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1991 S600 Japanese market
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Discussion Starter #1
As it's sunday and I'm taking a day off from major work on the S600, I was playing around under the hood to see if I could resolve a small roughness to the engine.

I found the spark plug boot on the #12 cylinder was cracked and arcing to ground. I had brought some back with me this summer, so I was able to replace it.

After confirming all the plugs are firing, I was testing the injector firing with a new Noid I brought back. All cylinders were firing fine. I have previously pulled all the injectors and had them tested and cleaned in the states.

My exhaust was still smelling a bit rich. So, I decided to check the Lambda duty cycles for each bank through the diagnostic port. The right hand cylinder was right at 54%, and cycled about 3% when revving the engine.

THe left bank however, was stuck at 79%, and never varied.

I have replaced both O2 sensors with new Bosch ones. I am assuming they are both working correctly. I have traced the wiring from the lamda sensor to the LF injector harness, and have good continuity. The O2 sensors were the type that had to be rewired. They have been soldered and heat shrinked.

The MAFs were taken to the states so I could clean them with proper cleaner (can't get it here). I have checked the supply and output voltage to the MAFs and confirmed they are correct.

So, what am I left with?

1) the new O2 sensor on the left bank is defective OR
2) one of the fuel injectors on that bank is not closing correctly.

Any other thoughts on what might be affecting the Lamda reading?


Cheers
 

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1991 S600 Japanese market
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Discussion Starter #2
After a bit more sleuthing, I came across a tidbit from K6JRF pages.


When testing the lambda ration on the X11 socket, with the ignition on but the engine not running, I get a reading of 50% duty cycle. That is normal.

When the engine is run between idle and 2500 rpm, the duty cycle goes to 79%. According the his diagnostic table, that indicates either:

1. TN signal
2. CAN data

I have cleaned and tested the connectors and bus signal, so I am going to discount the CAN data problem.

If this is a TN signal problem, that would indicated the crankshaft position/speed sensor.

However, if that piece is defective, would that not show up in other rather severe aspects of engine performance?

Then engine is running very nicely, except for the fuel mixture being excessively rich (as indicated by the plugs and the exhaust smell).

Have other members have this sensor fail? If so, what were your symptoms?

Cheers
 

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600SEL
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LH computer needs very long time and mileage to re-adapt mixture. If you just replaced defective boot on a spark plug give it some time and check again. Even better, if you had access to Mercedes scanner check adaptation values and see if any were at the limit. It should trigger CEL, but your car may not have it.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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if crankshaft position sensor is bad then the engine will not start. i guess no one knows what happens if this sensor is "conditionally bad", for instance if its wires are damaged or if electrical disturbances affect its signal into the EZL module. maybe this is your case (in addition what myarmar suggested) but i doubt it is. BTW, re-adaptation can take several weeks at every day driving ... in these cars.
 

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1991 S600 Japanese market
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Discussion Starter #5
Guys,

Thanks so much for this feedback. I'm looking for an excuse not to go swap the O2 sensors right now. Got enough other things to attend to on the car.

It's good to know about the adaptation time. I wish I could pull the codes off the LH computers, but there are no diagnostic tools out here for these early models. Even the code blinker I built does not work.

Samosali: I was wondering about the crank position sensor. MB of Naples has them listed for $60 each. Given how critical they are, I think it would a wise idea to get them out here. As simple pulse counters, they are suseptible to aging, esp in a hot environment (driving an S600 in the desert in South Sudan is about as bad as it gets!).

As to the EZL: I was under the impression that the signals went to the LH computers, then to the EZL. I'll have to check out the wiring diagrams.

Myanmar: Your correct. There is no CEL on this car. It's a Japanese market model.

After I get the kick down/throttle cable hooked up properly to the trans, I'll start road testing it. I drove it about 50km yesterday, and thought I noticed a change for the better. That could also be wishful thinking.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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Samosali: I was wondering about the crank position sensor. MB of Naples has them listed for $60 each. Given how critical they are, I think it would a wise idea to get them out here. As simple pulse counters, they are suseptible to aging, esp in a hot environment (driving an S600 in the desert in South Sudan is about as bad as it gets!).
$60 each? this must be a mistake. first the price should be much higher and second i believe there is only one sensor. Look, my car has m119 engine with one sensor and i expect that any machine in the world has only one crankshaft position sensor. But i do not know for 100% sure of course ... i did not design any of these engines :).

Signal from crankshaft position sensor goes directly into EZL module and nowhere else. the core wire and shield wire (minus terminal i guess); two wires into one cable.
 

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1991 S600 Japanese market
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Discussion Starter #7
I know. The price is about 1/3 of what I've found elsewhere. But here is the listing:

Mercedes-Benz. #0031531928: Engine Crankshaft Position Sensor. Right; Optional

Looking at the wiring diagram, it is clear that the CPS goes into the ignition computer. The M120 engine has two of those computers,
hence the need to 2 of the sensors.

Tempted to put a scope on them and see what happens...


Cheers
 

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86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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My experience with crank position sensors is that they are pass/fail. Put a meter on the EZl end and measure your residence. If it shows anything above 650 ohms, you're good.
 

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1991 S600 Japanese market
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Discussion Starter #9
Jayare,

Thanks. That's a useful piece of info.

And an explanation of why the LH might take weeks to adapt:

"After doing the adaptation a few times, it became apparent why it took so long on the
street. The program requires achievement of a certain condition: Load 40-80kg/hr; rpm
1,600-2,200. Once stable at that condition (easy to achieve on a dyno), the car's
adaptation program goes active and it requires holding those conditions for maybe 10
seconds in lower partial. If you try to recreate these conditions on the road, it's almost
impossible except when driving against exactly the right angle hill. At the load stated, the
car accelerates unless it's on the right-size hill and quickly exceeds the rpm criteria,
stopping the adaptation process."

From an LH diagnositics paper I found.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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so m120 actually has two crankshaft position sensors? i guess the other one detects exactly the same signal as first one because m120 has one crankshaft :) ?

In my car the signal goes from the sensor into EZL module, it can also be called ignition module. It is on the left fender. i guess you have two EZLs (ignition modules)? Or the signal goes directly into the computer box under the hood ... i do not think so but now i am confused. v12 is nothing more than V8 with 4 cylinders more :)
 

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so it really has two crankshaft position sensors?

P.S.: holy molly, i checked in EPC and there are two sensors indeed. i should be quiet ... now someone tell me that signal from it (them) go into computer box instead into EZL module(s). ????
 

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1991 S600 Japanese market
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Discussion Starter #13
Samosali,

Sorry. Each sensor goes into the ignition computer on their respective sides of the car.
 

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so it really has two crankshaft position sensors?

P.S.: holy molly, i checked in EPC and there are two sensors indeed. i should be quiet ... now someone tell me that signal from it (them) go into computer box instead into EZL module(s). ????
Yes indeed, Sir.
And their location -- OMG -- unless you have the top of the engine (or the transmission) out of the way, I see no way to change them.

Some pictures and useful info (with cross-referenced part numbers) here:

http://www.benzworld.org/forums/w140-s-class/2562641-m120-crankshaft-position-sensors-2.html#post13787009

Best regards,
Steve
 

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1991 S600 Japanese market
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Discussion Starter #15
Steve,

Your are right. They are a PITA to get out. I've pulled the intake to refresh it and put new gaskets; PCV, vacuum lines etc. while I was in there. I could see that it was easy to get to the sensors while all that was out of the way.

Jayare: Mine are measuring 890 ohms each, so I"m going to assume they are fine and leave them at that. I may grab a set just to have in my spares box though.

Cheers
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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Steve, scottpeterds, thanks for clarification. And thank you scottpeterd to spare at least some shame to me :) because you confirmed that signal goes directly into EZL module which is called also ignition module. So at least this is same in comparison to M119. Sorry once again to try to convince you that M120 has only one sensor. Ahhhhhh......
 
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