XC90 T6 -- Low boost? Hjelp!

Swaybars · Post by **Swaybars** » 08 Nov 2021, 11:10

Hey everyone -- I haven't been able to get much help with this elsewhere, so I thought I'd ask!

I think I might be experiencing lower boost than expected on my T6.

No codes for it, but I dropped back to the stock tune to check.

Most I saw in VIDA stock logging was about 4PSI doing 2nd gear pulls onto the freeway. According to IPD, stock boost on this car is 8 PSI. Weird thing is that it was showing TCV duty cycle around 50%, does that mean the ECM was trying to bleed boost?

Then I went back to the tune I was running, I noticed I barely gained 1PSI. Seriously -- at times TCV was at 100%, but boost was totally flat.

Now 4 PSI is right around stock wastegate pressure. Is there any way to see if this might be a TCV issue, a wastegate issue...where do I start? What even is the working boost on these? 8 PSI honestly is higher than I've ever seen in VIDA.

Swaybars · Post by **Swaybars** » 10 Nov 2021, 11:16

Bumpity bump

now trying to determine if I also have a cracked intercooler, or it the hose is just leaking. Tightened it down and cleaned around it but the end tank was totally covered in oily gunk.

Post by **matthew1** » 10 Nov 2021, 11:48

Did you look for a crack? When my 850's intercooler blew a) it was loud and b) the crack was easy to spot. But it was on the bottom so it was right in my face when I had it up on ramps.

Swaybars · Post by **Swaybars** » 10 Nov 2021, 12:05

matthew1 wrote: ↑10 Nov 2021, 11:48 Did you look for a crack? When my 850's intercooler blew a) it was loud and b) the crack was easy to spot. But it was on the bottom so it was right in my face when I had it up on ramps.

I did look once I got the thing cleaned up a bit. There was so much greasy gunk that I couldn't even see the plastic itself! I have no idea where exactly it is leaking from because of how completely gunked it is. I'd guess it was coming from the hose, but I mean...just look at how everything is completely covered, even things up and out of the way.

I took the hose off and re-seated it. I've heard of small fractures occurring in the hose flange. I'm having trouble getting more than ~5 PSI out of my car according to VIDA, so at this point I'm looking for anything weird.

Post by **matthew1** » 10 Nov 2021, 12:17

Is your fuel economy suffering?

Swaybars · Post by **Swaybars** » 10 Nov 2021, 13:22

Hah...my mileage was suffering from the first moment I started to daily an XC90

Jokes aside, it is basically what I would expect. Where things get weird is that this car is running a tune targeting 300+ HP, so at wide open throttle in 1st or 2nd (3-4th mean I'm going 100+ MPH so no use doing pulls with them) the ECM seems to be asking for more boost -- TCV literally pegged at 100% duty cycle if my foot is on the floor in 2nd. I am NOT an expert but from my understanding, if the TCV is at 100%, that means it is "closed" and the turbos are basically allowed to make whatever pressure they can.

But I'm making like 5-6 PSI, maybe a spike to 7. According to IPD (best source I could find), boost pressure of the B6294T stock is 8PSI!

Post by **matthew1** » 10 Nov 2021, 13:30

I'd lose the tune while you figure this out. It's just adding a variable to a lengthy variable list already.

Do you have a friend with a T6 you can swap in known good parts like TCV?

That intercooler looks difficult to feel around on, but I'd do my best to get at it and do just that. No gloves. You want to find a crack.

Eliminate variables until it's the source only one remaining.

Oh, and check all vacuum hoses and components they connect to... then do it three more times.

Post by **matthew1** » 10 Nov 2021, 13:31

And to be clear: you never knew of the "before" situation? It has always been the case of low boost while you've owned it?

When my 850 blew the intercooler (Ok ok, it was its driver who did it), MPG went from a dismal 17 city to 14 or so...

Post by **RickHaleParker** » 10 Nov 2021, 14:32

matthew1 wrote: ↑10 Nov 2021, 13:30 That intercooler looks difficult to feel around on, but I'd do my best to get at it and do just that. No gloves. You want to find a crack

Pump smoke into the fresh air intake pipe and smoke test the whole system.

Swaybars · Post by **Swaybars** » 10 Nov 2021, 15:38

matthew1 wrote: ↑10 Nov 2021, 13:30 I'd lose the tune while you figure this out. It's just adding a variable to a lengthy variable list already.

Do you have a friend with a T6 you can swap in known good parts like TCV?

That intercooler looks difficult to feel around on....

Sadly there are so few living "old style" T6 cars around these days...I wish I had a friend with one! Out of 70+ cars at the IPD meet, I was the only one!

Intercooler is indeed SUPER hard to get at. Yesterday I had to pull the headlight and vacuum booster pump to get to the hose clamp, had to pry it off from below. No obvious cracks that I saw or felt, so I'm assuming it was the hose clamp?

I just ordered a TCV, I had a credit with eEuroparts so it was only $30 shipped. Can throw it on my XC70 if I don't need it (that car has a TCV code). My XC90 does have 150K miles and is ~18 years old, so I could see it being TCV related.

No CBV on these later T6 cars apparently!

I did test the TCV -- fired up VIDA, activated it. It clicked and buzzed, so it does respond. Could it be failing to hold up to higher pressures? ~ 5 PSI is basically wastegate pressure.

Rick, what is the best way to smoke test? Should I just take it to a shop for that?