Strange smell/odor after changing spark plugs


Asked by Feb 28, 2012 at 02:10 PM about the 1991 Mercedes-Benz SL-Class 300SL

Question type: Maintenance & Repair

After changing the spark plugs in my 300SL I am getting this strong odor while inside the car, really strong when idling. No lights come up in dash, runs great but after driving I end up with a bad headache from this smell. Anyone know what this could be.


5 Answers


It is possible that you have fitted the wrong spark plugs, check that the part numbers match the old ones or those recommended in your handbook. Spark plugs do have different heat ranges which can effect how the fuel mixture is burnt, this in turn will effect how much the Cat is heated and performs. Alternatively does the car appear to miss-fire or be lumpy at idle, if so you may have a faulty coil or lead or even a faulty new spark plug.

3 people found this helpful.

Hi Paul,. Thank you for responding. Well as my luck would have it the spark plugs i needed to have replaced was in German and and the numbers on them didn't match up with any plugs here in the U.S. I will double check and make sure the correct ones were installed. Those plugs were extremely difficult to remove. And about (Lumpy at idle), just today while heading out it did a quick bumpy/shake thing then stopped. II just need to find a great mechanic that won't take advantage. I HATE dealing with these guys.


Is it possible you have got the spark plug leads mixed up, it is easy to do especially if the plastic channel they are routed in has come off, check the leads they are usually numbered, if not the distributor cap is numbered BUT the numbers lie underneath the black cover!! Mercedes-Benz dealers are notoriously obnoxious buggers even over here in the U.K!! You may have more luck with a Specialist independant garage.

1 people found this helpful.

it may also be possible that you moved a hose loose or disconnected a vacuum line, these cars a have hoses and vacuum lines all over the place.


Thanks Guys, I wanted to let you know that the changing of the spark plugs did the trick. No more smell or choppy ride. My car really needs a tune up. I'm waiting for the manual I ordered. It's just too much for me to find a mechanic and take my car in. Too much meaning not knowing who's honest and going through the pick up lines....EVERY SINGLE TIME!

1 people found this helpful.

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