Here is situation. 1979 300SD W116, if I drive 60mph or more I abruptly lose power where I can barely maintain 50-55mph. this occurs about ever 10-15 minutes. if I pull over and let car idle a minute or three I can pull away with full power for another 10-15 minutes. Like there is a fuel restriction. But main filter has 8,000 miles on it, just replaced the prefilter because it looked dark. Turns out it was dirty outside clean inside. I did a shock of BioBor a week ago, no change, zero debriss making it to pre filter.

Tomorrow I will drive without cap on tank to prove its not a tank vent issue.

Any ideas. I though if it was algea I would get debris at prefilter. Car runs wonderful outside of this.

This started abruptly a week ago and I see no signs of an air leak.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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