Cm870 VGT issue

[Rawze]

Here are some observations while he was here ...

He has a very old style of actuator system. All it consists of is a pwm (pulse width modulated / analog valve control signal) output from the ECM with zero feedback for position or pressure of any kind. It is unlike a lot of CM870's out there, and is an early version.

Something is wonky with it for sure. Even when we manually sent 0 - 60 psi air pressure to it with an external regulator connected right to the actuator piston, it did not move smoothly, but rather jerky. It would hang, then jump by 30-40% at a time or more as the pressure was changed slowly, indicating that perhaps the control arm was too stiff.

The PWM signal looked noisy due to the large coils of the actuator control on the o-scope, but it changed consistently whatever you commanded the thing to anywhere from 0% to 100%. The output pressure was form 0 psi to 120 psi at 100% consistently as well. - We tried 2 different actuators and control valves with the same results.

I monitored all the data in the ECU and it is commanding the turbo exactly as it is directed to without any derate, etc. - When it asks for 20-35% or so, all seems well and it somewhat moves close to these positions. Above this though, it start asking for 40% or 50%, and the air pressure matches this, but the thing jumps all the way closed instead of moving smoothly. when it asks for 40% or so, engine sees boost pressure low, demands more from the turbo, but by the time the arm overcomes the stiffness, it is already demanding max closing and it over-boosts/spikes like mad, chuffs, then has to back it off again. - I.E.> Wonky as all hell until it settles out.

- Something is very wrong with it somewhere. I have never messed with a CM870 myself, so I have no reference on how the turbo arm is supposed to move when applying air to it manually. Nor do I know how stiff it should feel when moving it by hand. I also don't know what typical pressure should result in what position.

-- He has apparently had this problem for a while, and that explains why he has blown out several exhaust manifold gaskets, etc. over this. I measured more than 90+ psi in the exhaust manifold when it would spike. It is also a very likely cause of why his CAC blew apart a couple times in the past.

While he was here, we pressurized his engine and found/fixed fixed the CAC, stopped a massive boost leak between his air compressor into his crank case, replaced all the exhaust manifold gaskets and polished it all up so it would hold. He also had YTS replace the guts of his turbo, but how stiff the control arm was when he got it back is in question at this point. It feels like the wiper ring (anti-carbon buildup ring) he used is perhaps too tight?. Maybe even if it is supposed to have one installed on that model at all?.

it could also be the ECM, or perhaps both?