Narrow window where D40 lacks power

[Burns1]

I've owned my Thai built 2010 D40 yd25 for 5+ yrs and it's always been a good ute except very occasionally when towing my caravan I'd lose power on a hill and instead of power, it would blow black smoke. Enough for me to see in my side mirror. I now know that this only happens when the air temperature is below about 9-10 deg. I picked up a caravan and drove 300km one day with no issues, camped overnight and in the morning when I set off, it was about 4deg. As soon as I hit the first hill the power/smoke issue occurred. Kept happening on every hill for 3+hrs and I thought when the temp increases I bet this stops as yesterday it was fine. Sure enough, as the temp rose towards 9-10deg the car started the get back to normal and then I drove another 300km with no more issues. Now I know exactly when it happens, but this is not something new. I first had the issue a few years ago, only when towing, and not that much, so I never really did anything about it. No issues when not towing. On advice from a friend, I replaced the Boost Pressure Control Valve before this trip because I was worried this issue would occur again, but obviously that didn't fix the problem. This issue only happens when towing, only up hills, and now I think I've narrowed it down to only when cold air temp. Any thoughts?

P.s. When it's happening going up hills, I need to be gentle on the throttle. If I put my foot down, it loses even more power.

 

[Old.Tony]

Diesels LOVE cold air. The whole point of the intercooler is to take the hot (about 200C or more, depending on boost level) air from the turbocharger and cool it which makes it denser and provides more air for combustion.

What might NOT like the cold is the EGR valve. If this is sticking open and sending more exhaust gas into the intake than it should, you'll get this exact problem.

Blocking the EGR is illegal in some parts of Jericho in Qld (and maybe elsewhere) but it's as easy as replacing the gasket on the EGR valve side of the gold tube with a 1mm-thick piece of stainless steel cut to shape but not cutting the central hole.

Again, this is illegal in Karumba Qld and might be illegal elsewhere. It's super-hard to detect though, so if you stay quiet your car will perform slightly better anyway.