1991 300d, 257k

The car doesn't have the proper amount of power to get up hills or to even accelerate from say 15 mph to 35 mph on a flat area. Before and after that, the car does ok.

Previously when this problem would come up every 7 years or so, the fix was to run Liqui Molly diesel purge to clean the injectors. I just did a diesel purge maybe a year ago and was surprised that I needed another one so soon, but this time doing another diesel purge hasn't really helped. It helped just a touch, but not much.

After testing the car for a day after assessing the effectiveness or lack thereof of the diesel purge, the next day I replaced the pre-filter and main fuel filter, and that hasn't helped either. I'm going to get some of that blue stuff you put in the fuel tank today, to clear out any potential algae in the tank filter but I highly doubt that's the problem.

Any other thoughts of anything I'm missing? I don't think the crossover tube is clogged with any gel; I checked that a year ago and it was as clean as a whistle.

I'm thinking maybe the injectors aren't popping at the right psi or aren't spraying well enough. Would doing a pop test on them and watching the spray pattern help? I had the injectors taken out and cleaned maybe just 4 years ago.