XC70 D5 bunnyhopping, loss of MPG and power and soot filter

[mjk164]

Hello all,

2005 XC70 D5, 187000 miles.

For a few weeks now, there's been occasional rough running and a small loss of MPG. Now on some trips, there are no issues at all but in the past 10 days or so, the occasional rough running has progressed to 'bunny hopping' like a learner driver as the power delivery is so lumpy, MPGs are down to about 38, when the turbo does kick in there is a 'hissing' sound on top of the usual noise (but it's still plenty powerful, until it suddenly won't rev). Sometimes there is a loss of power (just like before I replaced the intercooler a few months back) especially when demanding power after a steady run, such as approaching a motorway hill and on most journeys now 'soot filter full see manual' appears on the dash.

The first time that happened, I took it for a 20 minute run at 4000rpm and all went back to normal, including MPGs building back up to 40 but then the message appeared again the next trip.

I don't have VIDA but a generic code reader says there are no fault codes stored, which has to be untrue. This car is used almost exclusively for long motorway speed journeys so the 'short, not fully warmed up' problems surely won't apply. There is also a long standing 'engine system service required' message but until now has not been associated with other symptoms. The engine management light is NOT on though.

My research so far suggests the DPF is at fault, with a forced re-gen at a dealer perhaps being needed. My nearest one wants £99 for a diagnostic check and then £160 odd for a re-gen if this is the case but they are some distance away.

Are there any possible causes and fixes to look at here before I commit to gong to the dealer?

To rule things out, the diesel filter was changed recently, the IC is basically new, the MAF has been thoroughly cleaned with MAF cleaner and dried, and I cleaned out the EGR and pipework this week. They weren't bad at all but didn't solve the problem.

Please could anyone suggest anything else I could look at myself?

Thanks

[mjk164]

Just adding, when you drive with Windows down there's a rich diesel smell and a thought- could this be the clutch? Just now there was a lot of clanking coming from the drive train and the bunnyhopping could be clutch?

[John97Tdi]

The D5 engines have a turbo anti resonator pipe that consists of a 'dog leg' plastic pipe which is secured by two orange seals in the turbo pipework running front to back under the middle (ish) part of the engine - the seals often give way slightly under boost and can then reseat themselves giving intermittent problems( 'bunny hopping' being one). Mine was definitive when it failed in that it disconnected completely. You can replace the dog leg section with a simple pipe from ebay for about £30 or the seals alone for about a tenner. I replaced the resonator on mine about 2.5 years ago and had no problem since. Easy to check once you get the undertray off and grovel under the car and look up, but actual removal and refitting can be a PITA due to access - yours may be easier with being a manual.