1984 R107 500SL - Plunger Setting in Fuel Distributor

Hello Sternzeit-107 forum members,
I am working on a 1984 R107 500SL that has been in storage for over ten years.

I changed the oil and performed a static cylinder compression test. Results showed all cylinders have adequate static compression.

I installed new fuel delivery and fuel injection components:
* fuel tank, tank strainer, outlet hose to pump
* fuel pump
* fuel filter
* fuel accumulator
* fuel injectors
* fuel return hose to tank, fuel vapor hoses

The fuel distributors' plunger was seized so in attempt to expedite the project I obtained a used fuel distributor reported by the seller to be tested good.

I completed the following tasks:

* thoroughly cleaned fuel supply and return tubes that are plumbed under the body

* thoroughly cleaned all tubes to injectors

* replaced tubes to and from WUR

* replaced intake manifold gaskets, plenum chamber to manifold seals, air distribution hoses, fuel injector seats and seals and all vacuum tubes and connections

* cleaned throttle body

* adjusted linkage

* cleaned and tested the WUR. I paid close attention to the filter in the WUR fitting.

* cleaned and verified function of IACV

* cleaned the filter fitting in the fuel distributor fuel inlet.

* installed new battery

* installed new fuel pump relay

Once distributor was installed I performed fuel pressure tests. Test data showed fuel distributor operating pressure and warm-up pressure to be within spec as per FSM.

I see no leaks externally and no leaks from distributor into airflow meter.

I installed new Bosch spark plugs. (I have since learned these can be problematic. I will be replacing with NGK non-resistor spark plugs.)

Now the engine will start instantly. It has strong stable idle when cold. WUR function performs correctly. After warm-up engine will idle at a stable 650 +/- 5- RPM for 1-3 minutes.

Then idle drops drastically, fuel smoke pumps out of exhaust and engine has no acceleration. Sometimes it stalls. It is very hard to start again warm.

I let the engine cool completely then repeat engine start when cold. I consistently see the same problem.

I suspected fuel distributor issues. I removed fuel distributor assembly to examine. It seems the main plunger has an excessive travel. I compered this setting to a known good fuel distributor from a running 500SL. There is visible difference where each distributors' plunger rests

I have read during a fuel distributor rebuild there is a main plunger setting to be measured and adjusted. But I find no specification for this measurement. Only that it should be measured before disassembly of fuel distributor and replaced in the same position after rebuild of distributor.

I have not rebuilt this replacement distributor. I have not changed its plunger position.

Am I headed in the right direction with this suspicion and is there a specification for plunger setting?

Thank you all for reading and for guidance and input.
Kind Regards,
Austin James

Hi Austin James,

another car and one that should not habe made it to the US as it was only for the rest of the world outside Americas.

The plunger position is anyhow changed into idle-position by mixture asjustment screw. So don't worry too much about that if you never disassembled your fuel distributor.

However you should have a catalytic system attached to your car. Something that was maybe not originally there and was installed when the car came to the US. Which system do you have? And can you remove it to run KA-Jetronic without it and see whether it will effect warm idle-run?

Dr-Djet,
Agreed. Even I don't deserve to be in the same room with this beautiful SL.

However I am in the only one in this intellectual desert even willing to work on these Mercedes.

Enough of my low quality humor.

There is no catalytic system present on this 500SL. It appears there once was an addition to the exhaust but it is no longer installed. There has been some hack job to remove whatever was once present.

So, like the 560SL, it falls on me to repeat the tests of fuel pressures, manifold vacuum and ignition quality and timing.

I will do this and report back with accurate data.

My concern with plunger position was solely based on supposition the fuel distributor may have been fooled with prior to receiving it as I have no access to its history. But I have no evidence to support this. It was, I need to say, spotlessly clean when it arrived, inclining my thinking towards a possible rebuild. But that answer is in the wind..

Is there however a specification of measurement I can refer to if for no other reason than to say I have measured this? Or am I adding useless fodder to my overactive imagination?

Thank you Dr D-Jet and other forum members .

Kind Regards,
Austin James

Hi Austin,

maybe your car over the years was adapted to a lot of leakage and wear in the system. It could be a good idea to try to adjust the air/fuel-rate. I've got the manual only in German, but maybe it helps you slightly. Turning the screw anti-clockwise leads to less fuel.

Best regards
Martin

Hi JA,

you will find what you are looking for in our English workshop 107er manual under Repair Isntructions - Engine combustion - 117.96x KA-Jetronic. You will find the 380 SL US there which already had a catalytic system and it is also described how to adjust such a fuel distributor in 07.3-105 .or 14-200.

There is a valve on fuel distributors with catalytic system that will either change lower chamber pressure (original on 380 SL) or control pressure. So I recommend that you check whether such a valce is installed near fuel distributor. It looks like a D-Jetronic valve. You need to identify what catalytic system was installed and whether it is removed completely or not.

Gullydeckel,
Thank you for directing me to this information.
-Austin james

Dr,
There is no frequency valve retrofit to this 500SL. The normal operation of the WUR regulator is the only influence of fuel pressure I detect

Also there is no pin 3 in the X11 connector to attach my scope.

The only emissions device I find on the engine is Exhaust Gas Recirculation

Aside from the removal of what may have been catalytic converter I see no signs of modification.

I have prepared a video of fuel pressures and vacuum readings I will attempt to upload here once I have edited to a length I can move from my phone to the website and still have essential information

viewable. IF you feel there is value in that.

Thank you,
Austin James

Hi JA,

in that case I propose that you do 2 things:

- Try to adjust idle-run CO as shown. In the links I have given you aou also find Martin's document in English
- Verify that you have correct injection components, especially ignition distributor, fuel distributor, air flow sensor, WUR. If you cannot find a list for EU cars, let me know.

Dr,

Very good Sir I will begin with verification of components.

What is the information you have containing EU cars' components?

The auto came to me with no known history other than being in storage for a decade.

In addition, the fuel distributor was purchased from an eBay seller with the description it fits euro engines of the M117 family.

Also, this thread contains info about the non-catalyst engine. I am reading to better understand what's going on

rc107sl.club/der-107er/zahlendaten/typen-aggregate-uebersicht/

I am reading this thread involving the removal of catalyst system

sternzeit-107.de/en/forum/forum-107/1555...sl-mit-oder-ohne-kat

I have read from the section in the manual you directed me to and I have performed this procedure. I have done this prior to starting this thread but it is good practice to perform this as I continue to

correspond with you in order to verify.

I do get a stable idle with good vacuum,stable ignition timing and acceptable acceleration. But several minutes into idling warm the engine begins to misfire intermittently and fuel smoke begins from the

tail pipe. The misfire is not constant and not so often it is disruptive of idle stability. But it is obvious. To me it behaves like a leaking injector that is dripping fuel, enriching a cylinder and possibly wetting a

spark plug. . But I have tested the new injectors prior to installation and again after noticing this issue.

This condition lead me to thinking the plunger may be out of place but reviewing the theory of operation and its interaction with the airflow meter arm this is not clear thinking.

Yesterday I confirmed the mixture base setting by first turning the set screw counter clockwise one and one half turns to ensure no fuel can be metered to injection ports then removing one injector tube

from the distributor, energizing the fuel pump then turning the set screw clockwise until I saw fuel just beginning to enter the open injector port.

Then I turned the mixture adjustment screw one half turn counter clockwise. I verified no fuel was entering the open port. I removed power to the pump, removed all injector tubes from the distributor,

energized the pump and noticed three ports of the right side (engine right, passenger side of auto) would begin injection before the remaining ports as I begin to slowly push in the airflow meter plate. At

this time I slowly and gently pushed the airflow meter to its full travel then looked inside the airflow meter to verify no fuel is leaking from the plunger down to the throttle. No external leak is present.

Perhaps these ports that are ahead of the 'start of delivery' (using a diesel injection term) are causing the corresponding cylinders to run rich? This could be resulting in intermittent misfire as the rich

injection to these cylinders loads the combustion and results in fuel smoke at the tail pipe?

Or am I again adding fantasy to theory of operation?

Hi JA,

for sure all 8 injectors should deliver the same amount at any given time. Normally this is measured by Bosch KDJE 7451. The idle-run CO should be adjusted with the screw you found and a exhaust gas tester. to 1.5% CO. Also check that HC is not too high.

Your failure can come from broken O-rings inside fuel distributor or from failing ignition. With the observation of unequal fuel dosing on your distributor I would recommend to do a fuel amount comparison test.

Thank you Dr-Djet,

I suspected an injection quantity comparison test is needed. I am preparing a test set now.

I will update the thread with results.

I appreciate you for consulting me

-James

Dr,

I failed to add this information and ask another question.

fuel distributor 0 438 100 111 12752 442

is of the design group with the tuning ports under the seal caps, one for each injection port.

So yesterday, after the tests/examinations I described in my previous post, I removed one sealing cap screw to access one tuning port of one of the three ports with 'advanced delivery' (?)

I made careful not of the original position of the tuner then with fuel pump power on I slowly carefully turned the tuning screw 1/16 turn counter clockwise then clockwise back to original position then

advanced clockwise 1/16 turn. After each adjustment I observed 'delivery rate'. This was only visual observation I did not measure quantity. But I noticed no visible change in delivery rate.

Unless you can say there would be a noticeable change in delivery rate I am just fooling around wasting time?

But these tuning ports are the way to calibrate the delivery rate to each injector?

Tanks again
-James

Hi James,

component list can be found at www.bosch-classic.com/en/internet/bosch_...e/fahrzeugsuche.html under Vehicle Search..

And no one should try to adjust a fuel distributor without a proper test stand. Find someone in the US who can check and possibly repair your fuel distributor. I never considered that anyone would try to ajust a fuel distributor. but I shoudl have known better with my experience on so many detuned 450 SL D-Jetronic MAP sensors in the US.