Not sure whether I have a problem or not, so I

f I explain the symptoms maybe somebody brighter than I can diagnose the cause...

History... Octavia II vRS PD 170. 07 plate, 68k miles. Just (a couple of weeks ago) had major service and cambelts changed. No change to use of vehicle or manner of driving. I've owned the car since it had 6000 miles on it and never encountered this issue.

The problem...

Low revs (say below 1800-2000rpm), 6th gear, try to accelerate and met by power, then a thumping loss of power, then the torque comes back in, then drops right off again. Change down to 5th and all is well. Try to recreate the situation at lower speed in a different gear by deliberately labouring the engine and it behaves exactly as normal - accelerates through the low rev range and then takes off.

Gut reaction says turbo, but the fact that it only happens in 6th makes me wonder about electronics, rather than mechanicals.

Other than this it continues to drive fine. No warning lights.

One other thing - the fuel economy seems to have dropped by about 8-9mpg according to the onboard computer. Might be connected?

Thoughts please - something and nothing, or needs dealing with?

Phil

It's not really ideal trying to accelerate in those circumstances anyway, if you want to accelerate from that point select 5th or lower, then proceed.

Aside from that, you should just get no power to start with, as the turbo's just coming onto boost, then probably some vibration as the flywheel has to handle the influx of torque in that gear, then you should start moving normally as the turbo is now on-boost and providing assistance. But the fact that some power is being delivered, then tailing off, seems to suggest that the turbo isn't able to supply the required level of boost. Or if it's interrupted as you describe, there could possibly be a DMF issue there, that the engine's output isn't able to successfully travel through the transmission and reach the driven wheels.

Initially I would look to see if any error codes have been logged.

Hard to say without driving it, or experiencing it directly. But as you're not finding an issue elsewhere in the rev range, or with other gears, I would 'drive round' the issue. Which, as I say, is the best course of action anyway, rather than expecting the car to pickup from off-boost in the highest available gear.

From a novice I cant see how it can be electrical as the car only measures load etc, I dont think the ECU knows what gear the car is in

Did it become noticable imediately after the cambelt was changed, if yes has that been done properly, we had one changed on a mondeo a few years ago, moaned like xyz to the gargae the car just felt wrong but they were adament it was OK, we had a long row with the lease company who agreed to use a different garage to check it & the belt was 2 teeth out

Not sure whether I have a problem or not, so I

f I explain the symptoms maybe somebody brighter than I can diagnose the cause...

History... Octavia II vRS PD 170. 07 plate, 68k miles. Just (a couple of weeks ago) had major service and cambelts changed. No change to use of vehicle or manner of driving. I've owned the car since it had 6000 miles on it and never encountered this issue.

The problem...

Low revs (say below 1800-2000rpm), 6th gear, try to accelerate and met by power, then a thumping loss of power, then the torque comes back in, then drops right off again. Change down to 5th and all is well. Try to recreate the situation at lower speed in a different gear by deliberately labouring the engine and it behaves exactly as normal - accelerates through the low rev range and then takes off.

Gut reaction says turbo, but the fact that it only happens in 6th makes me wonder about electronics, rather than mechanicals.

Other than this it continues to drive fine. No warning lights.

One other thing - the fuel economy seems to have dropped by about 8-9mpg according to the onboard computer. Might be connected?

Thoughts please - something and nothing, or needs dealing with?

Phil

As a noob to this world, is your engine a 2.0 litre by any chance. The reason I ask is that I know that the 2 litre engines use piezo electric injectors which come with a couple of little problems. There have been instances of a single injector giving up the ghost around 100,000 or just before. Because of the way the ECU reads the feedback from the engine, if one injector fails, the ECU can shut the whole engine down, happened on a friends Audi 2.0L. He was lucky as he was in the outside lane of a motorway at the time and just managed to coast to the hard shoulder. It's possible that the injector(s) could be poorly sick and about to give up the ghost.

Has it been remapped? Does it happen if you gently accelerate in 6th from those revs or only if you accelerate quite hard, suddenly?

Last year, as my turbo started to fail, my PD170 behaved just like this.

This was the boost control behaviour on mine during one of the power drop outs on starting to accelerate (right after the first steep drop off on the blue rpm line where I change gear - power loss happened when I got back on the power hard when I changed up to the next gear)..

That's actually not terribly helpful - mainly because VCDS doesn't get to see what' happening boost wise above 1.6bar so the MAP value on the graph tops at at 2600. Anyway, in my experience, the issue is caused by a mapping problem (if you've had it remapped) or a turbo starting to fail. The weird thing was my VNT mech seemed to be free moving (I thought it would be sticking, given the erratic boost), my N75 was perfect, when the dealership checked the turbo there was quite a bit of play in the shaft.

As time went on it got harder and harder to accelerate in 6th without provoking the problem. New turbo under warranty and it was fine again.

Thanks for all comments. I'm not stamping hard on the throttle at low revs in 6th, the problem's showing itself on a neutral or very slightly positive throttle in 6th. Where I'm encountering it in normal driving is when motorway traffic slows (say to around 55-60mph or so) and then starts to flow again. In gently putting the throttle down (without changing out of 6th) it's then that it's stuttering and faltering and making me go down to 5th where before it would simply deal with it and grunt on through.

And no, not remapped, although I have been thinking about it...!

From what Nick's said, that does sound pretty similar.

And I now understand more about how you're using 6th gear and under what circumstances. Makes full sense to me and I agree; it should not respond in the way it's doing....

As a noob to this world, is your engine a 2.0 litre by any chance. The reason I ask is that I know that the 2 litre engines use piezo electric injectors which come with a couple of little problems.

Just for info, and for others viewing the thread - it's the PD170 version of the 2.0TDI that uses piezo injectors, the PD140 has a different arrangement.