CIS K-Jet Help needed
 

Hi All,

IF anyone can help me get the R107 back running I would be very appreciative.

I bought the car knowing that the previous owner said it needs a fuel distributor rebuilt. My buddy tried,,,

So fuel distributor leaked from one of the screws that holds it together. I disassembled and reassembled the fd (following CIS fuel distributer cleanout w/pics - Page 2 - Pelican Parts Technical BBS ) and the leak is gone, but the car still doesn't run.

When I crank, she fires right up, runs about 3-5 seconds and dies. So I know that the ignition is OK and that the Cold Start valve is spitting fuel for the start.

I tired half throttle, full throttle, no dif.

I am suspecting a block fuel return (when I took the fd apart most of the small O rings were torn, so there might be a chunk of rubber blocking the return. Problem is, I don't know which is the return. Also notice the messed up blue connector. I have no idea what that thing is for, or what it doe, but I don't want to keep messing with the fuel lines if the blue connector can cause a no run situation.

Any suggestions?

The car is a 1976 450SL with 86K miles.

m:

The blue connector is to a safety switch ("rollover" switch). With it unplugged, the fuel pump should run continuously. If the safety switch is defective, the fuel pump will run only when the starter motor is cranking.

Thank you Frank,

I know that it's a purely mechanical injection, so I couldn't figure out what it could possibly be for.

There are some other controls involved. This video is for VWs, but the operation is the same. Sure helped me get a handle on how the system works....

https://youtu.be/a4fJAfXYxWk

I recommend doing a proper rebuild of the fuel distributor. You can get the parts for it here: Fuel Metering Distributor repair kit for Bosch K - Jetronic 8 Cylinder - salvox

There's a guide on benzworld's r107 subforum on how to do it. Link: http://www.benzworld.org/forums/r-c107-sl-slc-class/2205337-cis-fuel-distributor-rebuild.html

The diaphragm that rests between the heads of the distributor can go bad. The act of separating it for the cleaning most likely destroyed it.

It's very easy to do and there isn't any need to keep the ceramic hats and springs together. You just need to make sure you keep it clean.

Try that first and report back. You may have to invest in a KJET fuel pressure kit to diagnose further.

m:

Just a word of caution:
The post above by "oyab" contains two links; both of them are for the aluminum FDs, not the earlier iron version which you have. Not only are the castings of different metals, the internal components are also quite different.

Thanks Frank.

The correct part is on this page.
Mercedes 450 SL Rebuild kit to repair Bosch Fuel Distributor 0438100012 - salvox

For the sake of records, I edited the last link to direct to their homepage. Penalties of posting on a mobile phone!

OH, I failed to mention that I have a 79 450SLC (rusted out parts car) that was running. So I pulled the FD and put it in the SL. Same thing, starts runs a few seconds and dies.

When I got the car the FD was leaking. I tore it apart and it was dry. Then it started leaking. So I'm wondering if the pressure is too high.

Plans are to pull the warm up regulator and pressure regulator from the SLC and install as a pair.

Frank, after some research, I think that blue connector on the mixture controller might be control the overrun solenoid, which energizes an air bypass around the sensor plate.

I noticed that the warm up regulator has a vacuum line going to it. That line was loose, didn't seem to change much when I tightened it.

Found this site VERY helpful,,,

https://www.slideshare.net/guestceff35/bosch-k-jetronic-fuel-injection-manual

It's not for a Benz, but I've found this site very helpful with my 911:

911 CIS Primer - Index

To the extent that any air bypass is present, it will be around the throttle plate (rather than the sensor plate), and would function as an anti-backfire valve. The electrical signal for that valve would come from a switch on the throttle shaft.

the blue connector is not for what you mention. it is the fuel pump switch. it has to be plugged in to run the fuel pump. good luck, chuck.

pf:

Quite correct, thank you; as stated in post #3.

I have the same problem with my 280SL (did not run for many years) and the problem was return fuel line to tank.
For testing disconnect return line and catch fuel to the bottle and engine should run.
God luck,

I think I found my problem!!!


First off, when I got the car she didn't run, and fuel leaked out from the FD where someone had tried to r&r the fuel distributor.

So I removed and tore apart the fuel distributor, bought some permatex tacky gasket sealer, thinned it with lacquer thinner and proceeded to paint to two halves before I put it back together.

IT didn't leak! but still no start. After many cranking attempts the fd started leaking. This led me to believe that the fuel pressure was high. I checked the return to the tank, and it passed air without much effort.

So, I decided to pull the pressure regulator and warm up regulator, and mixture control and swap out. THAT's when i noticed that the warm up regulator had a second vacuum port on the bottom. At which point I immediately realized that someone had swapped vacuum lines. The one labeled atmosphere was going to the intake, and the one labeled intake was going to the atmosphere (atmosphere being the 25mm air lines)

So, as soon as the car starts, vacuum is applied to the atmosphere port of the warmup regulator, and the diaphragm is pulled to the lower stop, thereby increasing fuel pressure.

So I went to swap vacuum lines, but they are different sizes and it "Looks" like it's supposed to be that way. So I'm going to swap the two vacuum lines going to the warmup reg from the SLC to the SL.

MAybe later today.