I had my Mk2 2.0 TDi (55 plate BKD c.140k) Octvia serviced at a main dealer just over a month ago and since then the fuel economy under acceleration has been awful. I ws wondering if anyone had an idea of what might have caused this.

At the service they did an oil change, cambelt and water pump change, front discs and pads, front caliper (it bound on the way to the dealer killing the disc!), rear shocks, and I changed the air filter, rear discs and pads berfore the service.

So far I've checked that the rear brakes are not dragging, the front discs are not dragging, that the camshaft pulleys are correctly alligned (appears OK froma visual check) and I've changed the oil for 5W-30 Castrol Edge incase they put the wrong stuff in it.

On a long motorway run the fuel economy is OK, in fact I got 60 mpg on a 400 mile round trip the other week. But under 'normal' acceleration the fuel economy drops like a stone, instantaneous mpg is dropping to single figures whereas before it would be in the mid 30's. On a short trip (10 miles) I'm lucky to break 40 mpg, before it would easily give mid 50's driving in the same style. It seems to pull OK, no more spoke

I'm tempted to go back to the dealer and ask them to run the software checks but I am affraid that I'm pouring money away chasing rabbits down holes.

I've read threads which mention coolant temperature sensor faults and Mass Air Flow sensor faults and fuel filter problems (changed about 40k ago), which I could change but it just seems odd that it all started post service!

Any advice greatefully received.

Dunc

Sounds like a timing issue.

The cam pulley has to be loosened when the belt is changed. The bolts that hold the pulley onto the end of the cam sit in slots that allow the pulley to be rotated on the end of the cam to change the timing. If it's off when the bolts are nipped back up again, that will affect MPG.

A visual inspection isn't good enough for anything other than a 'get you going' engine start. VCDS is needed to check, and if necessary, to re-set the cam timing accurately - on the TDI this controls directly both fuel injection & valve lifting.

No doubt, when asked, the garage will say that they did this.

Tell the dealer that you are not satisfied with their work, and that you intend to take it to an independent VAG specialist for a 'second opinion'. Get a diagnostics print-out. If the cam is off, the service wasn't done too long ago and the original dealer sufficiently cooperative, you ought to be able to recoup the cost of the check, and they should fix it for free.

Thanks, skodacarman. I've a big run coming up this weekend and will take it in after that. They're normally quite helpful at the dealer I use.

A 500 mile round trip this weekend with the family and I really struggled to get 50 mpg whereas normally it would easily have done 60 mpg on that same route with the same load! Definitely an on-load issue as I'm sure that the torque is down also.

I called the dealer today and they've booked me in for the 5th of Dec to run some checks, they'll look at the work they've done and not charge for that but will charge if it's not connected to the work they've done which is fair enough. They tried to fob me off a bit saying that if it was the cam timing that a warning light would have come on, I suppose it depends on how sensitive the fine tuning of the cams are to emmisions. All I'm certain of is that I can't go on haemoraging fuel.

I'll see what the dealer says and if it is not definitive then I'm taking it to an independant. Anyone know of an independant skoda expert in the Oxford area?

I would say its most likely a temperature issue, the colder it gets the more fuel you will use. The service is just now on your mind as a contributary factor when in fact its probably not that. My guess is temp.

I'd say timing too.

My timing was adjusted in an effort to cure a cold starting issue which adversely affected my MPG - no warning lights either, before or after.

I've had the car for 4 years and run it in much colder conditions than we've had since September when it was serviced. It's been low mpg since and I've been running it in various conditions to see what does and does not affect it. Cold weather shouldn't come into it on a long run as the engine is at temperature, if anything cold air is more dense and so the charge of air should contain more oxygen and thus more power. Remember on a cruise with low throttle use it's OK.

I've had the car for 4 years and run it in much colder conditions than we've had since September when it was serviced. It's been low mpg since and I've been running it in various conditions to see what does and does not affect it. Cold weather shouldn't come into it on a long run as the engine is at temperature, if anything cold air is more dense and so the charge of air should contain more oxygen and thus more power. Remember on a cruise with low throttle use it's OK.

Ah ok just noticed its 55 plate and i thought you hadn't had the car very long. My re-evaluated guess then is the timing or the air filter may have partally colapsed in the airbox under full throttle. I had this and it was letting more air into the inlet manifold than normal when you give the car plenty of gas although driving slowly i could still return good mpg as the load wasn't enough to suck the air filter down. easy quick check although you should be able to feel it i could.

Sorry, I wasn't very clear.

It wasn't the colder conditions that affected my MPG it was the dealers attempts to fix a cold starting issue I had.

This lead them to 'adjust' the timing which then adversely affected my MPG.

I guess what I'm trying to say is that there is a chance after the cambelt change that the timing is out.

If the motorway mpg is good, then I'd suggest it's not an injection timing issue. There isn't much scope for cam timing in a diesel to be out without pistons meeting valves.

Could it be that your readout is just now more responsive?

Under full pedal in 6th gear my PD140 is drinking ~16 litres per 100km. This is about 6 km/l or 18mpg. Higher in lower gears If if previously wasn't reading that low under full acceleration, then I'd expect it was simply reading wrong.

Update

On a recent run down to Gatwick (90miles) I managed 63 mpg from a cold start so motorway cruising still excellent. I've since fitted my 195/65-15 winter wheels and tyres and it's been good on local runs too, no other changes - odd given the weather is much colder now although I have started using Millers Power Ecomax in the fuel again. Too many variables here!

I've had the car back with Skoda and they've checked over the cam timing, other recent service work, and ran a diagnostic check, all free of charge. The cam timing was fine. They have found a fault code on all 4 glow plugs which they say is odd as normally one or two will play up rather than all 4. Skoda say that this may be a connection issue. The car starts fine so I've agreed to leave any further investigattion work until it becomes a problem and continue to monitor the mpg as it seems OK for now. The only thing they can think that the glow plugs would affect the mpg is on start up and whilst the engine is cold to pre-heat the fuel whilst it's running. They've quoted £135 for looking at the glow plugs and £240 (including the £135) if I want to change them but reccommend that they are checked first, not too bad I think.

With some heavy load long runs coming up over Christmas I'll be interested to see how it performs.

The only other thing that I had not mentioned before, but did mention to the dealer, is that I had to change the battery as it went flat after a light was left on (not the first time!) and I was wondering whether the ECU needed to relearn fueling parameters.

I've been assurred that the faulty glow plugs wont cause the DPF to clog, especially as I tend to mostly do long runs.

Dunc

1, you are now running winter wheel and your economy is up, did you have any new tyres fitted at or around the time of the service on the sumer wheels?

2, are you sure you have a DPF fitted? as BKD's don't have them. but if you do have a DPF the glow plugs have to work for regens to get the temps up

3, faults on all 4 golw plugs will be a wiring fault and its the same lume/wiring on the injetors

40k on the fuel filter!

I would get that changed for a genuine replacement, doesnt the manual say like every 20k miles

Glow plugs cost about £30 for a full set, the injector loom is about £80, and another 30 labour or so should get them all fitted. If you have a fault code on all 4 I would get them replaced along with the loom.

...but if you do have a DPF the glow plugs have to work for regens to get the temps up

Are you sure?

I'd read that the DPF increases in temperature from the injecting of additional fuel, nothing to do with the glowplugs?