D40 Too much Turbo Vacuum

Hi Guys,
I bought a repairable write-off, 2007 D40 STX manual with 140,000 km on the clock. Perfect condition except for the dead motor. Injectors were out and some oil spray in the engine bay. No history available.

Long story extremely short, I did a dual chain mod, s/mass flywheel and HD clutch. Ran it and realised (the hard way) that the original problem was oil seal failure in the turbo. The engine began self-fuelling.

I have fitted an aftermarket turbo; it works ok, but the actuator is pulled on hard from start-up. Ive swapped the line to the old Garret turbo and same thing happens (full on except a slight pulsing) at idle. My guess is that the Garrett had failed because of overspooling.

I find plenty of comments about turbo control solenoids that don’t work, but never about one that works too well.

I have used a scope and measured the wave form to the solenoid and it appears to be correct. Before I rush out and buy a new solenoid I am wondering if anyone has had this problem, or is the vacuum pressure regulated back down the line.

Unfortunately, my manual shows the former YD25 vacuum air intake control system. This truck has electric control. Seems the vac system is quite different.

I haven’t measured the vacuum but it does not seem excessive. On the bench test, the solenoid opens and shuts correctly. The intercooler pressure sensor appears to be functioning, -in fact the only time I get the MIL on is when the sensor is disconnected.

Any thoughts or past experience will be appreciated. Signed, Bloody Frustrated!

Welcome to the forum!

First observation: the 2007 model YD25 had vacuum operated actuator as per that manual. Vacuum is provided by a pump on the right hand side of the motor near the oil filter via the solenoid that you've tested.

These turbos do spin rather quickly - they're supposed to make over 100,000rpm. They'll never do that at idle no matter the setting of the vanes, there's just not enough exhaust pressure. I have a spare turbo here that I should really pull apart to see which way the vanes go when the arm moves.

The waveform you've measured might be correct (100Hz) but the waveform will command a certain amount of open time vs closed time and that governs the amount of vacuum directed to the actuator. Brakes are obviously ok so it's not a fault with the vac system (brake booster is connected to THAT vacuum system). The open/closed cycle is governed by the ECU and that's going to be based on inputs from the crank angle sensor (mostly for rate), mass air flow sensor, turbo boost pressure sensor, neutral position switch, throttle position sensor ... vehicle speed does also come into play, as does coolant temperature, clutch switch - they're all connected to the amount of revs + boost that can be generated.

I would then think that only two possible things could make it over-produce boost (and really, we're not certain that this is the case yet - perhaps the "stationary" position for the vanes is fully open?) and those things are an error in the ECU (based on, perhaps and more likely, an error in the response from one of the aforementioned sensors) or the physical spring that returns the vanes to their position isn't strong enough (I have to assume that there's a spring there - I can look at my spare turbo tomorrow).

Have you taken it for a drive? How's the boost at light throttle application?

Thanks Tony,
I appreciate your input and will go back over the vehicle and re-assess, given the areas that you mention.
Yes have driven it briefly, bear in mind it is still unregistered until inspected due to the write-off status. Have used local streets and my long 3.5:1 driveway.
It was fairly unimpressive. Never driven a Navara before, so my bench mark is a newish 3.2 BT-50 and a diesel Hyundai i30, both of which rip up the hill in 2nd gear. The Navara made it in 1st gear.

As an experiment, I cut a slit in the hose to the actuator and it appeared to be a bit more lively.(wishful thinking maybe )
As said, both actuators on the old Garret and on the new turbo, pull full on at idle and stay there. I set up my bore scope to observe the new turbo’s action through gears, it stays full on.

I should probably mention why I am so cautious. When I first pulled the motor down, I found the fly wheel grinding into the bellhousing. All main bearing bolts stretched or broken. ‘We’ reached the conclusion that the Navara had been in water and Hydrolocked. However, there was no piston or rod damage.

I replaced the main bolts etc and went for a drive. It ran perfectly until I gunned the motor. She redlined for about 5 seconds before I managed to shut down. I disconnected the intercooler and drove home sounding like my old Fordson tractor. Stripped the motor and found the new main bearing cap bolts had gained an extra 5-10mm. Naturally investigated further and realised the turbo oil seal was shot.
As I said frustrated.

The 3.2L BT50 has lots of torque and is very impressive at low RPM, it's not a fair comparison!

Boost figures are the important ones. I'd imagine that at low RPM, without sufficient exhaust pressure to drive the turbine hard enough, the vanes would open fully to allow the most amount of exhaust to flow onto the turbine, but you should start to see that tapering off at about 1500-1600rpm as the exhaust flow reaches a level where the turbine can spin rather well. Which makes me think of something else you can try to see if it's working properly ...

If the turbocharger control system is working properly, it will allow a small amount of boost to allow the engine to rev but will close the vanes down when there's enough exhaust pressure to spin the turbine up properly. This means that revving the car (when stationary) to about 1800rpm (well and truly in the zone where the turbo will spin at high revs) should see the vanes close - and boost pressure should remain low. If it tries to climb high (when in neutral) part of the control system is faulty.

So looking at my old turbo (and moving the actuator) reveals that there's no external spring that I can see, it's either inside the actuator itself (likely) or in the vane mechanism (unlikely due to the heat in there). Here's a pic. I wonder if changing the actuator might help you?

Thanks Tony, I expected the BT50 would be a formidable opponent. Along with your comments, I will bone up on turbo function. Also strip the Garrett to help understand .
Will be in touch if I have a disaster or revelation.

Incidentally, talked to a few 4x4 specialists and engine reconditioners. None had heard of the crank blow out I experienced, save, mains damaged by broken crankshafts.
Cheers

Tony, thanks for your past advice, as a courtesy I thought I should conclude the discussion. I used an oscilloscope to check the wave form being sent to the vacuum. It was corrupted, probably due to a bad crank sensor.
The truck ran ok on the road, but, given my experience, and add the D40's extensive bad rap online, I just could not trust it.
So I took it to the dump.