Over the last month, I have twice had the same type of problem with my 400 SE from 1992.
Both events have happened after 5-10 kilometers of driving.
Weather conditions were rainy/wet.
The last event:
After approx 5 kilometers, I had to slow down (almost stop) due to road works.
When accelerating away from the stop, the car almost died on me, with some very erratic engine revs.
I managed, just, to keep the car moving, and got approx 800 meters further, when I had to stop for a red light.
After a few seconds, the idling got very erratic, and the car finally died on me.
I tried to get it started again 4-5 times, but it would not start. I turned on the emergency warning lights, and got out, to place the warning-triangle on the road – this I was able to do, when the 40-50 cars behind me had managed to get by me (I was stopped in a traffic light, during rush hour
. I called for help, and was towed away some 30 minutes later.
Observation: After the warning lights had been on for these 30 minutes approx. some of the lights on the car stopped blinking, acting very much as if there were insufficient power to light them up.
Question 1: The battery in the car – at the time – was an 3-4 year old 83 ah Exide (taken from my W126). Should such a battery not have the power to sustain warning lights for more than 30 minutes ?
Today I tried some experiments on the car:
- - I charged and installed an apparently newer (was in the car when I bought it 2 months ago) 63 ah battery in the car. The output I measured at 12,something V.
- - I started the car, and let it idle for 10 minutes.
- - No problems, smooth idling.
- - After a couple of more minutes, the idling started to become erratic (just like at the road works)
- - It continued like this, but did not die.
- - I tried to “stress” the electrical system by pressing the window-up buttons, to close the already closed windows. What I noticed each time I did this, was that the cabin lights dimmed noticeably each time (both the light in the instrument cluster, as well as the lights in the ceiling, which were on). I wouldn’t think this should happen, or am I wrong ??
- - While stressing the system, I at the same time, pressed the speeder pedal, getting the engine up to 3000 rpm. This had a positive effect on the light level.
- - After 5 minutes more, the idling became even more erratic, and I turned off the car.
I have searched a lot around the forum, and found that many other W140 owners have experienced similar problems to mine, and there seem to be a list of often-suggested things to try out, as far as I can see:
- Ignition coils
- Viring harness
- Distributor caps / rotors
- Oxygen sensor
- Mass flow sensor
- Clogged cat. Converter
- Starter lockout switch
- Fuel filter
- Intake Air Leak
Question 2: Can the batteri(es) be the culprits ? What sort of trouble can a worn out / too small battery cause ?
Question 3: What battery should I have in the car – any recommendations would be much appreciated ?
Question 4: If not the battery, which items on the list, would you suggest that I start with ??
Thanks in advance, for any help offered.