Gutless from idle

[Pat]

I've always thought my 2009 VSK was a bit lacking in grunt at takeoff. If I don't warm it up on a cold morning it barely gets up my (admittedly steep) drive. I tried replacing the BCS a while ago but the replacement was a dud(!) and in the end I just adjusted my driving style and forgot about it.

Recently however the other half has started using it to tow a horse trailer and after watching her massacre the clutch on a hill start I thought I'd better see if anything was out of order.

I came across this post (https://www.nissan-navara.net/threads/d40-fuel-pressure-airflow-boost-readings.110821/) which shows small boost while sitting in neutral (once warmed up). Mine on the other hand doesn't show any boost until I get to about 1500rpm while sitting in neutral.

Just for clarity, if I'm driving and let it drop to say 1000rpm, its boosting fine throughout the rev range - the lack of power is just when you first go take off.

Also, to rule out other things - I've done a fair bit of routine and preventative maintenance already, e.g. replaced the vacuum hoses, cleaned the MAF, replaced the SCV, timing chains, etc. There's no smoke, no error codes, good compression, and good fuel pressure.

So - when should I start to see it go from negative (vacuum) to positive (boost) using the torque app? At a warm idle? Sitting in neutral at say 1300-1400 rpm? Only when driving?

Like I say it boosts fine throughout the rev range once moving. If everyone else sees boost at idle then I guess it's my BCS, but would like to be sure.

Thoughts? What else causes gutlessness at takeoff but good power elsewhere?

 

[Pat]

Example when in neutral at 1500rpm. Compare this to the link I posted earlier where the other guy had boost at idle.

 

[Old.Tony]

There shouldn't be much boost at idle. Mine has not had any boost at idle from factory until now, and I'm no longer using a BCS - I'm using a Tillix valve.

I did have a spreadsheet here with fuel, boost, throttle and speed (RPM and km/h) figures in it, calculating the amount of fuel consumed to take my Navara from 0 to 50km/h with engine RPM restricted to 2,000 and again at 2,500 then 3,000 rpm. I could have looked up some boost figures in there, but I can't find it. I don't recall my car producing a lot of boost at idle (mine idles at 750rpm give or take a few). It has to be over 1,000rpm to start getting any boost, but that's a little low to be taking off especially with a trailer. Boost should be coming on fairly strong when moving (in gear, vehicle not stationary) above 1,400rpm with full boost achievable at 1,600rpm and torque climbing steeply from 1,400rpm to 1,800rpm and levelling off to a peak somewhere around 3,000rpm.

The D40 is geared a little tall in first, and it's been suggested more than once that manuals are less appropriate for towing - although I admit I prefer a manual motorcycle and tow with it (I've got a pic somewhere ... ahh ok, found it, below). Up a hill the old girl struggles to get started (400kg of bike, 250kg of trailer - 1st is a little tall and it's only a 5-speed), but then so does my auto Navara with a 2.5T caravan behind it.

Important note: the ECU won't command a lot of boost in neutral. If your boost is suffering, you might have a problem with the Neutral Position Switch (NPS) in the gearbox. On the D22 it sits up high on the gearbox and is a blue plug from memory, but I haven't seen a D40 NPS. You could try unplugging it and see if that changes anything - your NPS may not function well when it's cool and this should identify it (and let you fix it).

If that doesn't work, could you graph Engine RPM + Intake Manifold Pressure, and I'll do the same in my car, which will behave differently because it's an auto with no ECU control of the turbo, but should show some things the same - I'm thinking along the lines of how fast the engine has to rev in order for the turbocharger to produce boost.

Oh, and two more possibilities - first, a faulty actuator on the turbocharger. Best seen on a dyno, but you should be able to see some significant movement of the rod beneath the actuator when someone revs the car from idle to 2,500rpm. Second - how are your brakes? The vacuum pump that provides the suction to manipulate the actuator also feeds the brake booster and we've had a couple of people report their boosters to be faulty. If your brakes are reluctant to bring the car to a stop, this could be your problem.

 

[Pat]

Thanks Tony, that's a comprehensive reply

600kg of bike & trailer wow! I rode/raced sports bikes for 30 odd years till my body told me enough was enough, and now just look enviously at guys on bikes... sigh...

I'm not going to have a chance to play with the Nav for a bit but will graph the RPM vs boost when I can. I'll also try unplugging the NPS if I can find it(!). Brakes are good btw, and the actuator seems OK too - jiggling at idle and moving freely when revd.

Guess I'm jumping to conclusions about it being turbo related, but I just cant think what else it'd be given there's no other obvious issues and it pulls well enough when on the move...?

Shame the manuals are so tall in first, might have to think about an auto if she keeps mistreating the clutch.

Thanks again, and will update soon.