M111.960 Occasional Stall When Cold

[RoundOzBenz]

Hi,

I have been an avid reader of posts on this forum for a year or so now and have been able to resolve various minor issues with my beloved W124 E220 (M111.960) - thanks to all the members out there. Time for my first post to the board...

The car has been immensely reliable over the years, save for a voltage regulator fault which cost me a new battery, alternator, comfort module and an obscenely botched repair job (which I resorted to rectifying myself). Anyway, that is another story.

The problem here, and I have read nearly all the related posts is the old issue of stalling/idling issues for the M111. I built a fault-code reader as described here, and received two pulses from the HFM system indicating one or more of the following:
- Engine Coolant Temperature Sensor - Short Circuit
- Engine Coolant Temperature Sensor - Open Circuit
- Engine Coolant Temperature Sensor - Signal Incorrect
- Engine Coolant Temperature Sensor - Intermittent Contact

That led me to the three sensors mounted under the plastic shield at the front of the engine (see photo).

All three are negative temperature coefficient sensors, based (partly) on a workshop manual I have, as well as looking up the equivalent replacement parts in a decent automotive sensor supplier's catalogue.

My problem is, other than this I have no further reliable information regarding resistance values over the temperature range. Unfortunately the manual I have is somewhat contradictory, and I think that each respective sensor may have different resistances for the same temperature (though I could be wrong). The manual I have, only offers the temperature curve which I have attached (source: W124 Workshop Manual, LBI Technibooks), and it is vague about which sensor(s) this curve applies to.

Starting at the sensor on the LHS and moving to the right, I took the following readings:
Sensor 1 (LHS)
Cold 400 ohms at 25 degrees C (in Queensland 25 is as low as it gets in summer)
Hot 590 ohms at around 70 degrees C.

Sensor 2 (middle)
Cold 0.5M ohms at 25 degrees C
Hot 125 ohms at around 70 degrees C.

Sensor 3 (RHS)
Cold 5k ohms at 25 degrees C
Hot (didn't take a measurement at the time).

First reasoning instantly point to a fault with sensor 1 since the range is very narrow, but even more importantly it is not reacting like a negative temp coefficient sensor ought to. I.e.: the resistance actually increased with temp, but it is supposed to decrease.

Any thoughts guys, or am I simply incorrect about temp sensor 1? Perhaps it is a positive temp coefficient sensor?

I'm hoping I don't have any issues with the dreaded engine wiring harness or loom. Apparently the insulation on the loom is made out of used teabags from what I gather... another thing to inspect.

Thanks for any help!

 

[samir96]

im having the exact symptom, Stall When Cold....
i haven't measured the resistance on the sensor, im still in the begining of the troubleshooting.

im really intrested with what you've ended, and what did you do to fix the issue...

 

[RoundOzBenz]

The CTS was indeed faulty. Replacement yielded a much smoother and responsive engine. It seemed to slightly reduce the tendency to stall when cold.

My thoughts are that the issue is not a direct cause of any one particular thing. Rather, it's a combination of things that all add up to cause the issue.

Could be the following things, which I am working through:
- faulty engine wiring harness
- any faulty sensors
- vacuum leaks
- poorly lubricated throttle linkages
- dirty intake manifold
- degraded lube inside electronic throttle actuator

I discovered that the engine wiring harness on my car had already been replaced. So I could rule that out.

I used a OBD reader plus software to view live reading of data from the car. I believe I can rule out any faulty sensors, as they were all showing reasonable data. Only sensor I couldn't read was the cam sensor, as the software didn't allow it. I have not disregarded this, but I don't like replacing things that aren't broken.

I found one seemingly minor vacuum leak where the engine was drawing in unmetered air constantly, through the charcoal filter. I disassembled the control valve, cleaned, re-lubricated, and tested. I have now not had the engine stall, unless I place it into gear within around 5-10 seconds of starting. If I leave it to sit for about 10-20 seconds, all good. So definitely onto something there. I'd recommend a full check for vacuum leaks.

I did a quick clean of the intake manifold - no noticeable difference.

Am yet to lube the throttle linkages, though the car has been regularly serviced by MB so they probably aught to be doing this. Inspection of linkages shows that they look fine, no obvious play or friction so unlikely to be an issue.

Throttle actuator - I'm in the process of dismantling anything in the car, degreasing and re-lubricating. The wiper mechanism was in need of serious attention. The mirror actuators were ok but stiff. Throttle actuator is probably in similar condition to the mirror actuators, but worth a look even as a bit of preventive maintenance.

Have patience, lay out a plan, test one thing at a time and don't break anything! Also, when replacing sensors, don't skimp on non-OE/OEM.

 

[samir96]

The CTS was indeed faulty. Replacement yielded a much smoother and responsive engine. It seemed to slightly reduce the tendency to stall when cold.

My thoughts are that the issue is not a direct cause of any one particular thing. Rather, it's a combination of things that all add up to cause the issue.

Could be the following things, which I am working through:
- faulty engine wiring harness
- any faulty sensors
- vacuum leaks
- poorly lubricated throttle linkages
- dirty intake manifold
- degraded lube inside electronic throttle actuator

I discovered that the engine wiring harness on my car had already been replaced. So I could rule that out.

I used a OBD reader plus software to view live reading of data from the car. I believe I can rule out any faulty sensors, as they were all showing reasonable data. Only sensor I couldn't read was the cam sensor, as the software didn't allow it. I have not disregarded this, but I don't like replacing things that aren't broken.

I found one seemingly minor vacuum leak where the engine was drawing in unmetered air constantly, through the charcoal filter. I disassembled the control valve, cleaned, re-lubricated, and tested. I have now not had the engine stall, unless I place it into gear within around 5-10 seconds of starting. If I leave it to sit for about 10-20 seconds, all good. So definitely onto something there. I'd recommend a full check for vacuum leaks.

I did a quick clean of the intake manifold - no noticeable difference.

Am yet to lube the throttle linkages, though the car has been regularly serviced by MB so they probably aught to be doing this. Inspection of linkages shows that they look fine, no obvious play or friction so unlikely to be an issue.

Throttle actuator - I'm in the process of dismantling anything in the car, degreasing and re-lubricating. The wiper mechanism was in need of serious attention. The mirror actuators were ok but stiff. Throttle actuator is probably in similar condition to the mirror actuators, but worth a look even as a bit of preventive maintenance.

Have patience, lay out a plan, test one thing at a time and don't break anything! Also, when replacing sensors, don't skimp on non-OE/OEM.

I have pulled trouble codes from the ECU, on pin 8 just 1 dim blink -> no malfunction in system.

How can I see live data, do you the name of the software / drvice / computer thst can tell libe data?

Regarding wiring harness, its still from the factory, PO didn't change it with the updated one.

Regarding vacuum leaks, can you upload some pictures odd all the vacuum lines that I neese to check ?

Thank you.

 

[RoundOzBenz]

For live data, check this post: HFM Scanner Software by Misha - PeachParts Mercedes ShopForum

I wouldn't make that a priority though as your car doesn't show any faults as you say.

Regarding vacuum lines, this is some research I also need to do myself also. You could take the car to a shop that has a special tool for finding any vacuum leaks. Some places use some kind of smoke machine to do this. There are some other techniques mentioned on this forum.

Forgot to mention, I also pulled the injectors and sent them away for cleaning. I didn't notice any change, but then again all the preventive maintenance I've been doing has improved the stability of the engine in the first few seconds after a cold start.

Another thing I want to check is the fuel pressure.

Keep us posted on your progress.

 

[samir96]

For live data, check this post: HFM Scanner Software by Misha - PeachParts Mercedes ShopForum

I wouldn't make that a priority though as your car doesn't show any faults as you say.

Regarding vacuum lines, this is some research I also need to do myself also. You could take the car to a shop that has a special tool for finding any vacuum leaks. Some places use some kind of smoke machine to do this. There are some other techniques mentioned on this forum.

Forgot to mention, I also pulled the injectors and sent them away for cleaning. I didn't notice any change, but then again all the preventive maintenance I've been doing has improved the stability of the engine in the first few seconds after a cold start.

Another thing I want to check is the fuel pressure.

Keep us posted on your progress.

Yeah I have already changed the injectors.

Regarding vacuum leaks, I will try ti find a near shop who can check vacuum leaks, and see if there's any leaks....

 

[RoundOzBenz]

Any updates on the vacuum check?

 

[mbenz1]

I found this PDF document (click on link below) posted in a USA M-B forum, whilst searching for some MB fault code advice on the net. I know it talks about a W124 model and the old code reader system in that model (somewhere), so maybe it can be of some help to you

http://www.mbslk.com/files/artikel/r170_fehlercodes.pdf

Good luck.

 

[Dieselman]

For vacuum leaks, don't discount the injector O rings.

The fault of intermittent stalling when returning to idle could be vacuum related, but I doubt the one of stalling just after cold start is as the throttle should be slightly open allowing additional air in to create the fast idle. In itself, this reduces issues caused by vacuum leaks, which are most noticeable when the engine is hot, due to the higher vacuum.

Have you tried using a vacuum gauge and a can of plus-gas, or similar, to test for leaks into the intake system?

Stalling when cold is likely to be either, too slow "fast idle" or weak mixture.

 

[RoundOzBenz]

Another follow-up here, and on the same theme that a car approaching 20 yrs of age, will have more than one thing wrong with it.

I checked the resistances on the spark plug (high-tension) leads. The readings were changing between 0 - 30k ohms whenever I moved the cable around. On closer inspection, the leads at each end, screw into the connectors on each end of the cable. I discovered that most of these connections were loose, and the cable could freely turn. All that was needed, was a quick turn to tighten them all up which brought the resistances back to a study 0 ohms. This actually did fix up some occasional lumpy idle issues (whether engine warm or cold).

 

[aghajaved]

i know this is off the topic. but any advice is appreciated. i have a w124 e220 with m111.960 engine. recently i ran a compression test and the figures are 8.5 bars in almost all four cylinders. as the gasket replacement is also due i am thinking if the rings and pistons also need to be changed. i dont know if this compression of 8.5 bars is ok or not. there is a mechanic who suggested me to resleeve and the resleeve he suggested is by inserting the new thinner sleeves within the existing sleeves. this way the sleeves dont need to be taken out and just need to be bored to accomodate the new sleeves. i mean this is sleeves within sleeves. i am not confident. first the compression specifications are unknown and second i dont know what effect it is gonna be as far as heat conduction is concerned if new sleeves are installed within existing sleeves. by the way there is no smoke visible in the exhaust

 

[RoundOzBenz]

Aghajaved, I don't have the workshop information system on hand to look up any spec, but perhaps another member could. You'd be best posting a new topic I'd say.

Regarding your engine, it all depends on how many km you've done, the conditions under which the engine was operated, oil change frequency, etc.

 

[aghajaved]

ok.
thanks. i will be starting a new thread and posting the photos of my rebuild also