VGT Percentage 50% Off?

[David Hurley]

I have a 2007.5 3500 6.7L complete delete new batteries.

Everything seems normal when I turn the truck on; the VGT percentage goes to 34, then to 85, and stays.

I have a city diesel actuator on the factory turbo.

After it starts, the VGT actual is always exactly 50% over desired, so if the desired is 40, it will be at 90, never more than 1% away from 50% off.

The strange thing is that I can unplug the actuator after it has started and then plug it back into the truck.

It kind of sneezes, LOL.

Basically, it cycles the actuator, and then it works fine, exhaust brake and all.

Also, the actual vs. desired matches after the unplugged reconnect fiasco.

I’m running an MM3 tuned by DRD, and the actuator just went out of warranty in February, so I’d like to avoid having to buy another.

Any help would also be greatly appreciated.

That would be great if someone could tell me the normal oscilloscope readings for the actuator.

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[AK Bob]

Strange actuator behavior: I would contact City Diesel directly to see if they have seen this before or have any suggestions.

I'm unsure what you mean by normal oscilloscope readings for the actuator.

Other than verifying a good power and ground, you can only see the CAN bus activity.

Decoding the CAN message for any given vane position for comparison would be difficult and inconclusive.

As you stated, the actuator works correctly after you cycle it, so your PCM sends the correct information over CAN.

I believe the problem is in the actuator electronics at startup.

Please keep us posted on any suggestions or information from City Diesel.

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[David Hurley]

I contacted City Diesel, and they had no interest in dealing with it.

Regarding the oscilloscope readings, I meant that if I used my breakout leads, I would be wondering what the correct voltage readings on the leads for the can bus should be.

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[AK Bob]

I contacted City Diesel, and they had no interest in dealing with it.

Regarding the oscilloscope readings, I meant that if I used my breakout leads, I would be wondering what the correct voltage readings on the leads for the can bus should be.

When back-probing between the two J1939 CAN pins at the actuator connector with a multimeter meter you should read an average voltage of approximately 0.5V DC. CAN High to ground 2.7V DC and CAN Low to ground 2.2V DC when there is communication.

The best way to measure and see the CAN message is with a scope.

See the attached CAN waveform message.

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[David Hurley]

When back-probing between the two J1939 CAN pins at the actuator connector with a multimeter meter you should read an average voltage of approximately 0.5V DC. CAN High to ground 2.7V DC and CAN Low to ground 2.2V DC when there is communication.

The best way to measure and see the CAN message is with a scope.

See the attached CAN waveform message.

Thank you so much.

I have an oscilloscope, and the breakout leads. I need to log it while I drive with the actuator still working.

I'm just reading as well.

I’ll log it on Friday or Saturday and post the scope graphs.

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