Saffs,

I'm planning to rebuild my carbs over the summer - they seem fine, but they're an unknown quantity because the car sat for 8 years before I got it. Any recommendations on a reference for rebuilding and tuning them?

Emanuel

Help needed Mercedes 280E CIS
 

I am helping a friend try to get his Merc 280E running. UK spec.

It’s been stood a couple of years and now won’t start. With some gas it starts and runs while spraying so the problem appears to be in the CIS system.
I am a retired mechanic but have never seen this system before. I have tried to research and have made Adaptors to test the pressures.
It has a new fuel pump and filter.

Pressure direct from the pump at the CIS head is 5.8 Bar = 85 Psi ok I think ?

Pressure to the injectors is 2.1 Bar = 31 Psi. low I think ?

Correct me if wrong but the head pressure is low?

I need to make more Adaptors to make more tests but was going to check the pressure from the flow valve built into the head? I did wonder if I block this at least I can run it if the pressure rises and be sure everything else is ok?

Can someone point me in the right direction please as there seems little help in the uk

Thank you

The thread you are joining ended 22 years ago in 2002. Plenty of help here for CIS but I have two suggestions. This thread is primarily for the Porsche crowd. You will probably get more help on a vintage Mercedes forum.

Secondly, if you decide to stay here use the search function first as there is a huge amount of info contained in it. Then start a new thread.

Good luck

This is a good source of info, good luck.
https://cis911primer.com/home.html

Cis 101………….
 

Kerabo,

Two (2) critical CIS components you need to get familiarized with:

• WUR (warm-up regulator)
• FD (fuel distributor)

With the WUR, there are the CCP (cold control pressure) and WCP (warm control pressure) and for the FD, there are the SP (system pressure) and RP (residual pressure).

Lastly, you need to identify your WUR and FD. And make sure they are working and in spec. To get to this point, you must be able to test run the fuel pump manually with a fuel pressure gauge hooked to the system. Start a new thread for your inquiry. There are plenty of help available in this community. Good luck.

Tony

Mercedes is similar, but runs a slightly higher pressure.
http://forums.pelicanparts.com/uploa...1733261034.jpg

CIS is a robust system but everything needs to be in tip top shape. Before you tinker with the CIS components be sure everything thing else in the car is 100%. Plugs, points, dwell, timing, valve adjust need to be within spec.

To properly diagnose CIS problems, a CIS pressure tester is essential. You will also need to know the pressure specs for the car.

As the car runs when you spray fuel into the intake, you may have a gummed up fuel distributor and/or injectors.

If you remove the fuel line from the injector(s) does fuel flow when you lift the air plate and the fuel pump is running? If not you may have a gummed up fuel distributor.

If you pull the injectors and run the fuel pump, do they spray when you gently lift the air plate? If not you will need clean/replace the injectors.

This is why I chose Motronic. Adjusts itself.

If as Tony suggests either of those two items are out of spec get in touch with KMI (https://www.kmipetrolinjection.co.uk/)here in the UK, one of the best places for getting them reworked. My car ran like new after having them both done over a three year period.

Good entry point to get familiar with CIS:
https://files.bmwclassic.nl/E21/K-Jet/Bosch_K-Jetronic_web.pdf

A good basic understanding of how CIS works is mandatory and key to solve issues on it.

There are some good videos on Youtube teaching about CIS, I suppose this is also a good source for you as a retired mechanic.

E.g. Channel "mercedessource", playlists with plenty of videos:
https://www.youtube.com/watch?v=rW778EKLF9E&list=PLtRKk64pu2wp1txgW4sOqs7E rB2ilIRmt

He also has a website providing tons of information and tools:
https://mercedessource.com/store/1976-1993-cis-fuel-injection-trouble-shooting-guide

You mandatory need a pressure tester for CIS:
E.g. https://www.youtube.com/watch?v=87Uzf2_VUNA

Correct fuel pressures and air and fuel tightness are key on a CIS without absolutely no exceptions!

Thomas