Lost between 5-10mpg - TDI 90 (ALH)

[octaviadan]

Hi there:)

Wondering whether somebody can help me with this. I have been noticing a gradual increase in fuel consumption from my 2001 Ambiente TDI (90) hatch over the past few months:(.

My daily commute is 35 miles each way and would consistently give between 60-65mpg no problem. I had even achieved 70-71mpg on a couple of occasions on the same journey! Also on a run (for example to the east coast) would achieve 67-68mpg.

Anyway, since around August this has gradually dropped to 55-58mpg (58 being the absolute best) on my daily commute, and on a recent trip to the east coast 'only' produced 57mpg.

There has also been a drop in performance.

My Octy has done 123k and I had the full cambelt/tensioners/rollers/waterpump replaced at 121k by a good friend who knows VAG TDI cars really well. Timing was set up using VAG COM. I also subsequently changed the MAF sensor from the original, new fuel filter (and used a fuel system cleaner when changed), new air filter and oil and filter change (engine was also flushed at this change).

I have had the codes read a few times with VAG COM but always comes back clear. I have also had 'live' data read through VAG COM to see if the new MAF was faulty but this is working as it should.

I have also noticed that my Octy also appears to have lost the ability to 'creep' in second gear in slow moving traffic (10-15mph) with no throttle. Almost stalls when I try to do this now.

It certainly doesn't feel right anymore :(

Any ideas anyone??

Thanx

Dan

[eddies]

Not sure if this is your problem.......on my 110 Tdi I noticed it was using more DERV than normal. I replaced the 4-pin temperature sensor on teh back of the engine and the milage has improved since then. I suspect the cold start valve was getting a signal from the sensor and adding more diesel - hence the lower milage. the part is cheap £16 from GSF or others. There are two types of connector 1) a D-Shaped plug, or 2) a Square-shaped plug. Check before you buy so you get the right part.

[octaviadan]

Not sure if this is your problem.......on my 110 Tdi I noticed it was using more DERV than normal. I replaced the 4-pin temperature sensor on teh back of the engine and the milage has improved since then. I suspect the cold start valve was getting a signal from the sensor and adding more diesel - hence the lower milage. the part is cheap £16 from GSF or others. There are two types of connector 1) a D-Shaped plug, or 2) a Square-shaped plug. Check before you buy so you get the right part.

Thanks for this. Is this the sensor which also controls the temperature gauge? If it is then this has also been replaced about six months ago as my gauge kept dropping back to zero. How did you find your fault? Was it by reading the codes?

I am wondering now whether my trip computer had been reading over optimistically as I have been reading other threads and 55-57mpg for a 90 TDI seems normal!! I have never checked the accuracy of the trip computer so I will try some manual checks. I have noticed a drop in performance though.

[Allams Skoda]

Does it feel sluggish or reluctant to rev above a certain amount of RPM?

[cheezemonkhai]

If you have a new air filter in and you have not had a new MAF in the last 60kish miles I'd be looking and a new MAF at a cost of about £65.

Fitting is easy as long as you have a screwdriver set and a set of mole grips to open a spring clamp.

[octaviadan]

Does it feel sluggish or reluctant to rev above a certain amount of RPM?

Yes, does feel sluggish and feels as though something is holding back but does rev all the way round to the red line when limiter kicks in.

[octaviadan]

If you have a new air filter in and you have not had a new MAF in the last 60kish miles I'd be looking and a new MAF at a cost of about £65.

Fitting is easy as long as you have a screwdriver set and a set of mole grips to open a spring clamp.

I have fitted a new (genuine) MAF about three weeks ago, which replaced the original one fitted from new. I had this tested against 'live' data on VAG-COM as I thought it may have been faulty but is working fine.

I even swapped the new MAF back to the old one to test and there was only a very slight difference noted between the old and new one (the new being slightly better).

Very puzzling as I thought that a new MAF would cure the problem!!!:(:(

[iain]

might be nothing but have you recenlty change brands of fuel eg started buying supermarket fuel instead of one of the oil companies?

only asking as I have had in the past where when you stick a few tanks of the cheap stuff in that the economy goes down, the car does not feel quite as responsive.

prehapse try sticking a couple of tanks of the good stuff in and see how it feels.

[AndrewTait]

Could the clutch be slipping??? As the friction surface degrades, it will start to slip, and as such the engine will need to turn faster to get the same level of speed at the wheels.

This would also explain the lack of performance, and also the lack of creep.

[Railroad]

Could the clutch be slipping??? As the friction surface degrades, it will start to slip, and as such the engine will need to turn faster to get the same level of speed at the wheels.

This would also explain the lack of performance, and also the lack of creep.

If the clutch was slipping it should be immediately obvious to anyone......

[athol]

Thanks for this. Is this the sensor which also controls the temperature gauge? If it is then this has also been replaced about six months ago as my gauge kept dropping back to zero. How did you find your fault? Was it by reading the codes?

I am wondering now whether my trip computer had been reading over optimistically as I have been reading other threads and 55-57mpg for a 90 TDI seems normal!! I have never checked the accuracy of the trip computer so I will try some manual checks. I have noticed a drop in performance though.

My trip tells me I'm often getting 65mpg + even up to 72mpg once, but true mpg filling brim to brim is 55-57mpg so I'd say its about normal.

[eddies]

The temp sender unit did not show up on VAG when i scanned it but I replaced it anyway as it is easy to do and not expensive. When I scanned after replacement it did show Open or Fault to Earth for the sender unit so I cleared the codes and re-scanned. All fine since then.

[Allams Skoda]

It sounds like a faulty air mass meter to me, but it's worth noting I'm not a mechanic just a salesman so I'm probably wrong but that is what it sounds like, or perhaps it's a very, very restrictive airfilter you've fitted?

[octaviadan]

It sounds like a faulty air mass meter to me, but it's worth noting I'm not a mechanic just a salesman so I'm probably wrong but that is what it sounds like, or perhaps it's a very, very restrictive airfilter you've fitted?

I have had the new MAF tested via VAG COM using live data as I did think that the new MAF was faulty. At the same time I also swapped out to the original MAF which was also tested at the same time and this actually indicated that it was still operating within limits.

When I changed the MAF I was amazed how black the air filter was - even though this was changed only 10k previously, and cause I needed one quick, I just went and bought an own brand air filter from my local Halfords (cost £13.99 though!!)

[octaviadan]

The temp sender unit did not show up on VAG when i scanned it but I replaced it anyway as it is easy to do and not expensive. When I scanned after replacement it did show Open or Fault to Earth for the sender unit so I cleared the codes and re-scanned. All fine since then.

If this is the sensor which controls the temperature gauge on the dash, this has been replaced for a new later 'green' one.

Is there another separate temp sensor which controls the ECU? Where abouts is it as I will replace if only £16!

[mbames]

I think the one temperature sender does both the ECU and the dash gauge.

[eddies]

The one sender unit does BOTH the dash guage and the ECU.....................

[octaviadan]

Could the problems I am experiencing be down to the EGR system needing a good clean???

[octaviadan]

Cleaned EGR valve out over the weekend - was covered in thick black soot!!!! Ought to have done the inlet manifold but didn't have the confidence to remove this....

Anyway, seems to run a bit better than before but still no improvement in fuel economy..:thumbdwn:

Would a rolling road diagnostic/tune be beneficial as there is a place just up the road from me who is good but is this something that can be done only on petrol vehicles??

Any other ideas/suggestions would be greatly received!!

Many thanks

Dan

[thephm]

it could be the added anti waxing agent they add to the fuel in the winter months - My fuel economy has dropped by 5-10 mpg for the last 2 tank fulls.

[greg123]

Dan,

Nice to see someone local on the board.

Check the case pressure relief valve on the VP37 pump, they fall apart and need pressing together - prevents proper advance being reached.

Also on the vag-com timing graph, make sure static timing is set to 70/110.

Take a look at the amount of bubbles in the clear fuel line, there should be little or none.

Re the temp sender, it should be a green one. If it's black, replace it with the newer 059919501A version.

Make sure your tyres are all at least 30psi.

If you can send a screen shot/info on the static timing from the tdi timing graph on vag-com and also a log or print screen of requested vs actual boost levels that would be good. VNT or operating mech starting to fail can also cause a drop in mpg/performance.

A rolling road really isn't the way to go I feel, you already know it's down on performance and those rollers can't tell you much else.

Greg.

Hi there:)

Wondering whether somebody can help me with this. I have been noticing a gradual increase in fuel consumption from my 2001 Ambiente TDI (90) hatch over the past few months:(.

My daily commute is 35 miles each way and would consistently give between 60-65mpg no problem. I had even achieved 70-71mpg on a couple of occasions on the same journey! Also on a run (for example to the east coast) would achieve 67-68mpg.

Anyway, since around August this has gradually dropped to 55-58mpg (58 being the absolute best) on my daily commute, and on a recent trip to the east coast 'only' produced 57mpg.

There has also been a drop in performance.

My Octy has done 123k and I had the full cambelt/tensioners/rollers/waterpump replaced at 121k by a good friend who knows VAG TDI cars really well. Timing was set up using VAG COM. I also subsequently changed the MAF sensor from the original, new fuel filter (and used a fuel system cleaner when changed), new air filter and oil and filter change (engine was also flushed at this change).

I have had the codes read a few times with VAG COM but always comes back clear. I have also had 'live' data read through VAG COM to see if the new MAF was faulty but this is working as it should.

I have also noticed that my Octy also appears to have lost the ability to 'creep' in second gear in slow moving traffic (10-15mph) with no throttle. Almost stalls when I try to do this now.

It certainly doesn't feel right anymore :(

Any ideas anyone??

Thanx

Dan

[KenONeill]

I've "lost" about 5mpg as usual over the last 2 tanks or so, and I know it's not a running problem since the car's just been serviced.

As Greg says, all a rolling road will tell is what you already know.

[octaviadan]

Dan,

Nice to see someone local on the board.

Check the case pressure relief valve on the VP37 pump, they fall apart and need pressing together - prevents proper advance being reached.

Also on the vag-com timing graph, make sure static timing is set to 70/110.

Take a look at the amount of bubbles in the clear fuel line, there should be little or none.

Re the temp sender, it should be a green one. If it's black, replace it with the newer 059919501A version.

Make sure your tyres are all at least 30psi.

If you can send a screen shot/info on the static timing from the tdi timing graph on vag-com and also a log or print screen of requested vs actual boost levels that would be good. VNT or operating mech starting to fail can also cause a drop in mpg/performance.

A rolling road really isn't the way to go I feel, you already know it's down on performance and those rollers can't tell you much else.

Greg.

Hi Greg

Thanks for this. Unfortunately my mate with VAG-COM is out of action at the moment due to a slipped disc so unable to get some screen shots from VAG-COM.

Fuel lines look fine - no bubbles.

Temp sensor is the new green one.

Tyre pressures checked every week (have to top up to 5psi on two wheels).

Anyway I see that you are in Nottingham (off J26 M1). I work in Nottingham (West Bridgford) so just wondering whether you could possibly have a look at it for me???

Many thanks

Dan

[athol]

I've "lost" about 5mpg as usual over the last 2 tanks or so, and I know it's not a running problem since the car's just been serviced.

As Greg says, all a rolling road will tell is what you already know.

Noticed my car has also dropped 3-5mpg last couple weeks, but getting due for a service in next 2000miles, plus it could be the anit waxing agents in the fuel as someone already said.

[greg123]

Hi Dan,

I'm sure I can help. Drop me a PM message and I'll give you my email address.

Cheers, Greg.

Hi Greg

Thanks for this. Unfortunately my mate with VAG-COM is out of action at the moment due to a slipped disc so unable to get some screen shots from VAG-COM.

Fuel lines look fine - no bubbles.

Temp sensor is the new green one.

Tyre pressures checked every week (have to top up to 5psi on two wheels).

Anyway I see that you are in Nottingham (off J26 M1). I work in Nottingham (West Bridgford) so just wondering whether you could possibly have a look at it for me???

Many thanks

Dan