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Car Forum / Mercedes-Benz Cars / December 2004help with an 87 420 sel
Here is my problem: I live in a city that requires auto emission tests annually. I took my car in to have the test done and it failed miserably. The hydro carbon count was 5 times the allowable limit. I was told that fuel is not burning as it goes through the engine. The car has been idling rough and getting poor mileage. My efficiency gauge lives at 3/4 to 1/2 what it should if running properly. Does anyone have any idea as to what the problem could be? O2 sensor(the light has not come on)? Bad plugs? thanks for any help you all can throw my way. aaron It defintely could be the O2 sensor and the need for new plugs and wires. P. > Here is my problem: > [quoted text clipped - 10 lines] > > aaron Sounds like multiple problems... First check all spark plugs for the condition of the electrode... what color is it? Rusty white? Seconds of all, your fuel mixture is too rich... this can be adjusted by the fuel mixture screw but I wouldn't play with this unless I eliminate other possible causes... such as spark plug wires (check for resistance about 1350 max ohm)... clean distributor cap and rotors contacts... inspect for any damage, if so, replace them both. Other possible reason is bad O2 sensor... what is the mileage? When is the last time you changed one? Well I have had the car for 4 years and i have not replaced the O2 sensor. three years ago the engine was rebuilt after my timing chain broke. I do not know if the O2 sensor was replaced. The distributor cap was firing away nicely and did not look dirty. I have not checked the cables other than a look over. > Sounds like multiple problems... > [quoted text clipped - 9 lines] > Other possible reason is bad O2 sensor... what is the mileage? When is the > last time you changed one? > Seconds of all, your fuel mixture is too rich... this can be adjusted by > the fuel mixture screw but I wouldn't play with this unless I eliminate > other possible causes Why not? Isn't it possible that this is the only problem and it's just seriously off? It'd be free and easy to check (3mm allen, stick it down in the hole in the air filter top, engage in bolt, push down against resistance of a spring, turn counterclockwise). Richard >> Seconds of all, your fuel mixture is too rich... this can be adjusted >> by the fuel mixture screw but I wouldn't play with this unless I [quoted text clipped - 5 lines] > resistance of a spring, turn counterclockwise). > Richard It's stupid to play with the mixture before verifying that the ignition system is functioning properly... You might cover up a problem, but you won't fix it. After verifying the ignition system is working right, then using proper gas analyzer or shade tree methods, the mixture can be adjusted. |
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