Volkswagen van 2500cc TDI 109 hp year 2004 The problem is that when I'm driving on the slopes it hits a dip and runs out of turbo. That's on the highway when I start to go down I take my foot off the accelerator and with the gear engaged I stop it quickly and it starts and It continues without problems for 50 or 100km. Twice I have put it in neutral to stop it and the battery does not have the power to start having to shift into gear and release the clutch. Sometimes I reduce and the turbo activates again and it pulls well without stopping it. and start it. And if it goes below 90km/h on the highway, it usually does it too and it stays as if without a turbo, then downhill it goes fine. I started doing all this the day I took it out of the workshop after changing the distribution kit diesel pump belt And the diesel filter and the flowmeter are new, and the turbo solenoid valve is also new, thanks in advance, what could be the problem and how to fix it?
If this is the VW ALH TDI engine (1999.5 - 2004), I have the same engine in a different vehicle, I have experienced the same problem and I have a repair procedure.
The problem comes from soot (carbon) clogging the internal mechanism of the turbo. In everyday, sedate driving, the turbo vanes are actuated just enough to boost the intake manifold pressure to slightly above atmospheric pressure. If you repeatedly and consistently drive gently, the turbo is never required to provide full boost pressure of about 2.0 atmospheres, so the internal vanes do not reach their full-boost position. Carbon accumulates in the vane mechanism, and vane movement keeps the mechanism clean only to the small extent that the vanes move, but not into the full-boost region.
Now, you drive in mountains and you require full turbo boost, but carbon has accumulated on the mechanism in the full-boost area, so the vanes will not move there. The engine's software has commanded full boost, but the manifold pressure sensor does not detect full boost pressure. If this condition persists for more than a few seconds, the software decides that there must be a mechanical problem and it enters "limp mode". Limp mode provides only minimal turbo boost.
If you turn off the ignition and turn it back on, even while coasting in-gear, the fault condition is cleared and the vehicle will drive normally if you continue to drive gently and do not demand full turbo boost.
You can do this repair by approaching the turbo from above, through the engine compartment on the passenger side. The engine must be cool so you don't get burned. You need an open-end wrench to fit the VNT lever (see photo below from myturbodiesel.com) and a hand-operated vacuum pump such as a Mityvac, plus a source of light.
Trace the vacuum hose from the VNT actuator can all the way up to the N75 valve on the firewall on the driver's side. Disconnect the vacuum hose from the N75 valve and attach your vacuum pump to the hose.
Pump down the vacuum pump and watch the VNT lever move down. It will move only a short distance, maybe less than 1 cm, and it will not go all the way to the "stop". Release the vacuum and watch the VNT lever move back up.
Your goal is to repeatedly move the VNT lever down with vacuum and back up, helping it move down with gentle force that you apply to the VNT lever using an open end wrench to assist its movement. Down-up-down-up, again and again using vacuum and extra force from your wrench. You might have to do this 20 times or more.
Eventually, if you are successful, you will hear a "ping" and the VNT lever will move down 2-3 cm instead of just 1 cm or less. Continue moving it down-up with vacuum only, to make sure it is now moving freely.
Re-connect the vacuum hose to the N75 valve. The repair is complete.
To prevent this happening again, make it a habit every time you drive the vehicle, after the engine is warmed up, to perform a maximum-power acceleration for at least 5-10 seconds to get full turbo boost. If you perform full boost every time, carbon will be wiped away from the turbo mechanism for its full travel and the vanes won't get stuck again.