Help Help Help Please..

[smoothcoupe]

My W140 500 Coupe Is Performing Really Badly.. Ie Wont Accelerate Any Better Than My Wifes Ford Fiesta On Initial Take Off... The Responsiveness Just Seems To Be Gone... On Full Throttle It Wont Red Line It Gets To 3500 Rmpm And Just Bogs Down...... Items That Have Been Replaced Are As Follows...

1. Air Mass Sensor
2. Both Fuel Pumps.

Is There Any Thing Else To Check Ie Leads, Plugs, Coils, Sensors Etc.......... Any Help Would Be Appreciated......

 

[BaldGuy]

Private message guydewdney... he is our resident coupe expert.....

 

[frog1520]

Is There Any Thing Else To Check Ie Leads, Plugs, Coils, Sensors Etc.......... Any Help Would Be Appreciated......

My W140 was misfiring which caused a major loss of performance. In my case it was a knackered lead. I think if you can get it on the computer, it tells you if theres a misfire and on which cylinders which should hopefully narrow it down...

Good Luck!

 

[shrekky]

Really need to get the error codes that are occuring,because i know that alot of mercedes have a "limp you home mode" for certain things that go wrong.and the sysmptoms are like what you describe.its designed to stop the driver over stressing the engine,ie the early rev limiter,rough idle.

 

[guydewdney]

where are you based? I have a basic diagnostic computer plug in I can try to find out whats bothering it...

these things are so complex that guessing the fault is almost pointless.. but check for split hoses / loose connectors.

what year is it? if pre-96 (i.e. do you have side air bags / parking sensors not little aerials and body coloured bottom halves - all of this is post 96) then also check the dreaded wiring harness

see:-
http://forums.mbworld.org/forums/forumdisplay.php?forumid=29

and
http://www.mbnz.org/forums/forums/forum-view.asp?fid=13

and do a search for wiring harness.

also:-
http://pages.prodigy.net/jforgione/MB_S500.html

or here for wiring diagrams:-
http://www.autolib.diakom.ru:8001/CAR/Mercedes-Benz/1997/S500/SYSTEM WIRING DIAGRAMS/

 

[hitt]

Just a thought.
The exhaust was the culprit for similar symtoms in my case. The CAT got blocked up when a pre-cat filter failed and disintegrated, I couldn't get past 3000rpm.
Just do a check to make sure the pressure coming from the exhaust seems normal (assuming you have some idea of how it was prior to your problem).

 

[jgevers]

Hi,

What are the symptoms. If the engine is missfiring I would check caps, rotor arms, leads and plugs. If it is just lack of power I would do a back pressure check in front of the cats (rattle test might suffice) and check fuel pressure. The pumps might be ok but the pressure regulatorn on the rail might be faulty.

regards,

Job