CIS Problems - PeachParts Mercedes-Benz Forum

alabbasi · #1 02-01-2009, 05:20 AM

Gang

I started working on another CIS car that I recently purchased, it's an 81 Mercedes Benz 500SLC. Once again it had the odd additional injector set up between the warm up regulator and the fuel distributor which I got rid off and replaced with lines.

The fuel pump was dead and the injectors were cruddy so I replaced the pump and filter, then removed and cleaned the injectors and replaced the seals and the white cups.

The car would still not start with the engine appearing to flood. I tried to back the richness mixture out as much as I could but the injectors continue to sing.

Furthermore, it seems like the fuel distributor piston is all the way up as the flap on the intake sinks quite.

I did remove the fuel line that goes to the top of the fuel distributor and used my blow gun to drop the piston. This worked, but as soon as we tried to run the car, it got jammed back up there,

Furthermore, it seems that I am not able to adjust the richness mixture anymore. The screw appears to now just turn freely.

Any thoughts as to whats going on here?

250 Coupe · #2 02-01-2009, 09:20 AM

See page two of this PDF.

You can see that fuel pressure and a spring should push the control piston down to keep it in contact with the air plate lever.

I'd say that the control piston is binding in it's bore due to corrosion. I've heard of folks cleaning it with maybe steel wool or scotchbrite but I'd be real careful.

I think you may have backed out the mixture screw until it came out of the threads. I'd guess that it will have to come apart to get it restarted.

Michael

loepke72 · #3 02-01-2009, 09:24 AM

I had a similar situation with my 450SEL when I got it up and running. I was messing around with the fuel distributor, had it apart for cleaning, and got one of the plunger cylinder O-rings damaged and leaking, causing full pressure fuel to flow into the area of the cylinder with the small slits. It was enough to hydrolock the engine, but with no damage except for some fuel in the engine oil. I suppose a sticking plunger could also cause this type of problem. Do you know what the pressures in your fuel system are?

alabbasi · #4 02-01-2009, 08:43 PM

So I have two cast iron fuel distributors, can I use either of those?

cth350 · #5 02-02-2009, 08:00 AM

Any fuel distributor with 8 ports on the top and the same number of ports on the side will do.

An early 380 or 500 is ideal.

-CTH

PanzerSD · #6 02-02-2009, 01:34 PM

Am I likely to find a CIS setup on my 78?

rs899 · #7 02-02-2009, 01:39 PM

most undoubtedly....

alabbasi · #8 02-02-2009, 03:22 PM

100%

PanzerSD · #9 02-02-2009, 07:35 PM

OK, good to know...CIS is more or less problematic than the EFI setups?

I'm trying to familiarize myself with the Gasoline systems. I got Diesel down pat..this 78, though a 116 is an enigma to me at the moment (but not for long)

250 Coupe · #10 02-02-2009, 09:56 PM

Quote:

Originally Posted by PanzerSD

OK, good to know...CIS is more or less problematic than the EFI setups?

I'm trying to familiarize myself with the Gasoline systems. I got Diesel down pat..this 78, though a 116 is an enigma to me at the moment (but not for long)

Once I got the vacuum leaks fixed, mine has been dead reliable. The fan clutch stranded us in downtown Seattle once but that's been it in nearly four years.

Have I directed you to the www.w116.org site yet? You'll find the service manual CD online there as well as a bunch of W116 oriented guys. You'll find me there as Papalangi (means white man in Tongan).

Search for threads on checking fuel pressure, that is about the only thing besides mixture and ignition timing that you will have to worry about.

You may have the Lambda valve and an O2 sensor, not sure what year they came online but that's the only electronics you'll find on a CIS system.

Michael

PanzerSD · #11 02-02-2009, 10:02 PM

I'm already in at W116 as Panzer450 of course

I was glad to see the service manual on the site, as I scuffed up my CD when I moved. Panic ensued, because I received the CD from an un-named Dentist in California.

I've been flipping thru the pages and pages of the forum absorbing anything to do with 4.5 engines...

250 Coupe · #12 02-03-2009, 01:45 AM

Here is the official source for the CD and a bunch of other goodies.

Just beware that if you order the wiring diagram, you might get one for a 450SEL, which is a completely different animal.