I have an older diesel SUV (a Toyota Hilux surf 1996). When I step more on the pedal for power it spews a lot of black smoke. When I do it gentler, it spews less. Besides not being heavy on the pedal, how do I reduce the black smoke? I also load with Techron Diesel fuel and I do clean my exhaust pipe at least once a week. Assuming I am limited in budget (as in I cannot buy a new car), how do I lessen the black smoke? TIA.