My 93 Mercedes 500SEL has the low power problem in cold or hot engine, the exhaust smell like gas, idle is very rough, very slow in uphill situation.

I changed the following parts:
1. All new plugs.
2. All new plug wires.
3. New Rotors and Caps.
4. New air filter.

After changed all the tune up parts, the car still has the same problem.
Changed the fuel filter, problem disappear, and I thought the problem was fixed. Good power and very smooth, okay for about 1.5 months(1500 miles),
passed the smog test .

Now, the car has the same problem, very low power, rough idle, very bad smell from the exhaust. Changed the fuel filter again, still has the same low power problem. Please advice and help. Thank you!

You could have some dirt in your gas tank....

A compression test would also be a good idea.

Karsten

Get an auto stethoscope or use the end of long screw driver to listen to the fuel injectors.. You should hear a crisp clicking nose from each injector. If not, you either have a failed or clogged fuel injector causing your power loss.

If all the injectors checkout okay, check the fuel pressure on the fuel rail.

__________________
Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML

The fuel system and the fuel pressure was checked okay ( in an auto shop).
They informed me that the fuel is clear and with good pressure.

From what I read in this forum, the problem may be the OXYGEN SENSOR.
Do you know the location of the oxygen sensor on the 500sel, it has one or 2 sensor? Thanks again for your help.

If your S Class is like mine (with the M119 engine) your oxygen will be located on the exhaust manifold, top side of exhaust, under the car before the cat. I only have one on my exhaust.

Did you mechanic read the codes from your engine? Depending on the mileage of your 93 500SEL, it might be time to change your O2 sensor. A poor performing O2 sensor can cost you $$ on gas milage.

If you decide to replace the O2 sensor, you'll need a 24mm box type socket for your s500. When I removed and replace the O2 sensor, the O2 sendor was a little tight, but after a few taps on the wrench with a hammer, it broke the seal and came out without difficult.

Attached Thumbnails

   

__________________
Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML

Thanks for the information.
I do not know what model engine on my 500SEL, I know it has a V8 5.0L engine.
My car has 200K miles on it. I will replace the O2 sensor.