Cm870 VGT issue

[Chamberpains]

This must be the "high mount" control module. Thats an early simpler version. I haven't worked with any of those yet. If it was a "Low Mount" Control Module I'd be very leary of it operating correctly. I had mine a few years back that was all over the place and very intermittent with sending the wrong pressures to the actuator. Random low boost and 3rd stage jake being very weak or spiking violently. They are not well designed and can throw pressures all over the place at random. I've worked with 2 guys that bought brand new Holset modules and still had a bad one right out of the box but they are far better than any reman or Ebay garbage. But that doesn't seem to be where your problem is. It all sounds like it's in the actuator. I'd call Cummins directly (not a Cummins Authorized Dealership) and see if they have some differences in actuators between the earlier models.

Also, this may sound simple but I've used a drop of oil in my actuator to ensure it moves smoothly. Obviously these systems are a bit clunky compared to an electric controlled system so I believe they need all the help they can get to operate smoothly.

You've eliminated this as a possibility, but, I recently had an actuator that would only leak at 40% - 65%ish commanded. So you couldn't just simply run the actuator open close test to find this sucker leaking. I had to pull the dog box and drive it to hear the air pissing out in those commanded percentages. I didn't have an adjustable pressure regulator at the time to run it thru the complete operating pressure. I do now though.

Also I don't know if this helps, but thru watching mine, I've noticed that while driving, the commanded percentage generally stays within 3 different values. 30, 55, and 70% mine generally only falls a few percentage point either way off those 3 values during operation.

Quote: 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.

This is why I tell everyone with these systems that any little kink, pinch, minute leak, in line obstruction (do not use teflon tape at any of the connections to avoid in line obstructions) any problem at all with them and they over boost or get really erratic boost pressures. You have to go over all the piping with a fine tooth comb and ensure that it has absolute unrestricted commanded air pressure.

Rawze, if you happened to record the ECM commanded percentage with its correlating control module signal voltage and then finally what the final actuator control arm measured movement is, and posting that, it would be a HUGE help to any one diagnosing or narrowing down problems with this circuit.