Fluctuating boost

[Stevod40]

Hi all I have an 07 d40 auto turbo deisel. I just installed a saas boost gauge following post on this site. Helped a lot but now when I drive the boost fluctuates between 15-20 mark not constant. I have owned turbo commodores but not a turbo deisel before. Is this normal?

 

[Old.Tony]

It sure is. The Navara runs a "variable vane" turbocharger which makes it easy for the ECU to adjust boost levels. As fuel input (even for constant load&throttle) is constantly varied, and in normal driving the load is often changing, the ECU is constantly adjusting everything including the turbocharger output.

That doesn't mean that nothing's wrong - your car's 8 years old this year. The turbocharger might need new journal bearings, the vac hoses could be diminishing, the vac solenoid may be ok but I'd check the electrical connections to it. The actuator itself has a diaphragm that can perish over time, and there's a diaphragm in the brake booster that may also cause problems.

If your boost is coming on nicely from about 1500rpm and peaking around 3000rpm-3500rpm then I'd suggest that everything is going fairly smoothly at the moment. Try a nice long hill and see how the boost performs when the car climbs hard, if the variation is within 2-3psi of average (which it sounds like it is now) then I wouldn't be too concerned.

 

[Stevod40]

Ok thanks it's sounds like it's ok then. I was worried because I just spent a bit on it by replacing turbo and both timing chains.