2004 XC70 - Sluggish when compared to another 04 XC70?

[NullenVoyd]

Hello MVS! Wondering if any of you awesome people have some thoughts on this issue.

Recently picked up a 2nd 2004 XC70 intended as a parts car, which ended up being in better shape than my 1st one, and had local indie voov shop work on getting it nominal. Among a few minor issues, the biggest problem with the new one was a lack of power, felt like the turbo wasn't engaging at all.

Shop found turbo itself in pretty good shape (from what they tell me), but TCV wasn't responding at all. They replaced and were able to get some boost, but still found it lacking. They checked the intake/boost pressure sensor and that seemed ok. Checked the timing and noticed it was a tooth off (I'm not sure which direction), and pulled the belt and re-aligned it. At that point they were satisfied with how it ran.

I get it back and, while every other aspect of the car is much improved especially over my 1st XC70, the power just doesn't feel there as much as in the 1st one. I don't hear the turbo at all on the new car, but maybe the old car's turbo is louder than usual? I don't feel any boost when driving new car, but maybe old car was tuned (no clue, no way to find out?).

So I got into VIDA and tried to get some graphs from a couple loops around the block next to the shop. Not sure if these are the best sensors to look at for this kind of issue, but I figured it would be a decent starting point.
First graph is the new car. Looks like it's boosting but doesn't feel even remotely as 'ready' as the old car. Putting throttle under load gives me a throaty 'gurgle' like it has fuel but wants more air. Like when I'd floor it in my 91 2.2L non-turbo Accord wagon.


Second graph from roughly the same trip in the old car. OMG, feels so much better! Power is RIGHT THERE, turbo is audible and you can hear it spinning up and down pretty responsively. Even instant pedal down doesn't gurgle at all, just adjusts and launches, which is sometimes scarey in a nearly 2 tonne hunk of metal.


Boost pressure looks similar enough. Old voov waste gate seems to be activating much more. Idle (numeric readings in lower-right by colour key) MAF reading seems pretty different, like old car thoroughput is much higher? Shop thinks its something with the turbo, I wonder if its more in the timing, loosely possible old car was tuned, but judging by how previous owner treated and 'repaired' the old voov, I highly doubt that.
Thoughts/ideas? Really appreciate any input here, and let me know if there's more info I can provide to give better insight.

Edit: FWIW no codes reported.

[abscate]

The cBV diaphragms get old with age and can develop holes, that will inhibit boost. It’s a dissasemblyto diagnose , though. Not an easy job on turbo XC due to access. I think VIDA says remove turbo.

[oragex]

Also the MAF sensors get covered with small dust particles. This reduces their performance. However, just cleaning with the MAF spray doesn't really change much. I managed to clean mine with a small brush and there was a good difference on how the engine felt - mine is the non turbo MAF so much easier to clean. I personally think an MAF should be replaced every 80K or so even if there's no code - just my theory. Problem is, is rather expensive. One possible way is to buy new one online (Fcp, etc) test and return if there's no change

[abscate]

Also the MAF sensors get covered with small dust particles. This reduces their performance. However, just cleaning with the MAF spray doesn't really change much. I managed to clean mine with a small brush and there was a good difference on how the engine felt - mine is the non turbo MAF so much easier to clean. I personally think an MAF should be replaced every 80K or so even if there's no code - just my theory. Problem is, is rather expensive. One possible way is to buy new one online (Fcp, etc) test and return if there's no change

I think MAFs are one of the most over-replaced parts in the business. MAF codes come from many ills, and vacuum leaks top the list. It’s much easier to follow the

Code...part...replace... mantra

......Than look for vacuum leaks, but the holed hose is much more likely.

[NullenVoyd]

The cBV diaphragms get old with age and can develop holes, that will inhibit boost. It’s a dissasemblyto diagnose , though. Not an easy job on turbo XC due to access. I think VIDA says remove turbo.

If CBV is leaking, would I see/feel anything on the vacuum line coming off of it?

Also, can someone clear something up for me (I've not worked on boosted cars much before).
Bypass valve activates in order to push more exhaust across the turbine, or to reduce turbine activation? Graph makes me think valve at rest lets bypass occur, but it closes (activates) to force more across turbine and thus spin compressor up, generating more boost. If there is more bypass valve activation on the old car, seems like ECU is asking it to boost more?

Can I manually (temporarily for testing) force full turbine engagement to see if that improves power?

Thank you both for the responses!

[vtl]

If CBV is leaking, would I see/feel anything on the vacuum line coming off of it?

Yes. Disconnect the hose from the TCV side and do the mouth vacuum test CBV is a royal PITA to remove on the car, but still doable (I did that a month ago).

Also, can someone clear something up for me (I've not worked on boosted cars much before).
Bypass valve activates in order to push more exhaust across the turbine, or to reduce turbine activation?

Wastegate diverts exhaust from turbine wheel, CBV releases fresh air from the intake piping.

Graph makes me think valve at rest lets bypass occur, but it closes (activates) to force more across turbine and thus spin compressor up, generating more boost.

Make sure wastegate is properly tuned: the flap should start moving at 12.5 kPa of vacuum.

Can I manually (temporarily for testing) force full turbine engagement to see if that improves power?

Stock 14T turbine is beefy enough to cause a permanent engine damage if overboost happens and not counter-acted immediately by ECU.

Unless you have a DTC set that relates to a reduced engine power, most likely the problem is in turbo's vacuum control. Check wastegate, CBV, TCV hoses, vacuum leaks in intake.

Turbo itself can be seized, too. Not that uncommon.

[NullenVoyd]

Wastegate diverts exhaust from turbine wheel, CBV releases fresh air from the intake piping.

Gotcha. On this car, when I see "Turbo control valve duty cycle" raise to something above 0%, is that opening or closing the wastegate (I'm assuming closing, to build up pressure)?

If I'm seeing that behavior in the graphs on the new car, is it safe to think that the turbo is working, just not as effectively, or the ECM isn't being as aggressive with applying boost?

Turbo itself can be seized, too. Not that uncommon.

Which is what the shop and I were kinda assuming from the beginning, but they swear it's spinning.

Should I be able to easily hear the turbo on these cars? Old XC70 sounds like a subtle vacuum cleaner. New XC70 I swear I can't hear it at all. But if it wasn't working to the point I can't hear it or feel it, shouldn't I get some kind of DTC?

Really appreciate your input on this, and apologies for all the questions, but if I can build a decent understanding of the underlying rules and operation of a thing, it makes it so much better (and meaningful) to troubleshoot.

[vtl]

Gotcha. On this car, when I see "Turbo control valve duty cycle" raise to something above 0%, is that opening or closing the wastegate (I'm assuming closing, to build up pressure)?

Open to divert gases.

If I'm seeing that behavior in the graphs on the new car, is it safe to think that the turbo is working, just not as effectively, or the ECM isn't being as aggressive with applying boost?

Yes. Maybe not ECM itself, just the control circuit is not working.

Should I be able to easily hear the turbo on these cars? Old XC70 sounds like a subtle vacuum cleaner. New XC70 I swear I can't hear it at all. But if it wasn't working to the point I can't hear it or feel it, shouldn't I get some kind of DTC?

No, they are almost silent in the cabin. Some engine grunt - yes, turbo noise - barely.

[NullenVoyd]

So the vac lines around the turbo (as best I can do a quick check without tearing anything apart) seemed pretty good.

But look what I found when poking around the other vac lines (attempted to attach picture from phone)!

Vac lines around intake.

This is plugging into the middle top of the intake manifold, and then to the junctions and elbows to go wherever else. But that's essentially a hole in my pressurized intake, right? Is that part of the PCV system?

Do I need to give my shop a spanking and not bring them any more homemade cookies?

[matthew1]

Where do those three lines go?