560SL "Japan" poor running engine, PROBLEM SOLVED!

Hi Gunter,

well that is correct too. So we have 2 possibilities why lower chamber pressure is not 0.4 Bar below upper chamber pressure:

1. New EHA also fails - rather unprobable
2. Flow out of EHA through fuel distributor over pressure regulator to tank somewhere narrowed. That would fit your observation of air bubbles in reflow.

Can you disconnect the MT reflow line from pressure regulator and let it run in a glass? You have to close that open hole on fuel distributor then. But we would learn if pressure regulator influences this.

Hi Volker,

I think I understand what you are suggesting, but can you explain what you mean by "MT reflow line?"

Guten Abend,
Gunter

Hi Gunter,

sorry MT is short for Mengenteiler = Fuel Distributor.

Hi Volker
Thanks for the clarification. I should have known that.

While trying to find the partnumber on the pressure regulator, I could see that the ventilation tube has broken of, and was glued into place. So some-one has been tampering with the part before. I am going to have to replace it anyway (although the vent does not affect the function of the regulator), so might as well do it now, instead of trying to find a way to exclude it from the system, as you suggested, Volker.

I'm trying the logical approach here, assuming ideal conditions;

So the pump delivers 6.2 bar to the lower part of fuel-distributor.
The feedback line to the pressure regulator (the small tube between the feed-line and the return-line) allows the pressure in the lower part of the distributor to drop to 5.8 bar, but keeps the pressure at 6,2 bar in the upper chamber.
This pressure differential allows a metered flow of fuel from the lower chamber to the individual upper chambers, to the injection lines. Pressing the gas-pedal, adds fuel FLOW (not pressure), differential-pressure stays the same.

Am I correct this far?

After this, the ECU sends commands to the EHA to adapt the pressure differential, by allowing more or less flow through the EHA, following the input of various sensors to the ECU. This affects pressure-differential, allowing the ECU to enrich or lean out the mixture, up untill a fuel shut off, in effect, 0 bar pressure differential. (6.2 bar in both upper and lower half of the distributor). Air-flow stays the same, but amount of fuel flow changes, thus changing mixture.

The feedback from the fuel-distributor to the pressure regulator is constant, and unaffected by the ECU, thus allowing the system to work, even when all sensors stop working, and the EHA does not receive commands from the ECU, the so-called "limp-home" modus.

Am I still correct?

Now, is there a flow through the EAH when it does NOT receive a signal? Or is the pressure differential between upper and lower chamber achieved by the feedback line from the distributor to the regulator?
When measuring through the cold-start line (6.2 bar) and the check valve (5.8 bar), could I in effect block of the 2 small holes behind the EHA and still receive the same results?

Kind regards to all of you!

Hi Gunter,

fuel pump would deliver more than 6.2 Bar if it tube was blocked or less if there was not enough fuel from tank. Pressure regulator decreases that to 6.2 Bar. FD receives fuel to upper chamber from fuel hose directly in parallel to pressure regulator.

WHA without current will make 0,4 Bar pressure difference. It can vary via current from ECU from 0 to roughly 1 Bar pressure difference. And es it would be best to measure with a differential pressure gauge. A 0 diff. pressure means that there will be now flow to injectors. Your regulator is not broken when the small plastic leakage nozzle is broken off.

EHA lets fuel into lower chamber. Then there is an outflow from lower chamber through a throttle hole via that small hose to regulator and from there back to tank.

So now you understand why I try to find out whether your 0 Bar pressure difference comes form WHA, FD, hose or regulator.

I think I know what is wrong;
The main pressure valve in the pressure regulator is stuck in the “engine off” position.

It’s stuck in that position because of the massive and sudden pressure drop when I first removed the EHA valve.

Hi,

nothing is impossible - in a Toyota !

If it was stuck closed, your system pressure was > 10 Bar.

Volker,
Frohe Weihnachten!

Well, not stuck in the sense that is does not open (because then there would be no flow, and the car would not start) but stuck in the sense that it allows back-pressure to build in the distributor.
So yesterday I removed the pressure regulator to see if I could see something that was amiss. I pressed the valve with a piece of metal, from the return-line opening, and it does move.
I then poored some aceton into it, and worked the valve a bit.
I re-installed the valve, started the car, and then gently tapped the valve with a wrench-extansion and a hammer.

Before, the engine ran at 10%. I could start, but almost could not rev, I could not drive.
I took the SL out, and now it runs at 50%. I can drive up to 120km/h, but nor more.

I ordered a new valve, and will install it this week.

I think it is safe to say that indeed, the pressure regulator does not perform within specifications anymore.

Hi Gunter,
any progress? Just curious if my idea was right..
cheers, Werner

Hallo Werner,
happy new year!
well, today I installed the brand new pressure regulator, which was a 5 minute job.
But the problems are not resolved.
This is beginning te become a very costly exercise.
I installed a new pump-package, a new screen filter, a new EHA valve and now a new pressure regulator, with no improvement/solution for the problems.
I'm stuck now.....
The car ran ok, not perfect, but when removing the EHA valve to inspect the 2 green o-rings, all the problems started. I don't know if that inspection caused the problems....

I guess that I have to start all over again.....

Happy new year to you too, Gunter. 
Did you install all stock or oem parts? Hopefully nothing aftermarket.. Maybe one of the new parts is not working well too. If new parts would be always good there would be no warranty needed...
However, I would hook the car up to an emission tester, 
a tester showing CO, O2, CO2 and HC. 
If possible, take a picture of the screen at idle, and anotherone at 2000rpm. Please post these pics here. 
Did you check the oxygen sensor?
I battled a problem on my low miles 1980 500SL for almost more than a year, and finally I had a funny acting oxygen sensor which fooled my big time. Sometimes it can be very annoying.. 
cheers, Werner 

 

Hallo Werner,
The EHA and the pressure regulator are Bosch-parts with the correct part-number, bought at the Mercedes-dealer in my home-town. The pump-package are also original parts.
Maybe I can swap out the oxygen-sensor, but it looks brand-new. The former owner did good maintenance as well.
At the end of this month, the 560 will go to a specialised garage here in Belgium ( terrijnclassics.com/ ) who are going to go through the car to get everything sorted.

Hi, You can ask Martin...He installed 3 brandnew Oxygensensors, before one was working correct.

Hi Gunter,
the fact the oxygen sensor was swapped would rattle my cage instantly. It means someone worked already on the car, did it run nice in the time you own it? 
And, it's got to be the correct one. Not only the correct manufacturer. There's too much bad stuff out there.
But, if you made an appointment already, let's wait and see what happens. 
cheers, good luck, Werner

Hallo Werner,
Hallo Andres, nice to meet you, and thank you for contributing in this thread.

I didn't check this before, but when the engine is cold, the problems of poor running are "almost" not present. When cold, and pressing the throttle, the engine does rev up a lot better. I can still hear, or I think I hear, a bit of misfiring, but I'm not sure.

Regarding the O-2 sensor;
I do know that the O2 sensor directly impacts the EHA valve's function. (through the ecu) is that correct?

Would a fautly O2 sensor cause very lean running? (mitigated somewhat when the engine is cold, through other parameters). And then, when the engine is warm, can the O2-sensor lean out the mixture (by telling the ECU/EHA that the mixture is very rich?) to a degree that the engine does not get extra fuel when revving?
When I visited technical control (tuv) CO measurement was very lean!! 0,1% if I remember correctly, but somehow I consumed 20liters per 100km and more! even when driving gently. How can that be???

Can I trick the ECU in thinking the engine is still cold?

Werner, you said to be sure the correct O2-sensor is installed. So, can you direct me to a good source?

Also, I can see the sensor on the exhaust, but where does it plug in? I can see the line disappear in the chassis, but I can not find the plug, where it connects to the wiring-harness.

MfG

Gunter

Sorry, Andreas, not Andres

Of course...if there is a faulty o2 sensor the engine leans out. Even the exhaust rises to very hot temperatures. When engine is cold, the Sensor is off. That is the reason why your engine runs better when it is Cold. By the Way...the groundsetting  ist probably not ok...That causes the missfiring.
the connector of the sensor is inside the Chassis on the right side in the footwell

Andreas,
I did on several occasions get a "exhaust temperature" warning light. That does point to hot exhaust gasses, lean mixture burns hot, no?

What do you mean by "groundsetting?" Ground of the O2 sensor?

To get to the plug of the O2 sensor, I have to remove the black plastic liner inside the passenger side wheel-housing? This is what you mean by "footwell?" Or do I reach it from inside the cabin?

MfG

Gunter

By the way, Andreas, If I unplug the O2-sensor, but leave it in place, would that be a method of checking if the mixture "holds" (does NOT lean out) when the engine is hot?

MfG
Gunter

Exhaust Temp ist bei Japanern ein Grasbrandsensor und hat mit dem Motorlauf direkt nichts zu tun. wenn der Sensor anspricht dann ist vermutlich der KAT zerbrochen und verstopft den Auspuff, war bei mir auch so. Daher die Überhitzungsmeldung