2006 ISX CM870 High Pyro, surging under load

[Rawze]

Is your replacement turbo an OEM certified reman or origional? -- or repaired/re-manufactured by some shop?

CM870 air actuated turbos can be tricky to install properly sometimes. Some have a floating ring (can turn freely and self-align) in the exhaust housing for the vanes to move in and out of, and some have a fixed ring (fixed shroud plate). if the one you just got has a fixed ring in the exhaust housing then it will hang, jump and not operate smoothly if the turbo was not installed onto the truck exactly right.

I.E.>Fixed ring (non-floating shroud plate) turbos cannot just be installed onto the truck without some adjustments and testing.

The older style were fixed ring, and it is also well known by turbo shops that reman holset VG's that even with the floating ring style, as they age, the ring seizes up permanently and cannot be freed up again even after cleanig, etc. and a rebuild ... Turning it into a fixed ring style. - Does not hurt a thing as long as the installer is made aware of this fact so that the extra alignments can be made on the truck during the install.

Turbos with a fixed fixed ring require the person installing it to remove the actuator (the air actuator in your case) from the control arm after mounting the turbo to the exhaust manifold and feel the control arms in/out movement by hand. The v-band clamp needs to be loosened on the exhaust side of the turbo a slight bit so that someone can clock the main body of the turbo one direction and the other a bit (a very fine adjustment amount usually) while the vg vanes are fully extended into the exhaust ring and find the centre point where they do not rub. - It does not take much mis-alignment at all for the whole thing to operate wonky if the vanes are rubbing against the fixed ring as they go in and out. On these types of turbos someone needs to always do this after mounting it to the exhaust manifold on the truck. This is because it is very common for this alignment to be slightly out of adjustment once the turbo is put in place.



Moving the arm in and out and adjusting the center housing to the exhaust housing alignment for the smoothest, least resistance is quite important, especially on CM870 because the ecm has no feedback for the vg movement and it has no idea if it has actually moved to the correct position or not.

- I would start there. Once that has been done correctly, you can also check the movement of the turbo air actuator by making an adapter and supplying air from a regulator and see if the actuator movement is fairly smooth and consistent from 0 to ~30 psi (maybe 0 - 60 psi, i forget) both before it is installed onto the turbo and after.

Tags:

air operated turbo, cm870 turbo, turbo problems, turbo hanging, turbo wonky, turbo issues, cm870 boost problems