I am looking for an explanation for why just replacing the spark plugs in my 1991 300SL 65k miles would correct an engine stumble at throttle tip in from a stop. This imtermittent stumble would only happen until the engine reached normal operatin temp.

The plugs that were removed after 10k miles look clean and to be the proper heat range. Every time this problem has occurred it was fixed by either replacing a cracked dist cap or changing plugs.

sldan

Did you remove Platinum plugs?

Scott P.

Scott P

This engine did not use Platinum plugs. I have always used the OEM plug.

sldan

A new dist cap can make a big difference. I have experienced this on other cars.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I am wondering what is it about the engine ignition control, fuel system control, etc that makes this engine so sensative to the condition of the spark plugs?

Just wondered if any of the senior techs out there have put any brain power to this issue!!

sldan

hows yer eng wire harness?
you should not need sp plugs that often.

george

Possibly the coil output .
With new plugs, the profile of the center electrode is sharp and square, which allows a quicker (Lower.) voltage/amp discharge across the gap.

As gas errosion rounds off the electrode profile, voltage requirements increase and a weak coil will need more time to build up a charge to spark the plug....which sometimes will be a non spark event...missfire...or even the turbulence in the chamber blowing out the weaker spark.

Another reason why multi-ground electrode plugs have come into use on late model engines so manufacturers can prove/provide no tune up during the DOT mandated emmision complience distance.

You'll find loads of interesting reading if you Google 'spark plug'.



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"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

dkveuro

I think you are on to smething. I had not thought of the coil but spark voltage and duration are a fnction of the coil's ability to provide the energy for a long hot spark.

The weak spark could cause a lack of engine response with a cold engine and a rich mixture. Initally the problem appeared to be a a classic lean mixture issue.

Thanks for the suggestion.

sldan

Does your vehicle have the 'G' coil design or the conventional type ?

I have found the 'G' type to fail more often than the conventional type.



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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

The coil does not look like what I would call a conventional coil.

The part number is F3000-35769.

I think I have attached a photo but not sure I did it correctly!

sldan

Conventional coils look like this..

http://www.sec-shop.com/parts_126/coil_1.jpg

I would recommend renewing the coil you have with another...used, from wrecker yard.
Local company here sells them ( Mercedes type.) for $50.00.



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__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

The coil must be what you are calling a G coil.

I will replace it.

Thanks,

sldan