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

Hi everyone,
It's difficult to make a good start for a problem that has me scratching my head, and negatively affecting my sleep...
When I aqcuired the SL, I noticed some hesitation in the engine at WOT (wide open throttle). The SL ran ok (but not TOP).
Cold and warm starts were very good, idle was stable, well for 90%, but fuel consumption was and is very high at 20 liters per 100km, even when driving with an egg under my right foot.
Acceleration was becoming more and more problematic, at one instance, the car would not rev past 4.000rpm, and "bogged down" when pressing the gas-pedal.
At this moment, I can start the SL, but I cannot rev the engine. Only at cold start, it will rev (a bit) when gently pushing the gas-pedal, but when warm, again, I cannot get the engine to rev.
It is hard to type a "sound" but when I try to rev, the engine sound a bit like "beuhhh."
What I have done, up 'till now, related or not;
1. replace vacuum modulator on the transmission
2. new oil-pan, new oil-filter, new oil, and new oil-seal for the transmission (still leaks ), bolts torqued to 8nm, star-wise pattern
3. new bushing on the transmission
4. new bushing on the differential
5. new oil and filter for the engine
6. new fuel-pump switch
7. new steering damper

At one instance the car just went DEAD. By pure chance, I found a small short-circuit in the coax-cable coming from the crank-shaft sensor. At that time, I took the car on a 500km trip, with no issues (other than that small reluctance to rev-out at WOT)

Now things get interesting;

8. I changed out the 2 small O-rings from the "EHA" valve, between the valve and the fuel-distriburtor, and the problems got very bad at that time, so no more revving the engine. Idle is lumpy, and to low at warm-up. Car does start reasonably well.
9. removed fuel-pumps, accumuator, filter, and screen filter, and removed a lot of "fluid-rust" from inside the tank. Replaced with new pumps, filter, accumulator, screen filter, fuel lines. Cost; 1400eur Problem was NOT solved.
10. Measured pressures al fuel distributor; 6,2bar working pressure, 6,2bar controled pressure (?????). Screwed in the control-screw in the EHA valve (under the brass security-screw), car would NOT start, although pressures were still at 6,2bar. EHA started leaking externally.
11. Ordered a new EHA valve, cost, 480eur. Problem was NOT solved.
12. Measured control-pressure, now at 6+ bar, when pressing gas-pedal, pressure fluctuated, when engine was cold, more stable when warm.
13. Noticed a leak at a fuel-line, under de driver-side rear-wheel, a line with a rubber extenstion, and only attached by a clamp, so I presume, return-line to the fuel tank.

And here we are today. 4 months later.

Questions;
1. would a blocked return-line to the fuel-tank trigger a higher-than-normal control-pressure at the fuel-distributor?
2. could a blocked return line be the cause of the unwillingness of the engine to rev?
3. what is de best procedure to check and remedy a blocked fuel line?

any and all help is much appreciated!



 

Hi Gunter,

consider it a NO GO to touch EHA's adjustment screws. Please keep the new one as it is.

Please check that you now have a lower chamber pressure of 6.2 -0.4 = 5.8 bar when you remove connector on EHA.

A blocked fuel return line can increase upper and lower chamber pressure above spec values. But I would expect more than 6.2 bar upper chamber pressure then. But you can do an easy test. Put a bucket besides engien and let return fuel go into that bucket. If engine suddenly runs well, you know that there is a problem with reutrn line.

Dr,
Yes, I have learned that the adjustment-screw is not for adjusting, but serves a means for Bosch to calibrate the EHA for different engines.
So much for the information on youtube.....
I forgot to detach the plug on the EHA when measuring the lower-chamber pressure. Will measure again this evening.
I will take up your suggestion regarding catching the fuel from the return line.

But that ads a question; there a more lines under the SL than simply supply an demand. Is there a schematic available?

Hi Gunter,

just call me Volker please.

On fuel distributor you only have incoming line, line to 8-cylinders, outflowing line with fuel pressure regulator and line to cold start valve.

Hi Gunter,
did you check the emissions? If the motor runs way too
rich it should smoke and smell from the exhaust. Also the oillevel in the engine could rise, and the oil possibly smells for gas too. 
For some reason I think your car runs partly too lean, and party too rich. 
What's the mileage of the car/motor? Maybe your cold-idle injector is acting funny, or your injectors are worn. I had something comparable on my 560, and 3 injectors were just dripping and not spraying anymore. 
Take out the sparkplugs and look at them, if these are wet, you know where to start tracking. 
all the best, cheers, Werner

Dr.
I will call you Volker, then.
I will make some pictures for further clarification if the need arises.
tx!

Herr Werner,
1. At the technical control office, CO measurement was VERY low (at idle)
2. Doesn't smell of fuel, and only smokes "water-vapor" at coldstart. No black fumes when accelerating (when it ran, of course)
3. I recently changed the oil, and viscosity seems ok, also, oil does not smell of fuel
4. The SL has about 85.000km. Service history from Japan is missing, but from 2010 onwards there are a lot of invoices
5. Well, for now it is a bit of a guessing game, but I am taking this step by step. Can't say if it is de cold-start injector, or the idle air-bypass. When I did measure operating pressure, the gauge held at about 3 bar for more than 30 minutes, so the system in itself seems "tight."

Hi Gunter,
please let us now the readings of the emmission test. If it's really low it would possibly confirm what I thought. 
thanks, cheers, Werner

Hello Gunter,
have you already checked this "often forgotten" small filter  in front of the gasoline distributer. It is mounted as a connection fitting made in brass between end of gasoline pipe/hose and entrance of distributor. It is not obviously recognizable as a filter.
Greetings Philipp

Hallo Werner,
I am unable to perform a new emissions test at this moment, but at idle, it most certainly is not "rich."
MfG
Gunter

Hallo Philipp,
Yes, the small inline filter in the feed-line to the fuel-distributor has been changed.
The big filter at the pumps has also been changed, AND the screen-filter on the underside of the tank has also been changed.
But all this did not resolve the problem.
MfG
Gunter

So, to continue the saga;
A few days ago, while performing some pressure-measurements on the distributor, I noticed a fuel-leak on the return-line, from the distributor to the tank.I read a control-pressure of 6,1bar, so I figured that there could be a blockage in the return-line, in the tank.
Elsewhere, I read that something like this sometimes happens.
When removing the rubber part of the return-line, the clip holding it, just desintregrated. It fell of. I then could easily remove the rubber part after clamping it of to prevent fuel leaking out of the return line from the tank.
I then placed a hose on the return line, and directed it to a bucket.I started the car, and a steady stream (with a lot of bubbles!) came through the feed line, to the bucket.
At first I thought that the engine ran better, but it was not the case when it warmed a bit.I then removed the clamp on the rubber part of the return-line, still attached to the tank, and nothing came out! Bone-dry! Not even a drop of fuel.

I then placed my air-gun on the rubber-line, and applied 0,75bar of pressure, and I immediately heard bubbles in the tank, so no blockage of the return-line to the tank.(I presume there is a one-way valve between where I applied air-pressure and the entry in the tank, because no fuel came out. Is this a correct assumption?)I then re-attached the rubber to the return-line, with a new clamp, to prevent further leakage.I

then re-attached my pressure-gauge to the distributor, to measure working and control-pressure. (EHA-valve unplugged!)I read a working pressure of 6.2 bar, and I read a control pressure of.... 6.2 bar. When opening the valve, to measure the control-pressure, the engine almost died, but it picked up again.When opening the valve on the pressure-gauge, the needle of the mano-meter DOES NOT MOVE at al.So the pressure in the upper and the lower chamber of the distributor is exactly the same, and doesn't even change of move the needle on the mano-meter when opening the valve on the pressure-gauge.

I really don't know what to make of this.

I slightly changed the initial opening of the air-flap, idle was steady at about 750rpm (neutral, no AC), but applying throttle was not possible.

Questions;
Is it normal that the fuel coming through the return line contains a lot of air bubbles?
Is there a one-way-valve on the returnline, somewhere in the trunk? (not visible?)
What to make of the fact that working and controlled pressure of the fuel distributor is exactly the same? Can I conclude that the is a leak between the upper and lower chamber?

Some pictures;


MfGGunter 

Hi Gunter,

if lower chamber pressure with new EHA is the same as upper chamber then there are 4 possibilities:

1. Fuel cannnot flow back to tank - you checked that and I already wrote that I would then also expect a too high upper chamber pressure.
2. New EHA is broken - Doubtful
3. Throttle opening inside fuel distributor is too wide open and lets too much fuel to lower chamber. EHA cannot compensate by releasing fuel to tank.
4. You measure wrogly.

Of course engine cannot run when you use 3-way valve for measuring and open that. That is what floods lower cahmber with fuel and EHA cannot compensate.

Hi Volker,
1. It is safe to say that "flow" is not an issue. Although the return-fuel had a lot of (air)bubbles in it.
2. Or both EHA's function correct (and cannot compensate for deeper lying problem) or they are both broken. I must assument the first of course, because problems were exactly the same before and after installing the new EHA.
3. How could the throttle-plate become "incorrect?" I did not touch it. You DO mean the throttle-plate which is attached to the potentiometer?
4. I also measured pressure, only at the "lower-chamber" check-valve, (after installing new EHA) and read 6,1bar with some fluctuation when trying to rev. There are different set ups and examples, so I cannot be absolutely sure I measured correctly.
I attached the line with the on/off valve to the cold-start line, then to a T-piece for attaching the mano-meter, and then from there to the other side to the check-valve (covered with the 12mm bolt). When the on/off valve was closed, pressure was at 6,2bar, and after opening (engine almost "died" but then picked up again) did not move at all. (so 6,1bar when only measuring at the lower-chamber check-valve.)

This is getting confusing, no?

Hi Gunter,

1. I do not understand where many bubbles would come from.But you are on the pressureless side
2. I guess that your new ECA works well
3. It is not the throttle plate. It is a throttle hole that limits the amount of fuel thant can go inside Fuel Distributor from upper to lower chamber. Otherwise EHA has no chance to reduce lower chamber pressure.
4. YOur manometer must be on the side of testing screw in lower chamber. Valve must be between manometer and coldstart line on upper chamber. If you  measure pressure of cold start line, it will always be system pressure. When you open valve you flood lower chamber with so much fuel that EHA cannot reduce lower chamber pressure. Result will be dying engine.

That is why I never user this setup with oen manometer and 3-way valve. I always connect one 10 Bar manometer to coldstart line to measure system pressure. And another 6 Bar manometer to test screw opening of lower chamber. Then you should see 0.4 Bar lower pressure in lower chamber if EHA is disconnected. Or you measure current into EHA. Should be around 0 for idle-run.

Seems like I have to translate my K-Jetronic manometer article to English as well.

Hi Gunter,
are you sure there is enough fuel in the tank? Bubbles in the backline is not normal. EHS cannot regulate gas bubbles under pressure only liquid. Fill up with 10 liters of petrol and test again. Perhaps the swirl pot in the tank is damaged and there is not enough fuel in the tank, in this case the pump is sucking air and you have bubbles inside the distributor and in the backline, don't believe the fuel gauge instrument

Hello Igor, thank you for your contribution!

Well, the problems with fuel delivery are irrespective of the fact there were bubbles in the returnline. When the issue first occurred, there was about 40 liters of fuel in the tank.
But it is true that when I removed the rubber part of the return-line there was only a little bit of fuel in the tank.
MfG
Gunter

Good morning, Volker,

It seems we are trying to kill mosquitos in the dark. If you hit enough, you certainly will kill some, but it is not very efficient

Last night I have been reading some technical information on the K- and KE-jet systems, and I now understand that the base of the system is the pressure provided by the pumps, at 6,2bar, and the exit through the injectors at 3,8 bar. (less, if the injectors are worn)
Even if ALL electrical "adjustments" are removed, the system should still provide the 6,2bar working pressure to the distributor (whose main task is to provide EQUAL AMOUNTS of fuel to the injectors, under different kinds of conditions.)
It is the pressure "differential" of 0,4bar (6.2 to 5.8 in my case) that opens the diapgragm between upper and lower chambers and "lets through" fuel.
Applying "throttle" moves the plunger in de distributor, to increase the amount of fuel.

So, I measured (single line) 6.2 bar at the cold-start line, and I measured 6.1 (single line) bar at the check opening. (so measured, NOT with the 3-way valve!)

So instead of a differential of 0.4 bar, I only have a differential of 0.1 bar. So instead of too much fuel, I am not getting enough fuel!
Stepping on the gas, depressing the plunger in de distributor does NOTHING now, because the pressure-differential of 0.1 bar, does not "allow" this increase in fuel to flow through to the injector lines.

Which DOES explain that "on-idle" (idle uses a metered hole, not the upper and lowers chambers, to get fuel) the car runs "ok-ish" but once the pressure-differential is needed to send fuel to the injector-lines, everything goes wrong.

Am I correct in my theory?

MfG
Gunter

wie sieht dein Tank von innen aus, schau mal in den Tank durch die Öffnung des Tankgebers, dazu benötigst du eine 46er-Nuss.
Wenn da alles klar und sauber ist dann ist es ok, sieht es da trüb aus, dann kommt zwar der druck aber nicht die nötige Menge.
 

Hi Ragetti
I replaced the tank-screen-filter (I used a dremel to enlarge the chassis-hole, because the screen was not "centered" and then it came out, together with the feed line, so I was lucky ) and replaced the complete pump-assembly. (so 2 new pumps, new accumulator, new filter, new lines, new brackets, etc.)
There was a lot of rust that came out together with the screen filter, and I then used a tooth-brush, bent to 90°, to clean out the "whirl-pool" inside the tank.
So I must assume that pressure AND flow is sufficient.

See my message to Volker; the pressure-differential in the distributor is TOO LOW (only 0.1 bar, separate measurements)

Working pressure is 6.2 bar, control pressure is 6.1 bar.

How do I get the control pressure DOWN to increase fuel-flow?

Thanks for the help!
MfG
Gunter