Engine: T5: Surging acceleration / vacuum advice.

[7 Seat Sports Car]

Under 3k rpm is where everything seems a.ok.

This is gonna be tricky to explain.

For any given throttle position the engine has a finite rpm it will achieve and if i allow the engine to reach its max for that given position and then slowly accelerate it from there so the engine speed is never that far behind my throttle demand then the engine accelerates smoothly with no problems that are noticeable.

However when i mash the pedal to the floor and then wait for the engine speed to respond it will accelerate quickly as you'd expect from a T5 and at random times between 2800 rpm right through to the red line it will pause then resume then pause then resume the hard accel.

The revs don't stop climbing and don't pause either. It never happens at a specific rpm nor does it happen the same number of times every time i do this. Sometimes it stutters twice, sometimes it porpoises its way to the gear change. Sometimes, usually in 2nd off a roundabout, it doesn't misbehave at all. This is quite rare though.

Bizarrely, things are less noticeable after 4k rpm which i believe is the point at which the vvt pulley rotates. The acceleration pulses then either pulses less or not at all after this point.

I initially thought it could be the TCV and for a tenner from my local volvo knackers yard it was worth a punt. Either this one and the old one are both duff or it is somthing else. £50 for a new one is a tough gamble when that 50 quid could be halfway to the cost of a replacement turbo or fuel pump or whatever.

Does this make any sense to anyone. Apologies if it sounds difficult to grasp.

[7 Seat Sports Car]

Oh, missed a bit.

The car has travelled 176k miles.

Spark plug gap is between 0.7 and 0.75 mm. They are two of the prong sizes on my gap feeler gauge and they worked as a go-no go gauge for me. Good times.

The last code to be read was related to coolant temp sensor and that was over a year ago. Not had anything since.

[deathrider311271]

sounds like boost cut to me, to be sure it is this you would need to install a boost gauge and get someone too keep an eye on it while you floor it.

But as 960 says it could also be the fuel pump.

[7 Seat Sports Car]

I can hear the turbo winding up (whooshy kinda noise) and when the accel pauses so does the whooshy noise. As i have noticed no pause in the needles climb i can only assume that the engine itself is still accelerating but something slows the turbo down.

I would assume that the turbo is original and thought a couple of things:

1. that the bypass valve might have a bit of a wibble and allow boosted air to re-circulate to the front of the turbo briefly;

or;

2. seals inside the tcv are guff and air gets past regardless of solenoid position and gives the wastegate a quick nudge.

[960kg]

Originally Posted by 7 Seat Sports Car

I can hear the turbo winding up (whooshy kinda noise) and when the accel pauses so does the whooshy noise. As i have noticed no pause in the needles climb i can only assume that the engine itself is still accelerating but something slows the turbo down.

I would assume that the turbo is original and thought a couple of things:

1. that the bypass valve might have a bit of a wibble and allow boosted air to re-circulate to the front of the turbo briefly;

or;

2. seals inside the tcv are guff and air gets past regardless of solenoid position and gives the wastegate a quick nudge.

Secondhand TCV`s are never a good thing as one doesn`t know there condition as you are thinking the same, but to see if it is faulty just take off the hose which has the red marker on that goes to the TCV and the turbo will have full boost but not to detrimental effect as the ECU controls the max. the TCV just controls how much boost and when up to the max.

As one appreciates it is very difficult being a keyboard mechanic to try and help members
At 176,000 it won`t harm to do as i do and that is use a fuel system cleaner in the fuel tank and i used to swear by Wynn`s or STP products until it was suggested "just wait until you try this", well, this was BG44K and it`s here on ebay, give it a try and even after about 50 miles it does have a big effect on performance as it cleans all the crap out including getting the fuel injectors back there correct spray pattern. You will be very surprised what it does, i have used it on my T4 and now this V70 T5 at 158,000
Ok so it`s expensive but not for once every 12,000miles

[AndrewandKirsty]

Hi - reading these posts today with great delight as it seems I'm not the only one in the world with these problems! Much the same, with gentle acceleration the car pulls all the way through the revs, but boot it in any gear and it gets to between 3k and 4k and seems to "missfire". Can make a sharp overtake with kickdown an interesting experience....

Plugs are new genuine volvos and leads/coil all appear to be fine. Air filter clean, oil brand new and so on. I too have heard (can't remember where) that vacuum lines can be an issue so I will be changing these as they are all original and looking a bit past it. But have also heard that this can be down to fuel filter issues (starvation on heavy demand?), wastegates sticking and so on. My last mechanical experience was way back with a 3 litre Capri so it's ancient and basic to say the least! This car has been in the family for nearly 10 years and is worth next to nothing value wise and though we do love it I'm again looking for a cheap solution rather than putting £££'s in without knowing how to solve the problem.

Will let you know if changing the vacuum lines makes any difference though I'm putting it off as the thought of working in the street in the cold isn't filling me with joy......

[7 Seat Sports Car]

Originally Posted by AndrewandKirsty

Will let you know if changing the vacuum lines makes any difference though I'm putting it off as the thought of working in the street in the cold isn't filling me with joy......

I hear you. -2 yesterday so decided internal home improvements were the way forward. Put a new floor down in the kitchen/diner.


960;

Thanks for your recommendation. Already thrown a bottle of wynns through it. Got economy from 24.5 to 25 mpg up to just above 26 and i'm just at the end of the tank with the wynns in it. Will get some of that BG44K and give that a whirl. Was gonna try the fuel pump filter that you mentioned. I figured it would be a course gauze filter and unlikely to hinder the flow that much so discounted it. You should see the state of the aircraft fuel filters I remove from time to time.

[960kg]

You`ll find it a fine mesh, it also has a one way valve in there to grab the fuel as it rushes past the pump which is in the plastic pot. When you accelerate hard and up long steep hills with a low tank of fuel the valve keeps the fuel in the pot so the engine has no starvation. You really have to look for the valve as it is in the mesh and of course the same blacky colour from the dirty fuel.

[anth]

Sounds much like my car, I have been told it is the turbo blow off valve which I have just bought of ebay for £40.

[Nightmare1971]

I too have this problem, it happened to my 1998 V70 T5 145,000 auto on the way home tonight for the first time, the only thing I did different was turn off the traction control 2 miles before it played up, it has 1/4 of fuel and I haven't lifted a spanner to it in over 12 months...

I might even open the bonnet this weekend for a look see......