Something doesn't sound right, you don't adjust the tensioner on these cars, they are self adjusting. What did he replace on the tensioner? The little shock? The spring? The arm? The bearing?

Secondly what are the symptoms, it just failed to start? Even without glow plugs it should still start, just with more cranking.

If the glow plugs died suddenly, then check the strip fuse. Its in the black box behind the drivers side headlight, they often fail. Actualy over the winter its not a bad idea to carry a spare.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200