V70r Occasional hesitation, bypass valve?

dave88sw · Aug 24th, 2019, 20:09

Hi,

I have a 98 V70R. A couple of months ago I had an over boost problem which led to a bent con rod. I have completely rebuilt the engine with forged rods and replaced the TCV which I think was the cause of the problem and it's running well. That is, except under load, occasionally it seems to build boost, then hesitates before picking up again. The problem seems to be worse the longer I drive and when its showing these symptoms I do seem to hear the turbo a bit more than usual. There is no play in the turbo shaft and no excess oil in the intake. Would this point to the bypass valve sticking, or a torn diaphragm?
If so, any UK based suppliers? Or is it dealer only?

Many thanks
Dave

SteveSarre · Aug 25th, 2019, 13:43

Hi Dave

Is your car Auto or Manual (but not sure that that makes any difference)?

Do you have access to the Volvo VIDA Dice diagnostic tool?

Are you able to live monitor the boost pressure and also the TCV duty cycle (the % of time that the TCV is activated - this happens up to 50 times per second)?

I would check all vacuum hoses very thoroughly.

I recently had what might be described as occasional hesitation which turned out to be a combination of things.

Steve

SteveSarre · Aug 25th, 2019, 14:25

PS

And check your vacuum check valves.

https://www.volvoforums.org.uk/showt...um+check+valve

Over the last few weeks I have tested about 6 valves and found 4 to be faulty.

Note the direction of the arrow before you remove them, then blow through them in each direction. One way should flow easily, the other way should close quickly.

Faulty ones either don't close at all, or sound like a kazoo (buzzing rather than closing completely).

HTH
Steve

PNuT · Aug 25th, 2019, 16:39

MY 98 will need VOL-FCR!

doesn't sound like the diaphragm to me, it will just run fine at lower boost than it should....

Cookeh · Aug 26th, 2019, 08:32

I'd agree with PNut, a bad diaphragm shouldn't result in hesitancy, just a lower boost pressure. I would be looking for vacuum leaks and boost leaks. I'd also check the boost hoses to see if they're deforming under boost. The soft joins can and have degrade to a point that under boost pressure they collapse. Which would give the symptoms you're describing. Robert DIY has a video on this.

May I also ask where you got your new TCV from? I think mine is due for replacement.

Gaztech · Aug 31st, 2019, 08:40

I had this same problem exactly as you describe. New distributor, leads and plugs. Problem gone

Aug 24th, 2019, 20:09	#1
dave88sw Junior Member Last Online: Dec 10th, 2023 08:37 Join Date: Oct 2013 Location: bath	V70r Occasional hesitation, bypass valve? Hi, I have a 98 V70R. A couple of months ago I had an over boost problem which led to a bent con rod. I have completely rebuilt the engine with forged rods and replaced the TCV which I think was the cause of the problem and it's running well. That is, except under load, occasionally it seems to build boost, then hesitates before picking up again. The problem seems to be worse the longer I drive and when its showing these symptoms I do seem to hear the turbo a bit more than usual. There is no play in the turbo shaft and no excess oil in the intake. Would this point to the bypass valve sticking, or a torn diaphragm? If so, any UK based suppliers? Or is it dealer only? Many thanks Dave

Aug 25th, 2019, 13:43	#2
SteveSarre Premier Member Last Online: Apr 17th, 2024 17:43 Join Date: Oct 2004 Location: London/West Country	Hi Dave Is your car Auto or Manual (but not sure that that makes any difference)? Do you have access to the Volvo VIDA Dice diagnostic tool? Are you able to live monitor the boost pressure and also the TCV duty cycle (the % of time that the TCV is activated - this happens up to 50 times per second)? I would check all vacuum hoses very thoroughly. I recently had what might be described as occasional hesitation which turned out to be a combination of things. Steve __________________ V70 2.5 Turbo AWD Man. 1999 Red V70 2.5 10V Auto 1998 Green C70 T 20V Auto Conv. 2001 Blue, C70 T5 Auto Conv. 2000 Blue V70 2.5 Turbo AWD Auto 1998 Green, V70 2.5 10V Auto BiFuel 1999 Red (scrapped) V70 20v Auto 1999 Green (scrapped)

Aug 25th, 2019, 14:25	#3
SteveSarre Premier Member Last Online: Apr 17th, 2024 17:43 Join Date: Oct 2004 Location: London/West Country	PS And check your vacuum check valves. https://www.volvoforums.org.uk/showt...um+check+valve Over the last few weeks I have tested about 6 valves and found 4 to be faulty. Note the direction of the arrow before you remove them, then blow through them in each direction. One way should flow easily, the other way should close quickly. Faulty ones either don't close at all, or sound like a kazoo (buzzing rather than closing completely). HTH Steve __________________ V70 2.5 Turbo AWD Man. 1999 Red V70 2.5 10V Auto 1998 Green C70 T 20V Auto Conv. 2001 Blue, C70 T5 Auto Conv. 2000 Blue V70 2.5 Turbo AWD Auto 1998 Green, V70 2.5 10V Auto BiFuel 1999 Red (scrapped) V70 20v Auto 1999 Green (scrapped)

Aug 25th, 2019, 16:39	#4
PNuT MaDMaN Last Online: Nov 26th, 2022 18:47 Join Date: Sep 2006 Location: Red Lodge	MY 98 will need VOL-FCR! doesn't sound like the diaphragm to me, it will just run fine at lower boost than it should.... __________________

Aug 26th, 2019, 08:32	#5
Cookeh Premier Member Last Online: Sep 14th, 2022 17:04 Join Date: Jan 2018 Location: Derbyshire	I'd agree with PNut, a bad diaphragm shouldn't result in hesitancy, just a lower boost pressure. I would be looking for vacuum leaks and boost leaks. I'd also check the boost hoses to see if they're deforming under boost. The soft joins can and have degrade to a point that under boost pressure they collapse. Which would give the symptoms you're describing. Robert DIY has a video on this. May I also ask where you got your new TCV from? I think mine is due for replacement. __________________ 1995 Volvo 850 T5 Estate (Manual)

Aug 31st, 2019, 08:40	#6
Gaztech Member Last Online: Apr 15th, 2024 20:13 Join Date: Dec 2018 Location: Glasgow	I had this same problem exactly as you describe. New distributor, leads and plugs. Problem gone

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