HELP!! 280 SEL starting and idling problem (after automatic choke cuts out)

[Andrew280SEL]

Hey there everyone. I now own a 1979 280 SEL with CIS Mechanical injection.
The problem I'm having is it's extremely hard to start and even when it does get going it will only idle while the automatic choke is on and after that cuts out it will die. It always had a slight miss (since I recently bought it) and lack of mid range power, but then it got worse having to go from Drive to Neutral to keep it going at traffic lights, and is now pretty much un-drivable.

As I said it takes a lot of effort to get started (it kicks constantly but never quite fires unless you really pump the throttle) and will only idle, (and well I might add) with the automatic choke and when that cuts out it wont idle unless there is throttle.

My dad has three (w116's) and has had two of them for years, and now a third one, and has never had a problem like this! The only difference being mine of course has CIS injection while his has electronic.
Any help will be greatly appreciated!

[Denis]

Hi andrew280sel

When you buy one of these golden oldies, the first thing to do is replace fluids and filters.

For the K-jet that means a new fuel filter. If it is clogged, the car will do as yours does. It may not be the answer to your problem but is the first step. FYI there is no automatic choke on this system but a cold start valve and fast idle device.

K-jet can be very reliable but you may need to sort out your "new" car 

Denis

Paris, France

[Nutz]

Test the fuel pressure,volume and spray pattern of the injectors.

[Andrew280SEL]

Thanks very much for that prompt reply guys and info. I'll take it on board and let you know the outcome.

[Andrew280SEL]

Hey there! Just letting you know our progress on the old girl.
We ran a fuel delivery test and got 750 ml (They say it should be a litre) in 30 seconds. Sure it's a bit less than a litre but every mechanic and (so-called) experts said it's plenty to get the car up and running!

Anyway, we took your advice on the filter, Denis, and got a new one which will help the delivery amount but as I said the previous amount was certainly enough. Anyhow we have came down to spark now we know fuel is no problem. We tested spark on one of the leads and it was the smallest little spark you could imagine. Nothing like the power the ignition system on these things should be putting out!

We hooked up a test light to the coil... absolutely nothing, even when we cranked her over. Whereas Dad put the test light on the coil in his 450 SEL and the light came on strong with the ignition in the "On" position.

Thanks for pointing us in the right direction, we have come down to the electrical system  and if all goes well she will be running in know time!

I'll let you know when it goes, and if you know anything else we may have overlooked please tell. Thanks again.

P.S I forgot to mentio we poured fuel straight down the intake and even sprayed Aerostart down there as well. Still no peep....

[Bandolero]

Could be your ignition module. Grab a secondhand one from the wreckers and see what happens when you connect the leads onto it before unbolting the old one off the car. Hopefully that is the problem.
I have found the mechanical fuel injection cars like the 280E, 280SE and the 450SEL all have the same part number, so they should all fit your car.