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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #1 ·
Hey everyone, I have fixed my low boost condition but I'm back again with another odd issue.

Realized that on occasion when I punch the gas at low speeds ~20-35 MPH (for the sake of the 4T65 I try not to do that often) I get some odd behavior.

After the rev-match/downshift to 1st it pulls HARD for a second or two. Then it feels and sounds as though throttle input, boost, or load has been cut. I don't know which. Then a second later it comes back with full fury and pulls hard up to ~6000 RPM. Overall it feels like a "hill" (lots of power) then a "valley" (very little power) and then a "hill."

With my limited knowledge I feel like it could be:
1. Boost control issues
2. Transmission slip
3. Throttle/drive-by-wire problems

If it were any other car, I'd keep doing WOT kickdowns for testing. But considering we're making ~320 HP now and the poor little 4T65 is doing its level best to hang on, stabbing the gas a bunch should be kept to a minimum.

Has anyone seen behavior like this with their turbo Volvo? Doesn't have to be an XC90, just trying to figure out where I should look first.
 

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I know nothing about your setup, but the behavior sounds a lot like a car I had back in the late '70s where the wastegate would stick, and the over boost protection would shut things down until it dropped back to a sensible level,then it would come back in again.
 

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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #3 ·
Hey John, thanks for the response! Aside from the twin turbos, the way boost is controlled on the T6 is basically the same as all turbo Volvos from the era, so if you have experience with those you'll understand the system on the T6. Same turbo control valve as the 5cyl cars. I replaced that a few months ago when I was having issues with low boost. Since then this has been an occasional issue.

Apparently, the ECU is supposed to "learn" the new TCV. I figure after a few months and over 1000mi that ought to have happened.

Any way to troubleshoot a sticking wastegate? One of them is real hard to reach.
 

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Hey everyone, I have fixed my low boost condition but I'm back again with another odd issue.

Realized that on occasion when I punch the gas at low speeds ~20-35 MPH (for the sake of the 4T65 I try not to do that often) I get some odd behavior.

After the rev-match/downshift to 1st it pulls HARD for a second or two. Then it feels and sounds as though throttle input, boost, or load has been cut. I don't know which. Then a second later it comes back with full fury and pulls hard up to ~6000 RPM. Overall it feels like a "hill" (lots of power) then a "valley" (very little power) and then a "hill."

With my limited knowledge I feel like it could be:
1. Boost control issues
2. Transmission slip
3. Throttle/drive-by-wire problems

If it were any other car, I'd keep doing WOT kickdowns for testing. But considering we're making ~320 HP now and the poor little 4T65 is doing its level best to hang on, stabbing the gas a bunch should be kept to a minimum.

Has anyone seen behavior like this with their turbo Volvo? Doesn't have to be an XC90, just trying to figure out where I should look first.
TCV
 

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Can you get on VIDA for boost reading? This will show the behavior of the wastegate actuation. With a twin-turbo set-up too, There could be inconsistencies with each turbo.

As far as new TCV, boost parameters, yes, the engine computer should have adapted by now. If you can flash back to the stock tune for diagnosis, that might help. Not knowing the tuning tables and how your specific engine was tuned (assuming logging and revision), there could be an issue as you have a new TCV now as well as the old TCV was on its way out. Wonder if logging has to be done again and the tune adjusted.
 

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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #6 ·
Thanks for the input everyone!

I installed a brand new OE Pierburg just over a month ago. I know there is some "learning" involved. I have done several WOT pulls since then as was suggested around the 'net. Does that seem sufficient? Hoses looked fine, no cracking or anything.

Can you get on VIDA for boost reading? This will show the behavior of the wastegate actuation. With a twin-turbo set-up too, There could be inconsistencies with each turbo.
I can do some logging tomorrow once she's back from the body shop. Always scary doing WOT kickdowns with the 4T65 :LOL: just waiting for that input shaft snap sound. Also worried that what I'm experiencing might be trans slip of some kind.

I know one of my turbos (driver's side) is leaking a little oil. I can hear it spool though, so I assume it still works fine. Planning on switching to high-flow billet CHRAs this summer anyways, so punting that for now. I'd check wastegate pressures but one is literally unreachable unless I remove the turbo from the car.

This tune wasn't done with revisions (waiting on a custom tune till after the high-flow, IC cleaning, and new muffler) so I suppose something could be amiss there, but it is odd that I only get this on kickdown. I don't think I've experienced this with the trans manually set to first gear.
 

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I know one of my turbos (driver's side) is leaking a little oil. I can hear it spool though, so I assume it still works fine. Planning on switching to high-flow billet CHRAs this summer anyways, so punting that for now. I'd check wastegate pressures but one is literally unreachable unless I remove the turbo from the car.

This tune wasn't done with revisions (waiting on a custom tune till after the high-flow, IC cleaning, and new muffler) so I suppose something could be amiss there, but it is odd that I only get this on kickdown. I don't think I've experienced this with the trans manually set to first gear.
Can you flash back to stock then log on WOT? Maybe you answered your own question if it only happens on kick-down and not when manually shifting down. But I'm guessing you will double check that when you get it back from the body shop.
 

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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #8 ·
Didn't have my laptop on the short drive at home but I did my best to diagnose with my ears and eyes (watching the tach).

Did a few tests from varying speeds to see what the car did when my foot went flat to the floor. I was able to sort of replicate the issue once when starting at ~20 mph. At ~4500 there was a decrease in pull (notably not completely absent), and I almost thought I heard some sort of noise when this happened. Hard to tell if it was the sound of high-pressure air venting (wooshing) or some sort of gear noise. There is no CBV (compressor bypass valve) on this motor, so it wasn't that. The tach might have moved a little but it wasn't extreme, nothing like revs jumping to 6000 with no acceleration so it was hard to tell if that was a sign of slip or not.

I took a crack at starting from 10-15 MPH and things seemed fine. She is pretty fast now...I think 10-40mph took about three seconds. Then it has to shift from 1-2 and that takes about a year (literally over a second, shift kit can't get installed soon enough). I assume this is why the 0-60 is so slow on the T6. I couldn't replicate the issue again after that, so I'll have to keep trying over the next few days.

Really hoping it isn't transmission-related, though I have had a few strange trans-related things since switching to Dextron VI from Dextron III. Not sure why as Dextron VI is apparently the new spec for the 4T65.
 

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The tach might have moved a little but it wasn't extreme, nothing like revs jumping to 6000 with no acceleration so it was hard to tell if that was a sign of slip or not.

Really hoping it isn't transmission-related, though I have had a few strange trans-related things since switching to Dextron VI from Dextron III. Not sure why as Dextron VI is apparently the new spec for the 4T65.
The logging would help with the actual boost and target. You might have again diagnosed it already, but don't want to accept the news that it could be transmission-related. :(

Ironically, I experienced transmissions that were not shifting right when using Dex VI in 4 spd transmissions from GM, ZF, and other manufacturers. When it comes to 5 spd variants, they seem to take the synthetic Dex VI much better and the Dex VI synthetic fluid is affordable in the ACDelco variety. Maybe you should go back to Castrol Dex/Merc; I've had better success with Castrol vs Valvoline. Might also be a good idea to drain the trans fluid to see if you can see any metal or unusual media.
 

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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #10 ·
Ironically, I experienced transmissions that were not shifting right when using Dex VI in 4 spd transmissions from GM, ZF, and other manufacturers.
Hm…that’s interesting evidence towards my theory about the fluid. Thanks for the info.

On my recent partial drain/refill (didn’t have the pan all the way off, just emptied about a gallon of ATF) I switched to Dextron VI. Everything I read said that it was longer lasting, had better heat tolerance, lower viscosity for better efficiency, all while providing equivalent lubrication and could be mixed with the Dextron III just fine.

Shortly thereafter (literally a week later) I got a code for a TC lock-up failure. I thought that was odd, I had NEVER had symptoms of that before. I cleared it and forgot about the issue. But now that I have these other odd occurrences…I’m starting to wonder. Strange that ALL of this would have started in the few thousand miles after the drain/refill and fluid life counter reset. Knock on wood, this 4T65 (and car in general) has been the anti-lemon. It’s the car I bring to meetups and people say, “no way, that’s an old T6!? I thought they all sucked and broke!”

As for boost behavior, I’ll do some logging on my drive to my parents place for the long weekend. Challenge with VIDA is interpreting “target boost.” I’ve been looking at TCV duty cycle…from my understanding anything above the 95% range is functionally “closed” and signals the ECM asking for more boost. This was the situation I used to have prior to the new TCV. Been tough to get confirmation on that though. I’ll let y’all know the findings, I appreciate the help theorizing!
 

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Hm…that’s interesting evidence towards my theory about the fluid. Thanks for the info.

On my recent partial drain/refill (didn’t have the pan all the way off, just emptied about a gallon of ATF) I switched to Dextron VI. Everything I read said that it was longer lasting, had better heat tolerance, lower viscosity for better efficiency, all while providing equivalent lubrication and could be mixed with the Dextron III just fine.

Shortly thereafter (literally a week later) I got a code for a TC lock-up failure. I thought that was odd, I had NEVER had symptoms of that before. I cleared it and forgot about the issue. But now that I have these other odd occurrences…I’m starting to wonder. Strange that ALL of this would have started in the few thousand miles after the drain/refill and fluid life counter reset. Knock on wood, this 4T65 (and car in general) has been the anti-lemon. It’s the car I bring to meetups and people say, “no way, that’s an old T6!? I thought they all sucked and broke!”

As for boost behavior, I’ll do some logging on my drive to my parents place for the long weekend. Challenge with VIDA is interpreting “target boost.” I’ve been looking at TCV duty cycle…from my understanding anything above the 95% range is functionally “closed” and signals the ECM asking for more boost. This was the situation I used to have prior to the new TCV. Been tough to get confirmation on that though. I’ll let y’all know the findings, I appreciate the help theorizing!
Looking forward to hearing about what you observe and perhaps getting this issue resolved.

About the duty cycle, yeah, a tuner should not let the duty cycle reach 95%+. At that point maxing out the turbo creates more heat and thus does not add power with more boost. If you don't know the tuner's target boost, then just observe the actual boost, which should follow the normal boost curve. Any fluctuations besides building up boost to dropping off at higher rpms should be noted.

Yeah, I too thought the Dex VI would work fine in 4pd transmissions using DexIII, but that didn't work out for me (Chevy SUVs, BMWs (both GM & ZF), Mercedes, Land Rover (ZF)). The 5 spd transmissions I directly used Dex VI and they work very well. The price of ACDelco DexVI is on par with Castrol Dex/Merc, so it was a no-brainer to try. But the behavior was not the same.
 

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“Dew” -- 2004 XC90 T6 in Nautic Blue
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Discussion Starter · #12 ·
Alright...have some info. Trans behaved itself on the way home and all seems well there at the moment. Hoping to drop the pan this weekend for the shift kit install, I'll check on the stuff (certain there is some) on the inside of the pan. Looking forward to smoother, faster shifts though.

Water Slope Rectangle Plot Violet


Here is a graph of TCV and boost data. This shows two separate pulls from ~20mph to freeway speeds (60 mph). Green is boost, blue is TCV.

What I find odd is that I am still seeing what is effectively a 100% TCV condition at the top end of the rev range. It certainly isn't the smoothest curve either, but I don't have much to go on. Boost looks to peak about the same in both pulls though, so it is consistent. I'm still wondering if I'm basically under-boosting given the TCV cycle vs the actual boost.

Do you notice anything odd?
 

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The TCV duty cycle looks less than 100% at the top, which is good. But yeah, agree with you with the [consistent] dip in duty cycle and boost might be an area to look at. There is a little dip in the first curve early (2nd gear?) not seen in the second curve (3rd gear?). Were you at 100% throttle in the first curve where it dips earlier on? Boost leak, turbo inefficient, vacuum leak? Might need more factors in the datalog like ignition timing (if it is being pulled), engine rpms, throttle position, fuel duty cycle if it can show it, etc. One thing from this datalog is that it appears the TCV is doing its job.

Just to check, how old are your coils? I know that higher boost R owners can go as early as 30k miles on their coils to maintain a good spark on boost. Along the same thread, have you removed and checked the condition of the spark plugs?

Or along a slipping transmission thought, maybe it is slipping a little, free-revving the engine and the TCV has to lower duty cycle to keep boost at the target. Including the engine rpm and throttle position in the logs can help show this.

Have you gone back to the tuner and ask them about the issue?
 

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Discussion Starter · #14 ·
The TCV duty cycle looks less than 100% at the top, which is good.
If I scale the graph according to TCV cycle, it does look scary close to 95% or more (hey VIDA people why no grid in the logging window??) at the peak when it is flat across the top (blue line).

There is a little dip in the first curve early (2nd gear?) not seen in the second curve (3rd gear?). Were you at 100% throttle in the first curve where it dips earlier on?
I don't live in a very rural area with good test roads so those were both 2nd gear freeway merges in auto, so you might be seeing a 3-2 kick down. I'm sure they look a little different because it was done on two different ramps with slightly different inclines etc!

After I get the shift kit installed tomorrow (wish me luck lol) I'll do some more logging with more variables (throttle position, timing, RPM).

One thing from this datalog is that it appears the TCV is doing its job.
TCV was replaced about two months ago...I guess at this point I am curious why I am seeing such high TCV cycle at high RPM. Peak output for those tiny TD03 turbos should be ~14 PSI if the ECU is requesting full boost. It's hard to read the graph but...doesn't look like 14 PSI to me. Coils are in good shape (most ~50K miles old) and plugs have 1-2K on them. I suppose I could totally still have some sort of boost leak or turbo issue?

I wish I had a tuner for support but this was one of VDASH's "optimizations." I talked to them about it a little. One interesting thing to note: they mention turning up the wastegate pressure from 4.7 PSI stock to 6.3 PSI after the tune. Wonder if that is part of the issue?

Thanks again for all the help mate :)
 

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I wish I had a tuner for support but this was one of VDASH's "optimizations." I talked to them about it a little. One interesting thing to note: they mention turning up the wastegate pressure from 4.7 PSI stock to 6.3 PSI after the tune. Wonder if that is part of the issue?

Thanks again for all the help mate :)
I see why you cannot get a good log now. It's not a regular tuner like Hilton who has software to log.
Oh, that information is important pre-setting the wastegate to a higher psi. Go get a vacuum tool to adjust the wastegate. Besides the tool, that's a free adjustment for the wastegate actuator arms.
A start for the process. Sorry if the video is large. Don't know how to resize the automatic embed videos of the forum:

 

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Discussion Starter · #16 ·
Oh, that information is important pre-setting the wastegate to a higher psi. Go get a vacuum tool to adjust the wastegate. Besides the tool, that's a free adjustment for the wastegate actuator arms.
I think I'll have to pull the turbos to get to the actuators, at least for the passenger side turbo. Volvo had a moment of engineering...brilliance and opted to put the actuator/arm facing down towards the road surface. I'll give it a college try when I have the car up tomorrow but it will undoubtedly be hard (nigh impossible) to get to. Do you think that ~1.5 PSI increase would potentially alleviate or lessen the ~95% TCV condition? Wonder if I am still under boost target by a bit and that's part of the weird issues I am having.
 

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All possibilities. Wish the tune was better understood and more info was given to you. At least if they could provide a way to datalog.
 

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Discussion Starter · #18 ·
Funny thing is that VDASH is supposed to provide a logging feature that seems vastly superior to VIDA...except it doesn't work for my car. No idea why.
 
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