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.
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400 SE, 1992 (W140)
260 SE, 1986 (W126)
Typical alternator output should be about 14 volts while the engine is running. A fully charged battery should be about 12.6 V to 12.8 V. It would seem unusual that you are not getting any fault indication about your alternator if it's not working properly.
Examining the engine compartment more closely today, on my search for the MAF, I discovered something wrong.
The air filter box, on top of the engine, was not sitting tight on the engine !!
I suspect that this may have caused air to enter into the engine directly, bypassing the filters, and the air sensor located in one of big air hoses, sitting before the right air filter.
Q1: Can this explain my problems ?
Additional questions:
Q2: The cylinder holding the MAF (see picture “MAF cylinder dirty”), is very dirty at the bottom. Is this normal ?
Q3: The air filters are not that dirty, but from 2001. Problem ?
Reason for filter box being loose: the 2 vertical arms supposed to click into the 2 horizontal ones, at the back of the filter box are missing from the engine block – apparently broken off. (See picture “Air filter box”)
Q4: Would anyone happen to know how long these are ? I’ll try to fasten 2 screws instead, which can hold the filter box in place.
Today performed the following work to fix the problem:
- Generator output checked, and verified.
- New air filters.
- Cleaned the throttle with throttle cleaner spray (the dirty stuff is almost gone).
- Cleaned the MAF with air sensor cleaner spray (looks less dirty now).
Problem not solved.
Remains to be done/tried:
- New 100 ah battery (I am picking one up later today)
- Ignition coils
- Viring harness
- Distributor caps / rotors
- Oxygen sensor
- Mass flow sensor (replace)
- Clogged cat. Converter
- Starter lockout switch
- Fuel filter
- Intake Air Leak
i suggested a new battery to avoid the car not starting in the very near future, not becuase of your shutting off problem
here are the things to do IN ORDER until you find the problem, so you dont end up replacing the ENGINE trying to find the problem with no luck
-Spark Plugs (replace)
-ingnition rotor (clean with sanding paper/replace)
-dis cap (clean with sanding paper/replace)
-check wiring harness
-check ignition wire set for leaking spark
-replace fuel filter
-check fuel pump pressure
-check fuel injector(s)
vacuum leaks usually do not cause the car to die, unless they are major major ones, in such case, you can usually hear the vaccum leak before you can feel it, so i doubt thats what's causing it.
test the car after EACH components has been replaced/checked so you can find out for sure what caused it. do ONE thing at a time.
Since last posting, have performed the following work to fix the problem:
- Installed a new 100 ah Exide ultra extreme battery (Instead of the 63 ah).
- Replaced 7 out of 8 sparkplugs (Beru Ultra-X). Had some challenges getting the cap off almost all the plugs. Had big problems getting the cap off the last one (see picture). In general it appeared that the age and state of the ignition cables were questionable. There seemed to be 2 different types of cable (see picture) and some of them were very rigid, the rest soft and flexible. The red ones bore the MB emblem and sparepart id, the black ones did not. I cleaned the 7 caps with contact cleaner, before applying them to the spark plugs again.
Status: I have been unable to reproduce the problem today . However the weather is less moist today, than it has been the other days where problem have been apparent. Also I did not have a lot of time to play around, reproducing.
Will look for new ignition wires, to be on the safe side, and also because I will probably ruin the last cap, in my attempts at getting the last plug out....
lovely, replace your wire set, and check the ignition dis cap and rotor.
a long needle nose will help in these cases, have a new wire set handy before you start woking, the wires look like they are worn enough to snap if you force them out.
. I called for help, and was towed away some 30 minutes later.
(see picture). In general it appeared that the age and state of the ignition cables were questionable. There seemed to be 2 different types of cable (see picture) and some of them were very rigid, the rest soft and flexible. The red ones bore the MB emblem and sparepart id, the black ones did not. I cleaned the 7 caps with contact cleaner, before applying them to the spark plugs again.
. However the weather is less moist today, than it has been the other days where problem have been apparent. Also I did not have a lot of time to play around, reproducing.
Linear Mode
