1989, 15,000kms 420 SEL Engine Problem

[SEC80Y]

Hi guys,

New to the forum but not completely new to Mercedes. I recently purchased a LHD 1989 W126 420 SEL with the super low mileage of 15,000kms. I have a massive history file to back up the mileage, also the condition of the vehicle strongly indicates that it is completely genuine, the black leather is like new, no rust at all and spare wheel/toolkit/first aid kit are all unused.

The car starts from cold completely fine but after a minute or so the engine dies. When you start it again for the 2nd, 3rd, 4th time the engine will cut out quicker and quicker until on the 6th or 7th attempt it won't start at all and then you have to let it sit for quite a while before it eventually repeats the same cycle.

Would anybody have any ideas as to what it could possibly be? Or perhaps direct me to a specialist in or around the M25 area who may be able to help?

Thank you

 

[taleff]

Hi,
I am an ex MB Australia tech, and when this model came here around 1986, it was one of the first with catalytic convertors. So the Bosch fuel injection was changed as it needed fuel mixture control (Bosch changed K Jetronic to KE Jetronic). There where several changes/enhancements to the system which I wont talk about. If you need more info look up Bosch KE Jetronic or CIS-E.
Part of this upgrade included fitting dual electric fuel pumps as fuel delivery need to be much higher. If one of the pumps has failed this may cause a problem like this. But with such low kms I would be surprised. Firstly I would drain all fuel out of tank, make sure there's no contamination in the tank, by removing the in tank strainer. Also the big filter must be replaced at this age. Fuel delivery is 1 litre within 40 seconds.The fuel system pressure with OEM gauge is 6.2-6.4 bar. The fuel pumps need to be tested independly. Sorry I no longer have the test procedure documents.
All other specs are from genuine Mercedes Benz Tech Data Book for engine 116 (420).
All the best taleff

 

[E55BOF]

Is it possible the fuel tank vent is blocked?

 

[ianrandom]

Sounds like quite a find. I'd want to check that tank/fuel/strainer/filter too.

Is Reading too far away for you? Star Motors is excellent with these cars.

 

[logman]

Fuel filter/fuel line restriction possible fuel pump failure soon

 

[SEC80Y]

Guys many thanks for the helpful answers so far

 

[SEC80Y]

Sounds like quite a find. I'd want to check that tank/fuel/strainer/filter too.

Is Reading too far away for you? Star Motors is excellent with these cars.

Star Motors are not too far from me, probably only 15 miles down the road. Must say I've only read positive reviews about them but have never used their services myself.

I want to use a specialist that not only knows what they're are doing but won't have my pants down either. I recently put an old Daimler into a local specialist and some of the charges that they came back on the invoice were laughable

 

[ianrandom]

Yeah I know what you mean. Star Motors is awesome, I've used them loads for my 420SE and SEC and only have good things to say. Especially because of the knowledge of these older cars, they will often know whats wrong without even looking.

 

[SEC80Y]

Yeah I know what you mean. Star Motors is awesome, I've used them loads for my 420SE and SEC and only have good things to say. Especially because of the knowledge of these older cars, they will often know whats wrong without even looking.

I've got a friend who used to be a Merc tech at Greenoaks, he's coming over today to have a look today and if we have no luck then I'll give Star Motors a call.