w124 m104 rough idle stalling and not shifting gears help

[lucian25]

Upon further inspection of my automobile i have noticed the following:

- with the air filter off and the car running i proceeded to remove the vacuum lines connected to the manifold one by one. Upon removing the line that connects to the gearbox and goes under the car the idle sounded the same with or without, it only changes when i put my finger over the manifold and the engine seems to settle down a bit, bareley noticeable but a difference nonetheless.

 

[lucian25]

- got hold of a multimeter and measured the coolant temperature sensor resistance. It has 2 pins to witch i connected the device set to resistance. When the engine was cold it showed 17 Ohms and when i got it to 80 degrees C (dashboard reading) it measured 0.6 Ohm. According to the chart from this post, these numbers are off: (scroll down the cts is there too)
http://www.benzworld.org/forums/w12...intake-air-temperature-sensor-resistance.html

I also measured the voltage of the plugged in connector by connecting the negative of the multimeter to the battery - and the positive to one of the connector wires like this:
http://www.tiepie.com/en/automotive/Measurement_examples/Sensors/Coolant_Temperature_Sensor

It showed 5 volts with cold engine and when it started to heat up dropped to 2.98 at 80 degrees. It is my understanding that this number should be lower is that correct?

 

[lucian25]

Could these be my problems? The vacuum line to the gearbox that prevents changes and the out of spec coolant temperature sensor that sends false readings to the ecm preventing the car from going in to closed loop and therefore running poorly when hot?
I would like to mention that i have tried adjusting the duty cycle with the engine running for 30 minutes and was unable to make any changes. Is it true that duty cycle can only be adjusted when the engine is in closed loop?
And if anybody knows at what voltage does the cts trigger the ecm to go in to closed loop? Maybe somebody could test their sensor in closed loop and tell me a volt reading. Much obliged.
PS: sorry for spacing out like this but i can't seem to post it all at once it's weird

 

[grober]

Your poor running when hot might be caused by a weak mixture due to manifold leaks. When the engine is warming up the mixture will be rich to improve idle---- after it warms up the weak mixture symptoms will show up. If your gearbox actuator is leaking then if you disconnect the connection at the manifold your engine will idle and driving should improve- the gear changes will still be bad but ignore them for the moment. If things improve engine wise you have possibly found one leak- but there may be others. You really need a vacuum tester to check out these lines correctly.

 

[lucian25]

Can a clogged fuel filter cause weak mixture?

 

[lucian25]

The distributor cap on m104980 has a spring loaded central electrode as seen in the picture. When i took mine out for a clean this central electrode was barely sticking out.
Common sense tells me that this is suppose to make contact with the rotor arm in order to provide electricity for ignition.
As i mentioned mine just barely comes out of it's hole, if it was to make a bad contact what would the symptoms be? Would it stall the engine or just make it run rough?

 

[ray_hennig]

The distributor cap on m104980 has a spring loaded central electrode as seen in the picture. When i took mine out for a clean this central electrode was barely sticking out.
Common sense tells me that this is suppose to make contact with the rotor arm in order to provide electricity for ignition.
As i mentioned mine just barely comes out of it's hole, if it was to make a bad contact what would the symptoms be? Would it stall the engine or just make it run rough?

My genuine MB cap central electrode has always been fixed, not spring-loaded type. They've both been like that.

R

 

[lucian25]

My genuine MB cap central electrode has always been fixed, not spring-loaded type. They've both been like that.

R

Now that's weird..
Ok i found the problem, i think it's the fuel evaporator and the regeneration switchover valve, have to do a few tests.

 

[ray_hennig]

Now that's weird..
Ok i found the problem, i think it's the fuel evaporator and the regeneration switchover valve, have to do a few tests.

That's a new one to me on this model of car.

Tell me more, give some details.

R

 

[grober]

That's a new one to me on this model of car.

Tell me more, give some details.

R

Possible major inlet manifold leak in pipework to the solenoid operated valve that evacuates the under wing charcoal filter leading to weak running/ poor vacuum . In turn failure to evacuate the charcoal filter that vents the fuel tank might mean a partial tank vacuum which might impede fuel supply.-------- would be my guess what the tester is talking about --but not sure. Solution/ test--- block off the pipe to the manifold to stop the leak and loosen the tank filler cap temporarily to keep the tank at atmospheric pressure??

 

[lucian25]

It is exactly as Grober said. But upon further tests with the valve disconnected the problem reappeared after a restart.
Ok so i have been doing some reading on the vacuum lines that lead to the manifold and discovered a major one that is overlooked, and that's the brake booster vacuum pipe. It has a non return valve.
So tonight the car was running rough again and stalling and after reading about how the brakes use vacuum to operate, i turned the engine off and proceeded to pump the brake pedal until it got rock hard and restart it. The problem immediately went away and as i pump the brake with the engine running in park mode the rpm rises to 1000 and stays solid. Took it for a drive and the tranny shifts gear.
I'm thinking this vacuum brake line is the culprit, i'm going the check it out tomorrow and see what's what.

 

[ray_hennig]

Possible major inlet manifold leak in pipework to the solenoid operated valve that evacuates the under wing charcoal filter leading to weak running/ poor vacuum . In turn failure to evacuate the charcoal filter that vents the fuel tank might mean a partial tank vacuum which might impede fuel supply.-------- would be my guess what the tester is talking about --but not sure. Solution/ test--- block off the pipe to the manifold to stop the leak and loosen the tank filler cap temporarily to keep the tank at atmospheric pressure??

I'm learning a bit here as I've never thought about this charcoal filter. Why? Because I didn't think I had one.

How do I tell? What signs are there that my 1991 300CE-24 (104.980) has one?

Typically, things are complicated because I'm in Paris and the car's 500 Ks away!! My son's looking after it so maybe he can poke around until I get down there to take a look.

Any pointers, Grober, as to how I can trace this illusive filter? Certainly, if I have one, it has never been changed or otherwise cossetted.

Thank you all for comments so far and sorry to take over this thread.

Best to all.

RayH

 

[grober]

The charcoal filter is hidden behind the nearside wheel arch liner- you have to remove it for access. pic 2 Its evacuated by by manifold vacuum thro a solenoid valve mounted on the wing centre behind the abs unit pic 1 - on older cars its a vacuum operated valve arrangement towards the front of the car still on the inner wing . The tank fumes are absorbed by the filter via a pipe which runs from the tank at the back of the car alongside the brake and fuel pipes. Problems arise if the solenoid valve fails or more commonly the flexible rubber connectors perish. The filter is supposed to to be changed at about 70,000 miles but many are ignored--- some people have no trouble with them but others find leaks affect the idle etc.

 

[lucian25]

I'm almost at the point of giving up on the car. I don't think the problem is vacuum related. Just swapped the battery with a brand new bosch silver and it's still the same, it won't idle properly and won't shift gears unless i turn on all the electrical equipment in the car (head lamps, rear window defogger and blower fan). Maybe it has a voltage leak or something and by turning on electrical stuff i'm drawing more amps from the alternator. Checked new battery voltage with a multimeter and it's in the low 13's, sometimes drops to 12.
Also changed fuel filter, air filter, spark plugs and coolant temperature sensor.
This car is a pice of crap, german engineering my ass!

 

[ray_hennig]

I'm almost at the point of giving up on the car. I don't think the problem is vacuum related. Just swapped the battery with a brand new bosch silver and it's still the same, it won't idle properly and won't shift gears unless i turn on all the electrical equipment in the car (head lamps, rear window defogger and blower fan). Maybe it has a voltage leak or something and by turning on electrical stuff i'm drawing more amps from the alternator. Checked new battery voltage with a multimeter and it's in the low 13's, sometimes drops to 12.
Also changed fuel filter, air filter, spark plugs and coolant temperature sensor.
This car is a pice of crap, german engineering my ass!

Don't give up. The car is, potentially, far from being crap.

There are many small, cheap things it could be.

R

 

[grober]

Get the alternator output checked- its possible its putting out too high a voltage - the regulator pack is easily changed. But maybe its time to take the car to an auto gearbox specialist?? Another possibility is you have a faulty kickdown switch under the accelerator pedal- this might cause electrical problems and also prevent the car from changing up --- the list of possible faults is endless and its impossible to diagnose from a distance - just make suggestions.

 

[lucian25]

DSCF0537 - YouTube

So i have been testing the ht lead from ignition coil to the distributor, i think it is called king lead or something. It shows no resistance at all and the multimeter beeps continuity. It also has a few cracks in the cable.
Is this right? Can a failing main ht lead relate to the symptoms on my car?

 

[lucian25]

Just wanted to let you guys know how it turned out. I did my stupid measurement of the ht king lead and ordered a new bosch one. The part just arrived today and before installing it i though i would measure the new one also. Surprise, it measured the same and no surprise when installed the car run the same. It started doing the rough idling even when warming up.
To say i was completely ****** off is an understatement. In rage i removed the air filter and started pulling connectors randomly with the engine running. When i got to the cold start injector valve and disabled it the engine seemed to run better, the idle was like really smooth and when i revved the engine it didn't die when the rpms dropped.
Put the air filter housing back and took it for a spin. Idle was okay engine sounded fine.. no gear change, except of course when i turned on electrical stuff. Hopeless i thought, and then i remembered i tinkered with the throttle cable adjustment. Stopped the car made a few turns to tighten the throttle cable et voila! Now it idles perfect, it changes gear, goes like a rocket, still has the huge rust hole in the back but i guess nothing is perfect.
So in the end it was the cold start injector and the throttle cable adjustment that were causing the problems. What is the point of that stupid injector?? Other cars don't have it and they do fine without, even in winter at low temperatures. A classic example of german engineering overkill maybe. Can i run the car without it?
Thank you Ray and Grober for your replies, even if you were not on the money it still helps not to feel alone in a sea of incompetent mechanics and aftermarket cheap parts.
Gonna take it for a spin now, hopefully i'll write off a bimmer or something

 

[danandgerry]

Glad your sorted Lucian

 

[grober]

So in the end it was the cold start injector and the throttle cable adjustment that were causing the problems. What is the point of that stupid injector?? Other cars don't have it and they do fine without, even in winter at low temperatures. A classic example of german engineering overkill maybe. Can i run the car without it?
Thank you Ray and Grober for your replies, even if you were not on the money it still helps not to feel alone in a sea of incompetent mechanics and aftermarket cheap parts.

The cold start valve only runs for a very short period of time when the engine is cold. e.g. 7.5 seconds at -20C When cold its timing is controlled via a thermo time switch which operates via a heated bimetal strip "timer" which dependent on engine block temperature. Needless to say when the engine is warm/hot means the switch is off and the cold start valve doesn't operate. When an engine is very cold it presents a series of very cold metal surfaces for fuel to condense out on and this leans the mixture. The cold start valve is supposed to counteract this brief period of fuel condensation long enough for the engine to fire and once started the mixture enrichment/ fast idle units can compensate adequately until the engine warms up fully.
Glad you are back up and running.