Good, it would appear that the system is reasonably tight.

With respect to cold starting (<60F ambient), the cold start injector (CSI) usually provides enough fuel to effect an immediate start, although if the rest of the system is not supplying fuel the engine will probably stall in a couple of seconds. If this not the case, both the electrical components and the fuel supply to the CSI will need to be checked. The electrical supply to the CSI probably passes thru a "Thermo-time" switch, and maybe a relay also.

If the key switch is cycled 3-4 times to build up fuel pressure without cranking the engine, is the starting performance thereafter changed?

when cycling key 3-4 times to build up pressure before actually cranking, the starting performance doesn’t improve.
Also with CSI connected, the car starts much worse : I need to push the gaspedal fully down during cranking of about 5 secs before engine catches
With CSI disconnected, the car starts better ( catch after 2 secs) but I still need to push the gaspedal fully down
If I don’t push the gas pedal fully down in both cases, you need to add an extra 2 seconds before engine catches
I measured the resistance of the thermotime switch and it was ok.
It seems as if I get too much fuel only during the start…

With this in mind, take progressive steps at leaning the main mixture setting. The screw in front of the fuel distributor may be moved in the lean direction (CCW) 1/8th of a turn at a time. If it is indeed the cause of starting richness, a point will be reached where there will be a lean no-start. Keep track of the moves!!

Frank,

I did lean out the mixture but then the engine
will run even worse at the point that it cuts down
And it doesn’t help the startup
But today I try to start my engine cold with CSI disconnected and gaspedal fully pressed down
And it worked like always. But please notice that it always generates a blue/ black smoke
And engine kept on running roughly even when warmed up. Heavy acceleration was bad
Then after a 1h drive, I let the car cool down for 5h
Ambient temperature dropped till 16degree Celsius
I decided to connect the CSI but before starting
I loosened the inlet and outlet fuel connections on my WUR
I waited about 20 min
Then I fastened both connections again
Now I tried to start: car started immediately
And I also did not hear any squealing sound when pump primes before the start

So I am now trying to see whether vacuum is holding my plunger up after cooling down the engine

I will do the same test tomorrow morning

I wanted to share some videos but currently it is not possible on this forum

Frank,

I did lean out the mixture but then the engine
will run even worse at the point that it cuts down
And it doesn’t help the startup
But today I try to start my engine cold with CSI disconnected and gaspedal fully pressed down
And it worked like always. But please notice that it always generates a blue/ black smoke
And engine kept on running roughly even when warmed up. Heavy acceleration was bad
Then after a 1h drive, I let the car cool down for 5h
Ambient temperature dropped till 16degree Celsius
I decided to connect the CSI but before starting
I loosened the inlet and outlet fuel connections on my WUR
I waited about 20 min
Then I fastened both connections again
Now I tried to start: car started immediately
And I also did not hear any squealing sound when pump primes before the start

So I am now trying to see whether vacuum is holding my plunger up after cooling down the engine

I will do the same test tomorrow morning

I wanted to share some videos but currently it is not possible on this forum

Here is a movie of the squealing sound
If I don’t have the squealing sound, the car starts perfectly :
https://youtube.com/shorts/4MBwClNAWqQ?si=sPQl-aFT28po2dA3

The squealing is the typical sound of the injection nozzles!

I believe that you are correct about the drawback of the metering plunger.
Bosch went thru two steps of corrections to try to remedy that problem; first was the addition of a spring above the plunger, and when the aluminum fuel distributors were introduced a relief valve was added to the control pressure circuit.
That relief function is what you did.

Any idea where I could get a spring for my plunger since my FD is cast iron
type 438 100 027 ?

I performed the relief action with cold engine and warm engine and engine started immediately without squealing sound

Cis Flowtech, 9389 Twin Beech Rd, Fairhope, AL 36532, US

CIS Flowtech did not really answered my question whether my FD needs such a spring...

Any idea what can cause such suction in the fuel lines, holding my plunger up ?
Between my WUR and top of FD there is also a diagphragm damper.


Could this be a possible root cause ?
I checked the damper and I can blow air easily through it, so it is not blocked.
Any idea what the small screw is used for on this damper ?

kr
Gerrit

Dampers are found in K-jet systems in higher priced cars; typically they are added to the systems to reduce pulsation noise. The adjustment screw is probably to tune the damper to the particular installation. The damper is probably not a cause of the problem.

A change that you can make as a test is to disable the push valve section of the fuel pressure regulator (FPR). There are two o-rings in the FPR; the smaller o-ring is on the push valve. Remove it. Without the push valve o-ring the control pressure circuit will be open to the return line when the engine is shut off.