Negative Boost (Vacuum)

[Black_Outlaw]

Ah yes. I have replaced my BCS as it was fluctuating between BOOST and NONE. My car was in a constant state of surge as boost came on, then off, then on, then off.

Not sure how that related to the negative boost on yours, or mine, though. The BCS was definitely not touched this time on my D40.

 

[Old.Tony]

Mine was acting a little more oddly. Under light loading it performed flawlessly with boost varying as demand changed. Under moderate to heavy loads the boost went to max and the ECU shut the thing down (forced limp mode).

What really sucks is that I'm not 100% convinced that it's actually fixed. I pulled out to overtake someone yesterday and as I accelerated, so did they. Harder acceleration was met with a surge-normal-surge-limp-surge-normal-urge-limp kind of power pattern. As I'd not had my new windscreen in long enough I couldn't monitor boost/fuel pressure/airflow etc. The car still picked up, but it did not do it smoothly like it used to. Subsequent attempts at high throttle/high load saw flawless performance.

I will say that my fuel economy has dramatically improved. I'm very tempted to whack the caravan on the back this weekend and find a big hill just so I can see how she behaves under max load - but I think I'll just be patient.

 

[Black_Outlaw]

Tony, longshot here, but I've also had the "surge, normal, surge" issue seperately and it was the SCV playing up and irregularly controlling rail pressure.

Im not sure if you've ever replaced yours? Removed and cleaned?

I tend to go for the "obvious" problems before paying out for the unknown.

With my cold-start issue, i knew that when the new SCV did not fix it, my gut told me it was needing pump seal kit / replacement pump. My logs from then and now prove it.

 

[Old.Tony]

My SCV is next on the list if things start playing up again. Have had no issues since so keeping my fingers crossed.

 

[big zetor]

my 2012 2.5 d40 does this aswell, goes from 20 odd psi to -13 every now and then, mostly in between gear changes from 5th to 6th and a few day's ago it went into limp mode whilst going up a hill in 5th and i wasn't really pushing it just cruising.

 

[jld40]

Disclaimer - not an expert by any stretch - but the torque readings show negative boost on mine from about 3-4k rpm; but the 2014 nav runs pulls fine and evenly throughout so I'm having a but of trouble interpreting.

It (somewhat variably) puts out a small amount of cont black smoke under heavy load which per Old Tony in another thread isn't than all that abnormal for this truck; definitely not clouds as per above. Its got 230k and hasn't had new injectors which I've been told may be contributing.

Here's the torque graph 3rd gear foot to the floor (all warmed up etc) - while the MAP scale is off its boosts at 22-23 PSI from about 2k rpm, drops off (when torque reports neg boost) and then goes back up around 4k. Part of me wonders if this is just an Aliasing sensor?

Has anyone figured this one out as yet?