I have a 1987 w124 with a m603 which I had new Monark injector nozzle tips installed. The car ran great for a day and then some symptoms started occuring. The car would bog down right before the turbo kicks in so probably from 1600 to 2100 rpm the engine would really bog down and lag. When the turbo kicks in, it feels great though. I bled the injectors of air by loosening all 6 of them with the engine off and cranking the engine. It got much better, but still not great. Then I changed the fuel filter, I actually dumped the old filter fuel in a plastic container and it came out black. The car ran much better. Then the turbo stopped working, at the same time, the transmission shifts very hard, like the vacuum modulator stopped working. I bypassed the turbo limiter and the car went like a v8 for a couple of days. when I floored it for the first few times after the bypass, it spit out thick black smoke and then huge power kicks in. Drove like that for a couple days, and it started bogging again. Any ideas out there? Vacuum issue? Fuel delivery? Air in system? all of the above?

 

I'll check out the fuel tank filter. Thanks.

 

If something is growing in the Fuel Tank you will need to kill the "infection". Startron is one Product and Bilbor (spelling?) is another.

Startron claims to have an enzyme that breaks up the dead Bodies small enough to pass through the Filters and that can mean less changes of Filters until the problem has worked its way out of your Fuel System.

Even if you remove the Fuel Tank and have it cleaned or otherwise clean the Tank you should treat the Fuel with something as the infection is still in the Fuel Lines.

The Local Auto Part chain Stores may or may not have it. Stores that have Truck Parts and especially Boating Stores are more likely to have it.