D40 YD25 DDTI Turbo Adjustments On the car

[Kzin]

After a rebuild of my engine, an aborted Core change for my Turbo, & Chasing many Red Herrings, the truck was still not running correctly.

Using The Torque App, I noticed that When Accelerating hard on a flat road, there was only ~12-14psi of boost (see graph) and looking in at the turbo over the wheel, the actuator was not touching the stop screw at idle. The settings on the actuator have been messed with.

So In order to get the Boost back to stock, I have Adjusted(shortened) the Actuator Approx 2 turns. now the truck is running better, and I'm seeing up to ~17.8psi

I guess my question now is what is my target boost PSI, and is it possible that I could see someone else's Graph/Raw data of the same information?

 

[Old.Tony]

The YD25 in the D40 (with the GT2056V turbocharger) should develop around 18-20psi of boost. It can handle up to about 21-22psi standard but will start tripping the overboost warning in the ECU from 23psi onwards (this has been my experience).

 

[Scott52]

My turbo actuator had been played with by a previous owner. I had the same problem with about 14psi max. and it wasn't hitting the adjusting screw.

After doing the research I found the way to adjust the rod on a Garret Turbo is an iterative process with a vacuum pump with gauge and then a drive with the boost gauge. The actuator should be just touching the adjustable stop with 18in.Hg applied to the diaphragm on the top.

It takes several goes to get it feeling about right. If it's hitting the stop at 18 in.Hg but the rod is too short the boost comes on quickly and will overboost. So you lengthen the rod a bit and reset the stop position with the vacuum pump. So keep going in ever decreasing circles until it boosts to about 18 psi-20psi but doesn't come on strong too quickly and trigger the ECU over boost rules.

I bought a cheap 8mm open end spanner from Bunnings and ground the shank near the open end to get enough movement to loosen the stopper. I used a long ball ended hex key to turn the screw because the approach is from an angle.

It worked for me with max boost about 20/21psi with an occasional trigger of the ECU.

 

[Scott52]

Further to the process above I've done some more work on this problem as it seems we're often confronted with a turbo that's been fiddled with in that both the stop screw and actuator length have been changed.

This process laid out below seems to have worked well for me on my YD25 in the Thai 2011 D40. It's a good way to get a starting baseline if you're not sure what's been adjusted before. You need a vacuum pump with gauge, an 8mm ring spanner modified as described above and a long ball ended 2.5mm hex key.

Remove the three 10mm bolts securing the turbo heat shield and push it towards the firewall.

Loosen the lock nut, back out the stop screw so the lever arm can't touch it and use the vacuum pump to lift the actuator rod as far as it will go. This closes the variable vanes.

With the vanes still closed wind down the stop screw until it touches the lever arm then wind down another full turn and temporarily tighten the lock nut and mark the screw with a paint pen for a reference. I found this bit of information on a non English speaking forum. If I can find it again I will post a link. This initial setting and reference ensures the vanes never fully close which can damage a VNT turbo.

Adjust the rod length until it just touches the stop screw at 18 in.Hg. Use a thin strip of paper as a ‘feeler gauge” so you know when it contacts.

Road test with a boost gauge or Torquepro connected and you'll probably be moderately over boosting. This means boost will climb quickly and keep going until the ECU steps in and the boost will suddenly drop.

Loosen the lock nut and turn the screw down another ¼ turn down and road test again. In my case it was still over boosting but not as much.

I adjusted the stop screw a further ¼ turn down and road tested again. This time it would get to 18 to 20 psi and hold that pressure. Before the ECU would suddenly step in to cut it.

Individual YD25's may need the screw turned down a bit more or a bit less.

I checked the actuator rod again and it was still hitting the stop at 18 in.Hg or a smidge lower. IDparts (see video from 3:44) say 15 to 18 in.Hg is acceptable with 18 in.Hg being on the "safe side". Considering the accuracy of the gauge and the method of setting there's a bit of leeway with the rod length. As long as the lever hits the stop screw at around 18 in.Hg or a bit less it works. Remember the boost control solenoid is modulating the vacuum to the actuator in a closed loop to keep the boost within target settings so that rod is jumping up and down all over the place.

So I have the stop screw 1.5 turns down from when it first touched the lever arm with the vanes fully closed and the lever hitting stop screw at 17 to 18 in.Hg. It's running well.

Video from IDparts on how to adjust the rod length on a Garrett VNT turbo. Watch from 3:44