Have you changed the strainer In the tank? Checked the injectors spray pattern?


Now I hate that everyone immediately jumps to this, but it would be worth compression testing your 3.5 to make sure its worth continuing. If you've got a bunch if dead cylinders no amount of tuning will fix that.

Like joe said W140s are big girls, and they are rated at as near as makes no difference the same power as the 87 300D. I had a 1991 350SDL and my 1987 300D was considerably faster. And my 350 was in great running condition and compression tested well when I bought it.