[LittleRedRidingHood]

Hi All,

A couple of days ago my 2007 S40 T5 AWD suddenly lost all its top-end power (3.5k RPM and up), and has driven the same ever since. Low end torque is still pretty good (although maybe not 100% of what is used to be), and top-end feels as though it's less than what a naturally aspirated 2.5L 5-cyl would have.

Here's a list of some relevant info:

• Can still clearly hear the turbo spooling up
• Turbo is whistling louder than usual, but no obvioius 'dumping' sounds
• Gear changes are off - sudden and rough changes
• It seems like the engine is cutting the timing to protect itself. I thought when I went to a full-service gas station they may have put regular gas in, but I no longer think this is the case and have been through close to a half tank of premium now
• While accelerating at higher RPMs revs will sometimes even drop a little bit, not consistent pull
• The car starts and idles perfectly
• No CEL or other warnings - battery seems to be fresh as it only cranks once or twice before starting
• I don't push the car until it's fully warmed up, so I don't know if this develops as the car is driven for longer

Any ideas as to what this might be? I've done some reading and TCV seems as though it may be the culprit, but not totally sure. Thanks!

These threads seem related:
http://forums.swedespeed.com/showthread.php?228028-Limited-Boost-Pressure-Bad-TCV-Other
http://forums.swedespeed.com/showthread.php?163933-Unsolved-problem-getting-expensive-2005-S40-T5
http://forums.swedespeed.com/showthread.php?206702-Failing-turbo-control-valve

 

[JN2k108]

what's your boost gauge say?

 

[LittleRedRidingHood]

I do not have a boost gauge. Do you think it is a boost leak?

 

[JN2k108]

Can't tell if you don't have a boost gauge. Have you reset the ecu?


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[LittleRedRidingHood]

No, I haven't. Does that involve just disconnecting the battery for a while? I've read holding the terminals together for 3 minutes may be part of the process. Is that all that's required for an ECU reset?

 

[AviatorDrew]

You could check the rubber hoses for cracking or pinholes.

 

[avenger09123]

if you're hearing the whistle louder than normal, it means there's an air leak somewhere. Probably only opens above the PSI and closes when you go below that PSI.

 

[Shaun42073]

Just because your check engine light is not on doesn't mean theirs no codes stored. Do you know how to check if theres codes stored with the fog light button and the trip comp. reset button ? If not google it I'm sure its out there.

 

[LittleRedRidingHood]

Thanks for the info, everyone!

I was able to fix it by resetting the ECU. I reset the ECU by disconnecting the negative battery terminal, ensuring all charge is out of the system, then reconnecting while the key was in position II. I then idled in N for a minute, then in D for a minute, then gently accelerated until the car shifted into 5th (auto trans), then downshifted through the gears and came to a stop. Not sure if this full procedure was necessary, but it's what I found from someone who apparently saw this procedure listed in the technical manual for the car.

Shaun, thanks for letting me know about the information on how to see if there are any stored codes. I will check that next time I'm in the car, as even if there aren't any noticeable problems any more it will be good to know for the future. Seems to be making full boost now, so I don't think I have a leak, but still probably worth checking.

 

[LittleRedRidingHood]

After a week of the issue being resolved, it is back again. I tried the same steps to reset the ECU, but this time to no avail. I really don't think it is a boost leak as I don't see it would have sealed up for a week and then come back, and I don't think the first ECU reset seeming to fix the issue was just a fluke.
Is it possible that the first ECU reset was enough to bring life back to a failing TCV and it is going bad again?

 

[m4gician]

Fuel pressure sensor?

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[TG]

After a week of the issue being resolved, it is back again. I tried the same steps to reset the ECU, but this time to no avail. I really don't think it is a boost leak as I don't see it would have sealed up for a week and then come back, and I don't think the first ECU reset seeming to fix the issue was just a fluke.

Is it possible that the first ECU reset was enough to bring life back to a failing TCV and it is going bad again?

No . . . and I very much doubt resetting ECU would fix any form of power loss. At best it might reset your driving habits which could give you a placebo effect, but it doesn't sound like that's what it is.

If you're car isn't in a limp mode (which would pop a CEL) that would more frequently point to a boost loss which could be the TCV, an air leak in the system, a failing turbo or blow-off valve. There are other things that could affect engine performance drop, but usually those would pop a CEL I would think...

 

[LittleRedRidingHood]

No . . . and I very much doubt resetting ECU would fix any form of power loss. At best it might reset your driving habits which could give you a placebo effect, but it doesn't sound like that's what it is.

If you're car isn't in a limp mode (which would pop a CEL) that would more frequently point to a boost loss which could be the TCV, an air leak in the system, a failing turbo or blow-off valve. There are other things that could affect engine performance drop, but usually those would pop a CEL I would think...

Thanks for the info. It definitely wasn't a placebo effect - the car went from a butt-dyno reading of about 80 horsepower (barely able to accelerate at highway speeds) to returning to full performance. I reset the ECU three times yesterday and each time the engine had very unique changes in characteristics - change in boost pressure / point of reduced boost in rev range, power, etc. Definitely no CEL's to speak of so far. I don't think it is a failing turbo as I can always hear lots of boost being made. Failing TCV or blowoff valve sound the most likely, or the fuel pressure sensor as m4gician mentioned.

Are there any diagnostics I could do with a run-of-the-mill OBDII scanner, or is ViDA + DICE required for our cars to get any relevant information?

 

[theshadow27]

Get yourself a DiCE, it's cheaper than one diagnostic visit to a stealership.
E.g. http://www.ebay.com/itm/VOLVO-VIDA-...-/231786150078?hash=item35f787f8be:g:3HsAAOSweW5VOBKD&item=231786150078&vxp=mtr

 

[LittleRedRidingHood]

Thanks, I am going to order a DiCE. I checked for OBDII codes and there are none stored - I'd assume there must be something logged by the computer in this scenario so hopefully VIDA + DiCE will help.

 

[LizardOfBodom]

Hi
I had exactly the same symptoms that were related to low tyre pressure in one of the wheels. It sound stupid but actually happened (and keeps happening as I have slow puncture). No "life" in higher revs, very rough gear changes etc - its the stability sensor trying to overcome few PSI difference. No CEL either, although it does display the speed sensor fault when OBD2 reader connected.
When you disconnected the battery, you also cleared out all faults - same as I do it when manually clearing the fault using my reader - car imediatelly comes back to life when I do so.
Cant say your fault is exactly the same, but symptoms are definetely similar.
Other issues I had with lack of power (TCV broken, and control valve faulty) made car constantly underpowered so that was the only fault that was purely dependadnt on car's "good humour" :]

ps - its not only tyre pressure that causes that - faulty bearing, uneven tyre thread or something wrong with ABS sensors - basically anything that can make the car "think" one of the wheels is rotating in different speed and hence car may skidding.

 

[LittleRedRidingHood]

Hi
I had exactly the same symptoms that were related to low tyre pressure in one of the wheels. It sound stupid but actually happened (and keeps happening as I have slow puncture). No "life" in higher revs, very rough gear changes etc - its the stability sensor trying to overcome few PSI difference. No CEL either, although it does display the speed sensor fault when OBD2 reader connected.
When you disconnected the battery, you also cleared out all faults - same as I do it when manually clearing the fault using my reader - car imediatelly comes back to life when I do so.
Cant say your fault is exactly the same, but symptoms are definetely similar.
Other issues I had with lack of power (TCV broken, and control valve faulty) made car constantly underpowered so that was the only fault that was purely dependadnt on car's "good humour" :]

ps - its not only tyre pressure that causes that - faulty bearing, uneven tyre thread or something wrong with ABS sensors - basically anything that can make the car "think" one of the wheels is rotating in different speed and hence car may skidding.

Thank you for the insight, LizardOfBodom. Sometimes it's the simple things.. I have a slow leak in the rear passenger side tire which I haven't topped up in almost 2 weeks as well as some uneven tread on my front passenger side tire. I'm going to see if the low tire pressure is the culprit tomorrow - I have a hunch that it might just be.

Good to know that the TCV, control valve, bearings and ABS sensor could cause issues if it's not the tires.

 

[LizardOfBodom]

.. I have a slow leak in the rear passenger side tire which I haven't topped up in almost 2 weeks ...

good luck, fingers crossed, that would be cheapest repair possible :]

 

[LittleRedRidingHood]

good luck, fingers crossed, that would be cheapest repair possible :]

Unfortunately this doesn't seem to have fixed it. I may go back and make sure my tire pressure measurements are spot on later. Car wasn't giving any OBD2 codes and trying a code clear didn't help.

 

[LizardOfBodom]

Unfortunately this doesn't seem to have fixed it. I may go back and make sure my tire pressure measurements are spot on later. Car wasn't giving any OBD2 codes and trying a code clear didn't help.

Maybe its not it then What about your bearings and springs&shocks? All in good condition?