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1992 W124 260E
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Discussion Starter #1
I'm a newbie .. Please be gentle..

Some background of the car
Mercedes Benz W124 260E (1992) Right-hand drive
VIN WDB1240262B**
130K+ miles
Purchased 1+ yrs ago

I'm a newbie. So far I have done these (DIY):
1. New tyres + balancing + alignment (shop)
2. Axle gear / Final drive oil (change)
3. Transmission fluid (change)
4. Brake fluid (flush)
5. Engine oil + filter
6. Coolant (flush)
7. New spark plugs
8. Thermostat (check)
9. Ball joint (RF)
10. Battery (new)
11. Fuel Pump Relay (new)
12. Over Voltage Protection relay (new)
13. Fuel filter (new)
14. Fuel Pumps (2 new)
15. Fuel Accumulator (new)
16. Fuel hoses (new)
17. Fuel return valve (new)
18. Fuel tank (removed and cleaned)
19. Cold Start Valve (cleaned)
20. Spark plugs cables (new)
21. Vacuum lines (replaced, some)

Problem started in May 2019 when the car stalled at a traffic light. It started after a few cranks (but rough/jerky) and I managed to drive it home. I started to replace/service all the items from number 10 onwards, thinking the car was 27 yrs old and some parts do need replacement (they were 27 years old!!!). None of the things I did resolve the problem. The car would start ok and after 10 minutes or so or when I switched on the AC, the engine sputtered and stalled and refused to start. If it starts, when I turned the AC again, it will stall. Then, I checked the vacuum lines and found that some of the vacuum lines are old and the rubber hoses are cracked and I replaced them. I also found that the O2 sensor wires (under the footwell) was not connected and reconnect them. The car was running fine without the O2 sensor for the last 1 year plus. Hmmm.

The car started in just one crank but the same problem reoccured. The next morning, I disconnected the O2 sensor wires and let the engine run for 50 minutes (AC off) and then turned on the AC and the car did not stall. Today, it started immediately, after 10 minutes turned the AC on and turned it off again. It did not stall but the idle is close to 1K. Before it was between 650 to 800. I haven’t driven the car so I would not know whether it’s going to stall again or not. I plan to do a smoke test to check the condition of the vacuum lines.... and replace the O2 sensor

Questions:
1. Where can I find a vacuum lines diagram for this car? I managed to get a few for other models like W123 etc but not for this model.
2. Where do I go from here? I plan to replace the O2 sensor in order to adjust the duty cycle.
** I may have wrongly named some of the car parts since I still have difficulty naming them, let alone locating them on the car... LOL. Seriously.... BTW, I need help on this, too.

Any help/suggestion is highly appreciated... Or references/links/...
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,260 Posts
My highest suspicion is that something is causing your OVP to turn off and back on again. Intermittently.
Seems to be somehow tied to (or effected by) your AC as well.
It could be a myriad of things but I would first diagnose the issue before throwing more parts at it.

With the O2 sensor plugged back in, stick a couple of wires into your IACV valve and monitor the IACV voltage inside your car. Secure and run the wires into the car and connect a voltmeter to it. Since you can trigger the stall with the AC, just monitor your IACV voltage. If it goes to zero and back on to a large positive voltage right before it stalls you know your OVP is turning off and back on again and that will stall the engine, every time.

Mercedes has made the OVP turning off (going into limp mode) fool proof successfully..
The OVP turning back on while the engine is idling ........ not so much. They missed that failure mode.

You will still need to figure out why turning on the AC is messing with the OVP. But first make sure my suspicion is on the right track.

- Cheers!
 

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1992 W124 260E
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36 Posts
Discussion Starter #3
Update:
Yesterday, did these:
1. Removed and cleaned the IACV and reintalled it
2. O2 sensor plugged in and carried out the procedure dolucasi mentioned. This is what I found.
  • first 20 minutes, IACV was running at 5.6~5.8V without AC clutch on and 6.2~6.4V when AC kicked in
  • 20-40 minutes, engine started shaking hard when the AC kicked in but luckily did not stall. RPM was lower and oil pressure was close to the 1 mark.
  • 40 minutes onwards, the shaking disappeared and engine ran smoothly, AC on or off.
  • 50 minutes, switched off the engine, waited for a couple of minutes and restarted it and it cranked just once and ran smoothly...
3 hours later...
1. Unplugged the O2 sensor and ran the procedure again...The car ran smoothly for an hour with the AC on as if nothing happened... lol.
I suspect and read in one of Bosch documents on Lambda sensor that there is such a thing as a "slow" rather than 'dead' lambda sensor, thus the shaking/stalling engine because the sensor is slow to do its work... Whereas without the O2 sensor, the engine just goes rich/lean... but hey, I'm the newbie here... Educate me...:)

All suggestions welcomed...
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,260 Posts
It would be helpful if you reported the IACV voltage together with all the bullets you have in your list (not just what the value it was in the beginning)
 

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1992 W124 260E
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Discussion Starter #5
O2 plugged in
  • first 20 minutes, IACV was running at 5.6~5.8V without AC clutch on and 6.2~6.4V when AC kicked in
  • 20-40 minutes, engine started shaking hard when the AC kicked in but luckily did not stall. RPM was lower and oil pressure was close to the 1 mark. AC off 5.7~5.8V, AC on 6.7~6.9V
  • 40 minutes onwards, the shaking disappeared and engine ran smoothly, AC off 5.6~5.8V or AC on 6.0~6.2V.
  • 50 minutes, switched off the engine, waited for a couple of minutes and restarted it and it cranked just once and ran smoothly with close to 40 minutes onwards readings
Without O2,
  • first 20 minutes, AC off 5.5~5.6V , AC on 5.8~6.0V, no shakes
  • at 40 minutes, AC off 5.6~5.7V, AC on 6.0~6.1V, no shakes
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,260 Posts
Those readings all look normal. WIth AC on the IACV needs to open up a bit more for added air (and hopefully fuel).

So it does not appear to be idle speed control related. As a follow on diagnostic one should measure the EHA current under the various scenarios you have above. SInce EHA current is a little harder (as you need to jump one side of the pair from the connector to the EHA valve and put the other wire thru a current meter, alternatively you could be measuring the duty cycle (or voltage) at the X11 connector. Pins 3 to 2 is just the EHA current translated into voltage.

- Cheers!
 

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W124
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Before you do any more part replacement, confirm that the alternator is working properly. You should measure 13.7 to 14.0 v DC across the neg and pos terminals of the battery once you have started the car. Then, put your A/C on and measure the voltage. (If the A/C being activated kills the engine, put on the headlights and your blower motor on high speed). Report back with your findings in both cases.
 

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1992 W124 260E
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Discussion Starter #9
Before you do any more part replacement, confirm that the alternator is working properly. You should measure 13.7 to 14.0 v DC across the neg and pos terminals of the battery once you have started the car. Then, put your A/C on and measure the voltage. (If the A/C being activated kills the engine, put on the headlights and your blower motor on high speed). Report back with your findings in both cases.
Engine off: 12.6V
Engine running: 13.99
Engine running +AC+lights: initial 13.68V
Then went slowly down 13.52 and possibly lower if I waited longer.
Engine off: 13.83V

Haven't done voltage drop test or X11 pin 2&3 yet.

Will drop and service alternator next. Suspect alternator/ brush of voltage regulator... maybe. Might as well do it while I'm at it... Lol
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Measure your duty cycle average voltage first. Nothing wrong with your alternator/regulator based on those numbers.

- Cheers
 

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Yes, those are good numbers. I would leave the alternator and regulator alone. Install a new 02 sensor if you want peace of mind since yours is very questionable, and as Dolucasi suggests, run the duty cycle test.
 

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1992 W124 260E
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Discussion Starter #12
Measure your duty cycle average voltage first. Nothing wrong with your alternator/regulator based on those numbers.

- Cheers
To do this duty cycle average voltage, one just needs to stick positive and negative into 2 -ve and 3 +ve and read the meter?
 

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1992 W124 260E
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Discussion Starter #13
Yes, those are good numbers. I would leave the alternator and regulator alone. Install a new 02 sensor if you want peace of mind since yours is very questionable, and as Dolucasi suggests, run the duty cycle test.
But why wasn't the car giving me any trouble for the last 1+ year even when the 02 sensor wasn't even hooked when I bought it? I only reconnected it this week.
I think I will install a new 02 sensor per your suggestion. I think the sensor is already 27 yrs old...

Tq

Sent from my JSN-L22 using Tapatalk
 

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I hear you but you need an O2 sensor in the loop for the car to run really as intended. They aren't expensive any more (generics on ebay). Have you ever had problems with the EHA (the little black device on the rear side of the fuel distributor)? This enriches the mixture and although the standard failure is a fuel smell and leak that you can't fix, there could also be an internal issue that can cause driveability issues. Chase the Duty Cycle as Dulocasi suggests. I'm just throwing out other food for thought. Another failure point is the seals the injectors sit in. They cause a vacuum leak when they fail.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,260 Posts
To do this duty cycle average voltage, one just needs to stick positive and negative into 2 -ve and 3 +ve and read the meter?
Yes. Also measure 2 -ve ad 6+ve and read the system voltage. These measurements have to be done with the O2 sensor hooked up otherwise it is moot.
You may have to turn on the diagnostic voltage. In CA cars there is a button to turn it on near the battery area.

The answer to your other question is that once you disconnect the O2 sensor, you loose feedback control and your AFM and FD turns into just a little more than a cheap carburetor.
So it will run crappy (not fuel efficient or emissions clean) but it will most likely not stall, etc unexpectedly

The life of the O2 sensor is about 100k miles on a new engine. A lot less for a worn engine that keeps covering it with soot.
So you will need a new O2 sensor as well..

- Cheers!
 

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1992 W124 260E
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Discussion Starter #16
I hear you but you need an O2 sensor in the loop for the car to run really as intended. They aren't expensive any more (generics on ebay). Have you ever had problems with the EHA (the little black device on the rear side of the fuel distributor)? This enriches the mixture and although the standard failure is a fuel smell and leak that you can't fix, there could also be an internal issue that can cause driveability issues. Chase the Duty Cycle as Dulocasi suggests. I'm just throwing out other food for thought. Another failure point is the seals the injectors sit in. They cause a vacuum leak when they fail.
They're expensive here, equivalent to $95 for a Bosch O2 sensor. If I were to buy it on ebay, the cost of transportation would be more than the price of the sensor, seriously. Local parts shops do not carry MB parts and if they do, I would need to order them. I mostly get my parts from a relatively cheaper shop in Kuala Lumpur which specialises in Mercedes or continental cars.

EHA? I now know where it is. Lol. FYI, this problem has occurred for the last 3 months.

I should be getting the O2 sensor tomorrow and will install it and run the duty cycle.

Until then....

Sent from my JSN-L22 using Tapatalk
 

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1992 W124 260E
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Discussion Starter #17
I hear you but you need an O2 sensor in the loop for the car to run really as intended. They aren't expensive any more (generics on ebay). Have you ever had problems with the EHA (the little black device on the rear side of the fuel distributor)? This enriches the mixture and although the standard failure is a fuel smell and leak that you can't fix, there could also be an internal issue that can cause driveability issues. Chase the Duty Cycle as Dulocasi suggests. I'm just throwing out other food for thought. Another failure point is the seals the injectors sit in. They cause a vacuum leak when they fail.
Can one do a test to id leaking at the injectors?

Sent from my JSN-L22 using Tapatalk
 

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1992 W124 260E
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Discussion Starter #18
Once I install the new O2 sensor, I'll do these two procedures.
1. duty cycle average voltage 2-ve & 3+ve
2. Followed by, system voltage 2-ve & 6+ve. Is this where one carry out lambda control adjustment?
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,260 Posts
Once I install the new O2 sensor, I'll do these two procedures.
1. duty cycle average voltage 2-ve & 3+ve
2. Followed by, system voltage 2-ve & 6+ve. Is this where one carry out lambda control adjustment?
Yes after this, you should think long and hard before you do an adjustment. You will have to first verify that all other emissions components are in working order before you make any adjustments, otherwise you are just tinkering around the edges.

Take the measurements and post them here, we are more than happy to assist you, And if the oxygen sensor is toast, you have to replace that first.

- Cheers!
 

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The forum used to tell us where members were by displaying the info with their avatar. Unfortunately progress has marched backward and we don't know that information without each member providing it. Silly. Anyway, yes, I understand that in KL you have challenges getting parts at a reasonable price.

As far as testing the injector seals, there are a couple of ways to do this. One is to use a smoke producing device to inject smoke into the intake system while the engine is off. The main objective is to flood the system with smoke and wherever smoke leaks out into the atmosphere, the location of the smoke is a potential vacuum leak. Another method is to use a propane torch (without the flame - just shooting propane out of the the torch head). SInce propane will have the tendency to increase the idle when it is introduced into the air fuel mixture, you can point the torch at suspected leak points while the engine is running and make note of which locations cause the idle to rise when you introduce the gas. For example, if you are pointing the nozzle directly at an injector seal (an inch away), and the idle increases only to decrease when you remove the nozzle/gas, then you have a good reason to change the injector seals.

Having said all this, your problem (stalling when you switch on the A/C) is an issue that injector seals alone will not cure. Does the A/C work when it is switched on and the engine is running?
 
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