Spark knock on 97 E-420

[Greaves]

I have not ever owned a M-B before, so I don't know what to expect regarding performance, maintance, etc. When I bought the car it had 54,000 miles on it. It has 62,000 now. Recently, it begain spark knocking on light acceleration, or hard acceleration. Spark Knock is particularly heavy on pulling a significant hill. I use 93 Octane Exxon or Amoco gasoline. The car was given the full 60,000 mile service when I bought it. This included new spark plugs, and all fluids flushed, etc. It did not spark knock then. Any ideas on the source of the problem, and potential solutions?

Thanks!

[Tom Hanson]

You very likely need a new knock sensor. MB # 003-153-44-28 and I can get it to you for $165.00 plus shipping. It's down on the left side of the engine. Fairly big harness looking thing.

[Greaves]

Mr. Hanson, thanks for your suggestion of a possible defective knock sensor. I will bring this to the attention of my M-B dealer service dept. tomorrow when I visit them for service. The car is a Starmark Warranty car, so if the knock sensor is defective, it will be replaced. Since I made the original posting of the concern, I have discovered that brands of gasoline do have an effect on the problem. Exxon and Citgo are the worst offenders, and Crown 93 octane premium seems to do more to minimize the problem. However, it does not cure the problem. We will see if there is any mechanical issue tomorrow. Thanks again for your information!

[Greaves]

I have just returned from my M-B Dealer Service Dept who worked on the spark knock issue. The bottom line is that they reccommended Techron Concentrate to clean up the fuel delivery system, and clean out the carbon build up on the valves, and upper end of the engine combustion chambers. This information is consistent with other threads on this forum discussing the merits of Techron. We will see how it works in my car for this particular problem.

Cliff Greaves
North Carolina