Navara loss of power can’t figure it out not boost solenoid

[The j man]

Hi i have a 2009 yd25 r51 210ks rebuilt engine
I had a problem with the boost solinoid after the rebuild I bought a cheap one and didn’t fix the problem I was still getting low boost I bought a Nissan one and it fixed it I’m getting 15psi normal and 20 at full.
car drove good for a while I was getting about 500 - 600ks to a tank but then it started struggling uphill and I am only getting around 400ks to a tank. It is like I have to drop the gear to get uphill and the car holds lower gears more And is slow at full. I have changed the filter cleaned the boost sensor cleaned the maf egr is blocked reset fuel pump changed boost lines injector cleaned through 2 tanks, I have a bit of black smoke but not allot. i checked the transmission fluid and it is pretty old and brown could it be that ? Anyone had this issue I can’t seem to find any other answers besides boost solenoid

 

[Old.Tony]

It's not just a boost solenoid, the vacuum hoses also play a part. If any of them have cracks, or turn easily on their connectors, they could easily let air in (reducing vacuum). There's a little under 3 metres of hose involved, it's all 3mm inside diameter and the last time I bought some (couple of years ago now) it was $5/m at Supercheap Auto.

The cheapest way to test the BCS is to take it completely out of the picture. Find the vacuum hose that comes across the top of the motor and connects to the BCS - remove it. Now connect this directly to the turbocharger actuator and take the car for a drive. The only issue you might have here is that if you're developing full boost, rapidly taking your foot off the throttle will cause an overboost in the intake and could pop a hose off (or burst it, or the intercooler). The trick is to accelerate nice and hard to see if the turbo's behaving, but gently come off the throttle so the turbo winds down gently. You'll hear it if you come off too quickly as a series of clatters as the intake hosing expands and returns to normal.

 

[GunMentalGrey]

Plus one for vacuum hoses, 2009 seems about the right age for gem to get a bit perished. Mine went and had similar symptoms. Replaced and back to full power.

 

[The j man]

I changed all the boost lines even the one on the boost sensor on the inter cooler with brand new lines and I’m getting full boost At the sensor

 

[Old.Tony]

EGR is about the only thing that's going to do that if you're getting full boost at the sensor, but yours is blocked so unless the blocking plate has failed, that can't be it.

Your gearbox might request a reduction in power because it's sensed something wrong internally, and changing the oil won't hurt especially if it's not a nice clean colour. I'm not sure this is it though - but you can't cause any problems by giving the gearbox fresh oil!

Your car should have had a DPF fitted (I have the exact same 2009 diesel auto) and this might be causing trouble. It usually shows other signs, like a DPF light or clouds of grey/white smoke (which stinks, it's unmistakeable). It won't give you grief while the engine is cold, but once it's warmed up - if it needs to do a regen - it should start pouring fuel into the exhaust stroke to heat up the DPF. If your DPF is intact it might be stuck in a loop where it's continuously trying to regenerate (burn off the soot inside the DPF). If it's unable to complete this (certain conditions are required for a DPF regen to be maintained) it will try again when the start conditions are met again.

Usually these conditions are:

* Engine operating load < 100%
* Engine RPM > 1600 (vehicle speed > 70km/h) (*note 1)
* Engine coolant temperature above 85C and below 105C

Note 1: I've had my DPF try to regen at 50km/h, because I was consistently running the engine at around 1800 rpm. I noticed this because at the time my DPF sensors were stuffed and my DPF was lacking some of the matrix internally (there may have been some surgery involved in this area with a cold chisel and a large hammer) so my car produced large clouds of grey/white smoke.