while? If so the fuel lines could be gummed up with varnish that could cause the fuel distributor piston to stick or the fuel injectors to clog up. It's not a hard job but laborious and common to CIS engines.

There should be a million thread on the subject if you go to the Benzworld 126 or 107 forums.
 
We have had 4 w126 v8s and the fuel pump relay is very common
 
Petrol engines need three things to run - Compression, fuel and a spark.

Petrol engines need three things to run - Compression, FRESH fuel and a spark.
 
First thing I would do is to go to the fuse box and remove each cartridge fuse one by one and give each fuse end cap and the copper clips a clean up. You get galvanic corrosion due to the different metals used and the corrosion layer can give very poor electrical contact and irratic electrical behaviour. Plain plastic kitchen scouring pads are good for this as you don't want any metal material that conducts electricity
 
Just have the mechanic pour a little fuel into the intake and see if it fires. If it does, you don't have a spark issue. Next step is to remove the hose that goes into the fuel distributor and divert it to a bottle then crank the car. You should get about 1 liter of fuel in 30 seconds. If you're getting fuel to the fuel distributor, the pump and relay are fine.Now you can isolate to fuel distributor , lines and injectors. These are simple cars.
 
Agree with the comment about fresh fuel, as it's now blended with ethanol it goes off relatively quickly.

You can remove the fuel pump relay and bridge two of the pins to force the fuel pump on and eliminate the fpr.

How did the mechanic confirm that the spark is the issue? What was the condition of old spark plugs that were replaced?
 
Thank you everyone for your replies. I left the car with a mechanic for a week and two things they noticed and changed, first the rotor arm on the distributor which was gone and the ignition coil. Now the car starts fine which before wouldn’t. He suggested that the fuel pump relay on the vehicle was not for the 380 SEC engine and is a relay for the bigger models such as the 500 SEC and recommended changing that too. Is there any difference whether a fuel pump relay is for the 380 or a 500 for example would it could issues too? Thank you so much for the suggestions as you can see from the pic the rotor arm was badly gone lol so hopefully if the relay is changed too the car should be 99% back :)
 

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Sounds promising - That certainly is a nasty looking rotor arm.
I believe the relays are identical in the 380 and 500 models.
 

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