Audi A4 B6 1.9 TDi poor fuel economy !

[Stefan Paiu]

Hi everyone,

I have just joined this forum and I am hoping someone can give me some clues as to where to find the solution to my problem.

I am getting very poor fuel economy on my 2003 Audi A4 1.9 Tdi (5 gears manual, 101 BHP, no modifications to it). I am getting an average of 25-30 MPG urban (Birmingham) and this if I drive it as economically as possible. On motorways it goes to about 45 MPG. I know this car should do 40 MPG without any problems in the city so there's got to be a problem somewhere. I have already removed the MAF sensor and cleaned with no luck. There is no loss in power as the car pulls really well.

I was hoping that maybe someone in Birmingham can help me hook it up to VAG com and see it there's any errors showing. Also, it's probably unrelated but who knows, the ESP module keeps coming on at random times and wouldn't go off until I turn the engine off.

Any advice would be greatly appreciated.

Thanks,
Stefan

[pdlh]

Hi Stefan,

I've no idea if this helps, and I have the 130 BHP version 5 speed, on a 52 reg, so slightly different setup but for the past 2 years I've suffered bad fuel consumption, I had it serviced, no difference? was only doing 485 miles on a full tank of fuel, compared to the original 650 it used to consistently do. No faults appeared on VCDS scans, engine all running fine?

Only thing I noticed was it burned out a set of front brake pads in about a year 8 - 10k miles. The garage said the front caliper had stuck on, great cost for a new caliper, pads and discs. Even after it was done, I thought the front left side always ran hotter than the right. 9 months later, another set of brake pads burned out only on the front left. This time garage replaced brake master cylinder and servo. Overnight difference, Fuel economy back to 600 plus miles on a tank of fuel.

Garage said the brake master fault was quite common on the 2002 - 2003 age cars.

Not sure if it's the same problem on your car, but might be worth seeing if your front left wheel is hot?

The only thing that makes no sense, is why all the brakes did not stick, I don't know why it only affected the front left?

Paul

[Stefan Paiu]

Hi Paul,

Thanks very much for your reply. I took the car for a ride today but didn't notice anything wrong with the brakes. When I bought the car in August it was shaking when braking from over 60 mph. It was due to the front brake discs being warped but I had them changed and the mechanic didn't notice anything else unusual.

What I also noticed recently is that the water temperature doesn't rise to 90c. I drove around 10 miles and the temperature went to 70c, without having the heating on. Could this lead to the car doing 25 mpg instead of 40? It seems like a huge difference. Nonetheless, is it worth changing the thermostat? This is my first diesel car so I don't really know how long it should take to warm up.

Thanks,
Stefan

[arman123]

If the car not getting up to temp 90 and staying there then your state could be stuck open overcooling engine hence crap mpg change the state for a genuine one and the coolant temp sensor when you get the state changed make you tell them to check the state housing that the lugs that hold the stat in have not been damaged the stat twist in the housing and locks in place with the gasket coolant temp sensor is a bit of a tight job just at bottom of bulkhead make sure you get genuine one and the gasket that goes with it and the clip that hold it in place clip is very easy to break do buy two change these items and your mpg should improve a lot

[niall campbell]

you could also blast the exhaust out to de-coke it. Just stay in 2nd gear and run along the road with the revs just under the red. Watch all the black crap coming out your exhaust.

[Stefan Paiu]

I've tried blasting the exhaust as niall suggested and it seems to have helped a little bit. On a 10 mile journey with almost no traffic I managed 32MPG this morning but didn't let the engine go past 2000RPM. The temperature still doesn't get past 70c but the mechanic I usually go to is on holiday for 3 weeks and I have to wait until he comes back. I also asked someone another mechanic about the temperature and he said that as long as it gets to 70c it is fine, as some cars run cold. What I have also noticed is that the mpg drops radically when the car is not moving or when it's not in gear which i know it's normal but still it seems too much.
I don't know if it's relevant or abnormal but when in first gear with very little or no acceleration the computer shows 10-15MPG.
I would change the thermostat myself but I've read that you spill about 1-2 litre of coolant and I don't want to spill it al over the road where I live as I don't think it would make my neighbours happy:).

Any other thoughts? Or any good mechanic in Birmingham that could have a look?

Thanks,
Stefan

[arman123]

Frontier Volks Works 52 Cherrywood Rd, Birmingham, B9 4UD 0121-773 9396
try these guys really good

[niall campbell]

why don't you let engine go above 2000 rpm ? Having a turbo in a diesel car helps the fuel economy and by using low revs , it may not be kicking in . You could try using an additive in the diesel fuel as well. In my A 6 I am getting 44 mpg at ten mile point when going to work , however I start really early and hardly meet another car. My car has just opened up at 40,000 miles and on the motorway I am getting 62.3 mpg at 50 mph. I would also look at your air filter and diesel filter to be changed before spending money in a garage. Don't be worried about a diesel car sounding noisy and changing up gear , just don't let it get so high you are thrashing it ! You will still be saving money compared to a petrol car

[Stefan Paiu]

why don't you let engine go above 2000 rpm ? Having a turbo in a diesel car helps the fuel economy and by using low revs , it may not be kicking in . You could try using an additive in the diesel fuel as well. In my A 6 I am getting 44 mpg at ten mile point when going to work , however I start really early and hardly meet another car. My car has just opened up at 40,000 miles and on the motorway I am getting 62.3 mpg at 50 mph. I would also look at your air filter and diesel filter to be changed before spending money in a garage. Don't be worried about a diesel car sounding noisy and changing up gear , just don't let it get so high you are thrashing it ! You will still be saving money compared to a petrol car


I don't let the engine go over 2000 RPM because I noticed that the consumption tends to be lower if I do so. If I change gear at 2500 for example I get around 22 MPG compared to 26-27 if I change at 2000. I will get my filters changed this week and see if it helps.

[niall campbell]

Changing the diesel filter is a must coming up to winter. If theres any water in it , it will freeze. That's the problem with putting cars in for a service , trusting that ALL filters are changed. Keep us posted !

[Stefan Paiu]

Hi,

Sorry I didn't reply earlier, but due to work and uni I just managed to leave the car at a garage a couple of weeks ago for cam belt and filters replacement. I bought the car in september and the mechanic told me the filters haven't been changed in a really long time and that I should see improvements right away. I have also asked him to run a vcds and he said that he's only found one issue, the braking light switch. He also recommended to change the MAF and possibly thermostat and temperature sensor if there are still problems. At the moment I am able to see improvements but I'm not sure if it's because of the filters or the additive that I've been putting in the diesel. So I'm able to get to 40 MPG in about 3 miles but doing 40 MPH and over, on 4th gear. Normally I get about 27-30 MPG which still seems a bit low for this car.

So would you think it's worth changing the MAF sensor and the temperature one given that nothing unusual showed on VCDS? Also, as I said before, the computer shows a drastic increase in medium consumption (around 0.2 MPG drop per second) when I am stopped at traffic lights.

[Alfonzo]

Hi Stefan,

I too am having trouble with my MPG although not as bad as yours perhaps. Just to want to talk about MPG; obviously if you have the engine running but are stationary (say at traffic lights) your MPG is zero. You are getting no miles per gallon. If you are crawling along at slow speed you will get a pretty crappy MPG. If you have the car flat out at 130mph you will get a crappy MPG. Between these extremes you will get the optimum fuel economy (usually around 55mph for best economy but varies from car to car). I only mention this to make sure you've understood the figures you're getting, I don't mean it to sound patronising :D. It's acceleration that kills MPG, so generally speaking keeping the revs down is good. I don't agree that having the turbo 'kick in' will help with MPG. That's the basics.

I wouldn't change your MAF sensor. I would look at the thermostat & temperature sensor and get those changed. This is what I need to do on mine too. It appears that both fail and that if the thermostat is failing the engine will be colder than it is designed to be, and the ecu will deliver more fuel. If the sensor fails, the ECU will think the engine is colder than it actually is and will over fuel. Both situations will lead to poorer MPG. I don't think the mechanic who said 70 deg c is ok is right. I'm 99% sure these engines need to be at something like 87 deg +

Obviously the cold weather we have at the moment will reduce all cars MPG, regardless of whether they have a problem or not, but if your thermostat is dodgy the decrease in MPG will seem even worse.

[Stefan Paiu]

Hi Alfonzo,

Thanks a lot for your reply.
Do you think it's worth changing both the thermostat and temp sensor at the same time? Or try with the thermostat, which is cheaper, and if there's still a problem, move on to the sensor?

Thanks,
Stefan

[Doctle Odd]

The car may have an aftermarket CTS that is overfueling the car but it wouldn't necessarily show a fault code. A thermostat and genuine CTS sensor would be my next step, do the thermostat first and if the car doesn't hit 90 degrees in 5 miles its the sensor. No cars are supposed to "run cold"

[Stefan Paiu]

So after stupidly wasting about 5 hours, I've managed to remove the CTS to see the part number. I've been looking for the sensor in the wrong place and ended up removing a sensor that looked exactly the same but was connected to a pipe leading to the diesel filter. That one was really hard to put back on and I might have damaged it. I'm not sure what it does but I'm afraid it might also be leaking diesel now.
Moving on to the CTS, after removing it I noticed that the O ring was dilated and I'm quite sure it doesn't seal properly anymore, as I took the car for a 5 mile drive after topping up about half litre of coolant, and noticed that the level had dropped with about half a litre again. Could it be because it pulled it into the system as I was driving?
I've ordered new CTS and thermostat and I will change both on Monday, but I'm not sure if I can drive the car until then as I am afraid that it could be leaking diesel or coolant.
Also, does anyone know what that diesel sensor does and if I should change that too after messing with it?

[Doctle Odd]

Can you post a photograph of it?

[Stefan Paiu]

So No 1 (right) is where the sensor from the diesel filter is and No 2 (left) is the coolant temperature sensor.

19458


And below is a photo from the left side of the car. You can see the diesel sensor behind the fuel filter.

19459

[Doctle Odd]

Is it leaking fuel? Mzybe a new seal would fix it. Make sure the CTS is pushed in securely and the clip is on properly

[Google44]

If you had CTS out you will have to refill coolant after a bit of a drive. Expect to add about 2L of coolant after CTS has be out.

[pauldazzle]

The 2 pin sensor you removed is the fuel temp sensor. It has an o ring & c clip the same as the CTS. If it's leaking you probably haven't got it seated correctly or the o ring is goosed.

[Morgaine]

Did changing the stat help with the problem? I have noticed with my A6 2.5 TDI quattro that it's doing somewhere in the region of 20mpg and that it runs very cold. The temperature barely moves unless I'm sat in traffic. I've not had it very long and had other things to fix (ABS ECU and a fuel leak!) which took priority but now looking at the fuel consumption. Given the low running temperature it sounds as if the thermostat could definitely be the culprit?

[Google44]

When I changed mine it did improve consumption. However, still not brilliant. I've had so far bottle of Redex in and tried another MAF. None seems to improve it. Get about 42 on motorway. If you look on my other thread I am seeking advice on how to diagnose the fault (if any) using VCDS.

[Stefan Paiu]

I've changed both the CTS and thermostat on friday. Now it gets to 90 deg C in about 10 mins. The fuel economy is still not great but there's only 5 miles to work so I didn't really have a chance to test it properly. I've driven today in quite heavy traffic and I got about 27 MPG, which still seems low.
Now my problem is that I've put about 3 litres of coolant and I've looked today and it's dropped about half centimetre again. I suspect it's either leaking from the thermostat or the system needed a bit more. Another problem is that it gets really hot inside the car and I've noticed today that the passenger side blows hot air even if i set it on low. Driver side is fine, although it still seems warmer than before.

Bottom line, I've changed the CTS and thermostat so the temp stays to 90c, but still no great effect. What's next, MAF sensor?

[kite]

If your heater blows hot when set to cold you may have an air flap motor not working correctly.
Scan the car for faults.

I wish I could tpye...

[red40red]

hi, I've been having the same problem. I've read that the camshafts wear and thats the cause. Sorry it's bad news, but hopefully it's just a sensor (for both of us!).

[Alfonzo]

Camshaft wear? That's interesting. Are there any other tell tale signs or ways of determining if they are worn excessively?

[adamss24]

Yyou need to take the rocker cover off and inspect the cam lobes for wear, there are hundreds of pictures of worn cams on line...

[Alfonzo]

Yyou need to take the rocker cover off and inspect the cam lobes for wear, there are hundreds of pictures of worn cams on line...

Cheers. Hundreds of pictures eh? Ha Ha! That's never encouraging ;)

[Autobulbs]

There seems to be a lot of really bad ideas about low low rpm giving good fuel, you need to drive to the torque curve of the car with gentle acceleration. Driving at extremely low RPM strains the engine and will be adding more fuel than gentle acceleration with the torque curve of the car. Straining the engine will also 'coke' it up quicker and it leads me to believe you may have a few minor problems dropping your MPG. A good french tune up once and a while is good for your car (full throttle high revs) Check your filters are clear as said, has your oil been changed? And a serious one check your tyre pressures are all correct and your alignment is also correct these are very important.

Let us know how it goes.

[Doctle Odd]

Can I suggest a pint of petrol to half a tank or so once a month. All the stuff below is true give her some clog every so often it's fun :)
There seems to be a lot of really bad ideas about low low rpm giving good fuel, you need to drive to the torque curve of the car with gentle acceleration. Driving at extremely low RPM strains the engine and will be adding more fuel than gentle acceleration with the torque curve of the car. Straining the engine will also 'coke' it up quicker and it leads me to believe you may have a few minor problems dropping your MPG. A good french tune up once and a while is good for your car (full throttle high revs) Check your filters are clear as said, has your oil been changed? And a serious one check your tyre pressures are all correct and your alignment is also correct these are very important.

Let us know how it goes.

[Alfonzo]

I'm good with the idea of adding a bit of petrol or reddex or whatever, except I'm sure I read somewhere that with the PD engines you are advised to add nothing at all. Something to do with the injectors I thought..

[Eshrules]

Millers fuel additive if you're able to afford better than redex.

BTW - A/B - it's Italian tune up, let's not give those horse eating folk credit for stuff they've not done ;)

Italian tuneup - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Italian_tuneup)

[Alfonzo]

Millers is OK with PD engines?

[Eshrules]

Millers is OK with PD engines?

It was with both of mine and I'm pretty sure devonutopia uses it in his furby.

Don't add anything if you're that worried, take it for a good stretch once a month and that'll help to keep it clear.

Sent from my Nexus 7 using Tapatalk 2

[red40red]

if it's just light wear, you'd hardly notice apart from fuel economy. It's easy to take of cam cover and have a look. Take about an hour. google image a worn cam and see if yours looks the same. Mine does :( checked it today. it's worth checking as it only gets worse and more expensive. good 2nd hand cam and lifters about £200. I'll let you know how I get on. good luck.

[Burhaan]

Hi. I am new on this forum as well. an i dea is to check the condition of the air cleaner element as well and fuel filters. I dont quite no how to add a post here so ia am hoping u can help me. I have an old Audi 1.8 1997 model Auto. The transmission is fairly aggressive wen changing to 2nd gear and downchanges as well. It knocks very hard when changing down to from 2nd to 1st. Any advise?

[Doctle Odd]

I'd start by changing the transmission fluid

[Alfonzo]

I'd start with a new thread :D

[Stefan Paiu]

Hi everyone,

So after changing the thermostat and coolant sensor, the temp goes up to 90 in about 20 mins which is good. However, it still feels a lot hotter inside the car, even if the climate control is set to 20 deg C. This only happens at random times, so I guess I'll check the motors controlling the flaps. Moving on to fuel consumption, 30 pounds worth of diesel (20 litres) lasted me 140 miles, with moderate to clear traffic and economic driving. After my calculations, it's approx 32MPG, which still seems a bit low. Assuming it is not the camshaft, as someone said above, shall I change the MAF sensor?

Thanks,
Stefan

[Alfonzo]

32 MPG is definitely not right, unless you drive it like an **** :D. And assuming you don't - then something ain't right. Should be at least 40mpg. I changed my thermostat recently as it wasn't getting to temp. The new one is much better, however no significant improvement in MPG really.

[Stefan Paiu]

yeah, I don't drive it hard at all. However, I'm interested to know if there are any members around Birmingham with a model like mine ( A4, 1.9TDI, 2003, manual, 100Bhp) and what consumption do they get around town.

[HalfAudio]

Listen, I drive such engine for 5 years and i got 211000 miles on it. i have done 100000 miles since i bought it. 50mpg urban and 40-45 mpg city it all depends from weather,road condition and understanding your cars soul (engine) Since i bought it i have just trashed it till red line whit nearly every gear. I had my turbo off, inlet manifold and exhaust manifold, how do you think was it clogged whit carbon deposits or anything else ? NO! just cleaned turbo a bit so it doesn't stick (just in case) and that's it. If you want your diesel to last then don't drive like a granny. It is healthy to shift after 2000rpm otherwise you will spoil your engine including inlet manifold and EGR. And dont listen in to the bulls**t that turning radio and air con off will save your fuel. At least it doesn't happen whit this engine and car. Driving in city mainly on 4th gear you don't need to **** in 5th gear.

1Clean your EGR if its clogged up

2Change filters and oil every 8 months or so (use same oil don't switch brands and viscosity) Genuine vw oil costs 30 quid per 5l and that all you need don't buy long lasting oil. DON'T EVER LET IT DROP LOW other vise you will end up filling it up every now and then. Learned from my mistake a year a go...

3When you change your cam belt make sure you change your thermostat, water pump and if you just bought it just for the sake change cooling sensor as well. If you loose coolant check your coolant servo as it may have a crack underneath it (you might not even notice it until you have removed it. AND if engine temperature is low try to use more water and less coolant concentrate. Speaking about this make sure there is no water in battery area!!! cant stress it enough.. clean your drain holes other wise you will end up whit faulty servo. DOnt forget to change the brake fluid and same goes for clutch pedal as they share the same fluid.
AND if you ever get a braking problem and they are not calipers worn/damaged brake rotors/pads or worn flex i brake pipes then first try to check vacuum hoses as they can be damaged or even collapse inside.

4Check that tyres are good and pressure is ok might help whit alignment adjustment (not just check as most garages do) they just rob u for printing a paper sheet and wiggling the car a bit.

5Check and clean all the ground points for battery and engine.

6And finally make sure you have no boost leak or fuel leak this can impact not only four overall performance but mpg as well
There i a quite common thing for a Tandem/Vacuum pump to leak a good new set of rubber and steel gasket will fix this and for better vacuum you can put new rubber hoses and clamps.

7Don't use KN performance air filter as it can and probably will in time kill your mass air flow sensor.

I hope this helps and you have a healthy engine.