K-Jet fuel pressure test part 1

I’ve been trying to get to the bottom of the running issues on my 1979 280SE.   The last thing I tried was draining all the fuel and replacing the fuel filter and tank strainer.    Once the car warmed up, it actually ran reasonably well.    I took it for a drive for about 40 kilometers and it was running better and better.    After this drive, I assumed that the running issues was due to bad fuel and that I had solved this part of the problem.

However, when I needed to start the car and move it out of the way it was back to the same stuttering and lack of power.   I figured that perhaps my issues were something to do with the cold start system.    The next step was to run a K-Jet fuel pressure test to isolate the problem.    I’ve run these tests on the KE-Jetronic system, but regular K-Jet is a little different.    I found three resources that helped me here.   This page,  which gave really easy to read instructions was a good starting point.   I also found the Mercedes-Benz Continuous Injection System (CIS) Diagnosis & Adjustment – (1976-1979) Manual very useful, as well as the M110 engine workshop manual.

To perform the K-Jet fuel pressure test the first step is to connect the gauge set.   The K-jet system doesn’t have the test port like KE-Jet.    From what I could see, the gauge set is plugged in between the fuel distributor and the warm up regulator.

K-Jet fuel pressure test
The outlet looked like it went into the top of the fuel distributor.    The other side went into the warm up regulator.   The instructions called for it to go into the larger fitting.  However, I had one metal fitting and another one looked like a flexible hose.    I kind of figured it was probably the metal fitting.   At this point I also had to disconnect the electrical connection.

K-Jet fuel pressure testOnce I bypassed the fuel pump relay, I was able to test the system with the help of a friend.   However, while the gauge started registering pressure, I was getting a steady stream of fuel from the disconnected metal line at the warm up regulator.    Tracing this back to where it came from, it looks like it is coming out of the return line from the warm up regulator.

I figured that I probably have the lines mixed up, but I find it odd that petrol would be coming out of the return line.    I wonder if this if this is normal or points to some fault with the fuel distributor? Before I go any further it is worth investigating why fuel would come out of this line.   I also need to check if I have the lines back to front.

Since I am not sure if the lines are connected properly, the results may be meaningless, but I registered 5.2 bar on the test gauges.

Update 22/2/22: Looks like I had the wrong port on the WUR.   I will need to change this and re-test.  

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