Everything needs to be right and then they’re acceptable. But anything that’s off, even just a little seems worse cause you don’t have much to work with in the first place. So, assuming the compressions good, the valves are right, then a diesel purge or a good shot of fuel additive is about it around town. For the road tire pressure makes a difference. Some of the additives don’t seem to make any difference – The “Red Line” stuff works best for me. Keep a clean air filter, but it’s really got to be nasty before that’s going to do much

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89 300E
79 240D
72 Westy
63 Bug sunroof
85 Jeep CJ7
86 Chevy 6.2l diesel PU

"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius