Hey Guys!

I have been stumped with my 1996 E320. She now has 114,000 miles and is driving funny. I get a hunting idle, poor gas mileage, and rpm surges irratically. I have replaced the MAF and checked all wiring and throttle body. All good. I have been advised that the O2 sensor needs to be replaced. There is not CEL on the dash or "Check Engine Electronics" message. I went to look for the O2 sensor and i noticed that there are 2 listed. One that plugs Pre-Cat and one for the Cat Converter itself. Has anyone changed their O2 sensors on an M104 before? Any suggestions would be appreciated! Overall, this old girl is doing great!!!!!

Mike

__________________
My Work:
Mercedes-Benz Manhattan, Inc.
Business Development
536 West 41st Street
New York, NY 10036

-My Garage-
1996 E320: White 118,000 miles ~Dad's Driver~
1996 E320: Green 109,000 miles ~Mom's Driver~
~My Babies~
2000 SL500: Desert Sand 96,000 miles
-Previoulsy Judge Judy's-
2008 E350 4MATIC Sport
-Flint Grey/ Ash/ Black Birds Eye Maple-

That car has only 2 O2 sensors.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Good morning DOC,

I read in one of the MB manuals, that one of these O2 sensors can cause considerable issues such as engine shuts off and won’t re-start due to the O2 sensor harness grounding with the drive shaft. Do you happen to know if this is correct? My O2 sensor's harnesses look fine with no damage.

The reason I ask is that my 1996 E320 which I though I had repaired wont start, the vehicle is been sitting on my driveway for the last 10 days. At first the car will die as I was driving it, and I would need to wait at least 2 hours so it would start again. So I proceeded to replace the CPS, but I continued to have the same issue and it got worse after several days . So I replaced the MAF and Cam Sensor without any positive results.

Currently the car will only start after sitting for 24hrs and it will only run for 3 seconds and shuts off. Once the car shuts-off the car will crank but won't start again until the next day. By the way when it starts for the 3 seconds it seems to run great. I really need someone experience to help me troubleshoot this issue; I would appreciate any help that can be provided. The following parts were changed within the last 30 days:

Crank positioning sensor
Camshaft sensor
MAF
knock sensor (2)
Transmition wire harness
engine Cooling sensor.

I would appreciate any guidance an help. Thanks in advance.
Norman

Sounds like fuel delivery - fuel pump or fuel pump relay.

Have you checked if the fuel pump(s?) are running while cranking?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I have to agree. That sounds like TYPICAL fuel delivery issues. I am goign to say it is either the fuel pump relay or Fuel Pressure Sendor Regulator. Do a search on both, you will find TONS of info...

The M104 is bullet-proof! But it's all the Barbed Wire around it that causes the problems!

-Mike

__________________
My Work:
Mercedes-Benz Manhattan, Inc.
Business Development
536 West 41st Street
New York, NY 10036

-My Garage-
1996 E320: White 118,000 miles ~Dad's Driver~
1996 E320: Green 109,000 miles ~Mom's Driver~
~My Babies~
2000 SL500: Desert Sand 96,000 miles
-Previoulsy Judge Judy's-
2008 E350 4MATIC Sport
-Flint Grey/ Ash/ Black Birds Eye Maple-

With few exceptions, O2 sensor issues generally appear when the system enters closed loop. If problems are exhibited immediately at startup, it's not likely that the O2 sensor is the culprit.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Well,

I do appreciate everyone's response. The pump seems to be working, but it is one of the last items that I have not replaced, and it is the original one (11 years old) It maybe an intermittent issue, and that is why at first I was able to start the vehicle but gradually it got worse . The relays I did check and are working as they should (I had a spare K40 module and try it just to make sure that relays were not the cause of the problem). I will be picking up a new fuel pump and filter early this afternoon and I will try to install it late in the afternoon. I hope this solves the mystery. I forgot to mention on my prior e-mail that I also had changed the fuel regulator located on the fuel rail.

I will post my findings after replacing the pump. Hopefully this will take care of the problem. I appreciate all the suggestions

Well, I'm out of ideas. I replaced the fuel pump and filter yesterday afternoon, and did not fix the culprit. Anyone has any recommendations what to test or what part should I be troubleshooting?

Once again the following parts are new and where replaced:

Fuel pump
Fuel filter
Fuel pressure regulator
Crank Positioning sensor
Cam positioning sensor
MAF sensor
Cooling sensor
Knock sensors
Tried using another K40 module (relays).

Thanks in advance.

Norman