300ce engine loses power at highway speeds

Sir: I have a 1988 300CE with 108k miles. Recently, while driving at highway speeds, 60+ mph, the engine seems to lose power and the red "check engine" light blinks on for a few seconds. It feels like I am losing power in one or two cylinders for 5 to 10 seconds. Then, the power resumes, the engine light goes out and everything is OK. This problem will only occur about once in 20 or 30 minutes of highway driving. I took it to my local mechanic, he drove the car and, of course, this problem did not occur. Any suggestions? Thank you, tjw tward@hseinc.biz

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Body and Interior Specific Aid

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Questions and Answers

Chassis Model Number

W124

Challenging diagnosis

Hi TJW, That is going to be a tough problem to diagnose. Unless it happens on a more regular basis you will not be able to diagnose it by checking the fault codes or putting it on an engine analyser. From your description I would first suspect an electronic ignition problem. I once had a customer bring in a 1989 300E that would sporatically just quite while driving. It got so his wife would not drive it because she was so scared it would just quit running at a stop light. Of course it would start right up again and every time he took it into a shop it would not do it! I explained that we would have to start replacing parts - starting with the least expensive first and then working on to a few more expensive components - I told him that there would be no guarantees but I would try to help. After checking his maintenance records I learned that it had been a very long time since any regular maintenance items had been replaced. After pulling the spark plugs I noticed they were badly worn and showed signs of oil fouling. I changed the spark plugs and ask him to drive it for a few days. He called a week later to say the problem was fixed and never came back.

If it has been a while since you have done regular maintenance like plugs, wires, cap, rotor, fuel filter, Ov relay, etc I would recommend you read my 103 Engine Tuning Guide and perform the maintenance as outlined in that manual. CLICK HERE to read more.