D40 will not boost until 2200 - 2500 revs

[jack.haran]

Have a problem with my Navara whereby I get no appreciable boost below 2200 revs. I had to replace the turbo as the shaft broke on the input side and noticed while doing some diagnostics on turbo failure that the pressure feed from the intercooler to the MAP was disconnected.
Things I've tried to get boost at circa 1400 revs are, replaced boost control solenoid, replaced MAP sensor and checked for vaccum leeks. (I'm going to put a vaccum gauge on the pipe to the turbo actuator in the next day or so).
Using a diagnostic tool, I can get about 18psi boost and fuel pressure looks good as well.

I notice the the linkage on the actuator doesn't flutter on idle, this may be an indicator to someone here.
Also, (probably unrelated but in case this has been seen by others) my temp gauge jumps between cold and actual temperature until such time as engine heats up and holds well thereafter. I'm going to replace it this evening. Any pointers would be appreciated.

 

[Old.Tony]

A vacuum leak would be my first guess too, since you've replaced the BCS. Keep an eye out for hoses that move easily on their connector as well as cracks etc.

I wouldn't worry too much about the actuator arm movement at idle, some cars do it some don't, I don't know why there's a difference, but I do know that cars that are behaving normally don't always have a moving actuator at idle.

The jumping temp gauge is a concern, but points to a bad electrical connection more than a faulty sensor. Now just where this fault is might be a tough one - obviously start with the sensor itself. Look at the wires coming off it - try flexing them and see if they feel normal. I once checked a Nav and discovered that while the insulation of a wire was good, the wire within was broken and you could tell by the odd angle the insulation made at that point.

 

[jack.haran]

First video is of the vac input to the turbo actuator, as you can see it's all over the place. Not shown here, but I measured the input to the BCS at a solid 25 inches but there was also a reading of 20 inches from the BCS to the air intake. So I reckoned I had only about 5 inches on the actuator if I averaged the pulsating gauge over time.
Without getting out the scope, I believed I had some sort of noise / interference on the CAN bus so I went straight to the temp sensor connector. The fan started the second I touched the connector, so I cut the wires as close as possible, removed a kinked section and soldered them back on. I then got three T pieces and connected 3 x vac gauges. In second video bottom gauge is from vac pump, middle is form air intake and top from actuator.

 

[Old.Tony]

At idle that's not too bad. You can rev the thing a little but in neutral the ECU won't command full boost so it might still be jumpy as the ECU holds back the boost (there's no need to spool up dramatically when you're not in gear and moving).

Good show on the temp sensor. Broken wires - especially those that are still in their insulation - are real buggers to find.

If you stick an oscilloscope on the BCS you'll discover that the thing cycles at 100 hz, and it opens for some of those cycles. It's a little like a modern electronic speed controller for an RC car or boat, where for 10% open, out of 100 cycles it will open for 10 of those cycles distributed across that 100 cycle group (meaning every 10th cycle it will open). This will appear erratic but on the actuator end - being a device that can't react in 1/100th of a second - the arm moves more slowly. We still see some cars (mine included) that have actuator arms that jiggle at idle and they're working perfectly.