somersetlemon

Hi, new here, although I think I might have been around 3-4 years ago.
That was when I bought my 60 plate Legacy Diesel SE.

Generally I have been delighted with the car, and would love to keep it, however I have had, since new, problems with what I regard as excessive fuel consumption and some rough running. Wondering if anyone else has similar experience or advice.
The car has been serviced on time at Vale Motors Wincanton where I bought it, and is now 3 1/2 years old with 51k miles. I have had only one problem, which was a DPF issue. Warning lights came on and the car ran very rough and slow. I got it recovered and was fixed under warranty.

The problem I have had is that the engine map seems to vary all the time. Most of the time the car is creamy smooth, reasonably powerful/quick and the fuel consumption is acceptable (38-40 mpg let's say). Every now and again, you notice a lack of power, the engine feels ever so slightly rougher, and you notice the fuel consumption going up markedly. You can see this by the average mpg on the computer, the fuel gauge, and the mpg meter and it is very noticeable. It can go down to 30 or so mpg quite easily. I call this the "crap map". This was happening a few times a week, after a while it would go back to normal, and eventually I found that if I turned the engine off, counted to 10, and re-started it would reset back to normal. If you are cruising on the motorway with cruise control, you only notice this by the fuel consumption, where the difference is very noticeable.
Most of my miles are cross country B roads, with only the occasional motorway trip and very little town driving. Therefore I am using the gearbox a lot and the engine does get revved.
I have complained about this at every service, and i think they have updated the software at least once. The mumbled something about the software "learning" differently now. They also changed the fuel filter at the last service as there was a suggestion of moisture. When I got the car back it felt fab, for about 200 miles, and then reverted to its bad old ways. Now it does it every day, and the first time typically around 15 minutes after starting a journey. It is like a switch when it happens and if you are overtaking or pulling out of a junction at the time it is slightly alarming. If you are just cruising along you would not notice it. When accelerating though, the power loss is a lot, at least 20%-30% I would say, and it almost feels like the handbrake is partly on.
I thought for a while it was a DPF issue, but I don't think it is now, unless there is a faulty DPF sensor or something (there must be something to tell it when to burn off the particulate?). I have only noticed smoke from the exhaust once in all the time I have been driving it.
The fuel consumption cross country is a little high, I can get 37-39 mpg, especially if I turn the engine off to reset quickly, but I am not hanging about and it is hilly and complicated driving. The motorway MPG though is very disappointing. Cruising at 75 on the level I would expect to get 50+ mpg but the best I have ever seen from this car is 45. Others seem to do much better than this.
So what do you think? I just wish the engine setting would stay the same as when I start it up. Maybe there is some software I could get aftermarket now it is out of warranty? I don't need more power. Any experts to talk to? Vale motors are no longer a Subaru dealer so I am not sure about going back to them yet again (although the dealer experience has been good there in fact)
Thanks in advance

Jim

PS the engine is quiet and doesn't use any oil.

1509joe

iTrader: (2)

Sounds like a DPF regeneration problem. When regenerating you will experience a loss in power in any diesel car it is a terrible system and idea. If you do a lot of slow or medium speed driving it will not regenerate it needs to be on the motorway for a period of time at x amount of revs and x amount of time and x temperature. If you wish to keep it get it removed and mapped out of it. Not the ideal solution but it works. Certain manufacturers won't sell diesel vehicles to people for the likes of the school run now because they were sick of replacing DPFs under warranty.

somersetlemon

Thanks, but I am not convinced this is it, as I am not just doing school run. My normal journey to work is 40 miles on B roads up and down hills and is regularly revved, full power used etc. I am not hanging about and do very few short journeys.

When I do do long motorway runs, it does not improve.

When I thought it was a DPF problem I tried running over 3000 revs for 10 miles as recommended by the AA (this is what they do if called out to a DPF issue apparently). This made no difference to my problem. It is not easy to do this on a Diesel as it basically means running on the motorway in 3rd gear, although the engine is pretty smooth and you do get used to it! Interestingly when I did this it made very little difference to the fuel consumption. I got the same roughly in 3rd or 4th gear at 70 mph as I do in 6th gear!! Something wrong there surely?
Any recommendations for someone to take out the DPF and remap? Does this not affect the MOT?

Why would it regenerate 2-3 times a day? How often should it be doing this?

scoobyboy

it could also be its trying to recalibrate the injectors, they will after a certain mileage cut each injector out in turn so it can work out the optimum injection for each one. it will carry out the process but if you drive off it will cancel it out then retry when conditions are right again.

somersetlemon

Well, I have just done a long motorway trip in it, around 350 miles M5 and M6, mostly cruising at around 80.

Still having problems. I stopped at Frankley for fuel and zeroed the mileage to restart the average fuel consumption. For the first 20 or so miles, which included moderately heavy traffic through Brum, I got 53 mpg, which is the best I have ever seen and shows what the car could do. Then it started playing silly beggars again and by the time I got to St Helens it was down to an average of 42. I did try running in a lower gear for about 20 miles, at around 3000 rpm, and the engine did clear for a while.
Coming back, I was in a queue near Knutsford and the DPF warning light started flashing. It last did this nearly 2 years ago. It was reduced power and high consumption again, so again when I could I tried running it in a lower gear for a while. This got the consumption down to around 40, but it cleared, although the light was still flashing. Rest of the journey it seemed to be running fine and overall average recovered to 43 mpg (this is probably more like 41 mpg in reality as the computer is around 2 mpg optimistic). The light stayed flashing all the way home and then finally switched itself off on my drive. I have restarted the car a couple of times and the light has stayed off.
So I am back to thinking the fault is associated with the DPF, and maybe for some reason it is failing to regenerate properly, and keeps trying to do it several times a day.
Anywhere I could go with this other than back to my dealer again?

Thanks

Jim

rob84

iTrader: (5)

for starters the regeneration procedure you have been told is incorrect.

2500 rpm or 4th gear 45mph for 30 minutes. is enough to put the engine into a lean burn condition to clear the soot accumulation within the DPF.

as for the fuel consumption there are a couple of things in which the dealer could have done and one of which is perhaps why the car isn't behaving as it should.

If the car has been recovered in with warning lights illuminated and the dealer has just done a clear memory rather than OBD clear they will have wiped all of the learnt fuel data.

Get you dealer to make sure the MAP sensor in the intake is clean and free of gunge.

clear the memory.
Carry out a Fuel pump duty cycle learning
followed by a Fuel Injector duty learning
if you find the fuel pump wont learn, carry out a fuel injector learning duty then go back and try the pump duty again then the fuel injector duty learning.

This will set the car back up to base settings and stop the crap fuel consumption.

Next up carry out a turbo geometry learning as your is the euro 5 engine the laptop will allow this, If you find it cannot complete I'd put money on the turbo actuator pin being partially seized, this will cause a multitude of issues.

pacenote

^ This man's on the money..

Don't think I've ever seen 50+ mpg on mine, best is high 40's, average is prob mid 30's. Mind, I don't have DPF problems as being 1st generation car.

scoobyboy

weren't those ones supposed to be changed at a set mileage as they didn't have the option to do a regen?

rob84

iTrader: (5)

supposed to be around 100k or 10 years