TDI fuel consumption diagnosing

[Google44]

Hi


I've got A4 sport Avant 1.9 TDI. At the moment it is very bad on fuel getting less then 40 mpg on motorway doing 70-80. I cannot fault how it drives of pulls.

I was going to try using VCDS to find out what is faulty but not sure where to start. There is a few 'block measurement' you can do. I wonder if somebody can advice what to look for and how to measure it.


So far I've checked coolant temp and it is 90 C as on dash. It had faulty CTS where it was showing 90 on dash but 65 to ECU. It was changed over weekend. Maybe I need to disconnect the battery so ECU can start to learn again.


Any advice welcomed.

[Eshrules]

Hi


I've got A4 sport Avant 1.9 TDI. At the moment it is very bad on fuel getting less then 40 mpg on motorway doing 70-80. I cannot fault how it drives of pulls.

I was going to try using VCDS to find out what is faulty but not sure where to start. There is a few 'block measurement' you can do. I wonder if somebody can advice what to look for and how to measure it.


So far I've checked coolant temp and it is 90 C as on dash. It had faulty CTS where it was showing 90 on dash but 65 to ECU. It was changed over weekend. Maybe I need to disconnect the battery so ECU can start to learn again.


Any advice welcomed.

You'll need to lower your average speed if you want to increase economy.

[Google44]

Sorry, when I say 70-80 this is not average. It means I was doing between 60-80 on speedo which means about 55-75 in real speed.

Anyway, doing 75 mph at 38-39 mpg - does that sound about right for AWX 130 engine ? I was under impression at 60 mph they should do 50-60 mpg.

[Doctle Odd]

She does seem a little hard to run but some of it could be down to driving style. The high MPG is usually done by smooth acceleration, gear changes at the correct time, staying within the speed limits and no red lining it! A VCDS scan is the place to start

[Eshrules]

Sorry, when I say 70-80 this is not average. It means I was doing between 60-80 on speedo which means about 55-75 in real speed.

Anyway, doing 75 mph at 38-39 mpg - does that sound about right for AWX 130 engine ? I was under impression at 60 mph they should do 50-60 mpg.

I never once saw 60mpg out of my 130, but sitting at 55/60 (on the speedo, not guessed speed) will offer the highest economy, coupled with the tips odd's given you above.

Getting MPG out of a car is more than picking the right engine unfortunately.

[Google44]

Thanks for replies. I guess all I am trying to get is to confirm that injectors, MAF etc is OK. Is there anywhere a short guide how to test these components using VCDS?

Also, my average I've claimed above was with a lot of neutral drive. I had B5 Avant before this and with the same style of driving I've got 68 mpg! Hence I've got 2003 Avant thinking it is not going to be far from it. Guess did not expect it to be half.

Just trying to make sure there is nothing wrong with the car. The VCDS shows no codes at all. I can measure MAF but not sure what is good reading.

[Alfonzo]

I'm in a very similar position to you Mr Google so be interested to hear what you discover and likewise will let you know what I find on mine. There's no damn way it should be 40mpg, although bear in mind the recent cold weather hurts economy quite a bit.

[Google44]

Yeah, she defo take more fuel then she should. No other fault at all. I have noticed that just a slight and slow press on gas pedal makes it go from 60 mpg to 20+. That should be visible on VCDS. I will try to do recording of MAF and injectors and post the log here.

Tried so far:

Cleaned EGR
Cleaned MAF
full service

[Sam]

I have noticed that just a slight and slow press on gas pedal makes it go from 60 mpg to 20+.

Are you sure you're not looking at your instantaneous MPG reading?

[Alfonzo]

I don't undersand why you didn't get an improvement once you replaced the faulty CTS? If it was telling the ECU the engine's at 65 then surely the engine would be over-fueling?

[Google44]

I do ....only to see the drop. However, the figures I've said before is average mpg. From full to 'No Fuel' LED on I get about 500 miles.

[rocker55]

I do ....only to see the drop. However, the figures I've said before is average mpg. From full to 'No Fuel' LED on I get about 500 miles.

I'm roughly around 540 miles on a 2002 A4 Avant 1.9 Tdi quattro sport with 170bhp remap. No silly accelerating and harsh braking though, so happy with that. Mostly motoway miles, well A9 so not much urban driving.

Not bad since it has 187K on the clock.

[ametlib]

I don't undersand why you didn't get an improvement once you replaced the faulty CTS? If it was telling the ECU the engine's at 65 then surely the engine would be over-fueling?

Overfuelling will make the car go faster, then you let off the throttle and hokus pokus, no overfuelling. What happens is, the ECU advances the timing ( due to the low temp reading) and actually improves the fuel economi !

[Col]

The MPG sounds about right based upon my experience. I'm on my 3rd AWX engined car and keep very detailed spreadsheets.

Passat 1 owned 2007-2009; 40mpg over 43k miles with an avg speed of 42mph
Audi A6 owned 2009-2010; 43mpg over 15k miles with an avg speed of 36mph
Passat 2 owned 2011-now; 43mpg over 23k miles with an avg speed of 35mph

I've omitted decimals for simplicity and the mpg figures are actual as filled, brim to brim. The average speed however is from the cars computer though.

In Passat 1, I put a lot of miles hooning up and down the motorway which reflects in the lower mpg figure. In the A6 and the current Passat, the journeys are far shorter and I travel at a far more relaxed pace.

Your car seems normal if you hoon along.

[Alfonzo]

That's good info BigCol, and based on those mileages covered very meaningful. I had hoped for better though - 50mpg was my goal, but possibly not to be!

[Alfonzo]

ametlib: Overfuelling will make the car go faster, then you let off the throttle and hokus pokus, no overfuelling. What happens is, the ECU advances the timing ( due to the low temp reading) and actually improves the fuel economi !

So, if the CTS is under-reading you might expect for better fuel economy?
If the thermostat is not closing properly and the engine is actually colder than it should be, you would expect the fuel economy to be worse though?

[Col]

It is easy to get stupidly high one off MPG and Range figures but in the real world low mid 40's is to be expected. If your doing a long run at a good low speed, 55-60mph with the lorries you can get some scary good figures.

I used to do and play a "range" game on here, there is a thread somewhere. I'd fill up after doing some hypermiling mpg speed so the ecu kept the range high, and whilst filling up vent the tank (search for this, but you can force another gallon of fuel into the tank). The best I got was with miles driven plus indicated range a tad over 1,000 miles on the tank. suffice to say most tank fulls were in the region of 600 miles on the A6 (bigger tank than the A4 & Passat)

http://img.photobucket.com/albums/v602/colin__/A6/Image071.jpg

As for temperature sensors, both the coolant and fuel temp sensors are important to efficient running.

If the car is new to you, I'd plan on doing both the coolant temp sensor and the thermostat whilst the coolant is drained down, they are both common failure items on these cars. But saying that yours might be (looks like it is) fine.

I've not had any bother with the fuel temp sensor.

[jreddy]

Hi guys sorry to jump on this thread but im in the same position with my 2007 A4 1.9TDI PD 115bhp with a remap, BRB engine and EGR delete software but havent blocked off the valve yet .My problem is low MPG also, around 38 mpg at every fill (fill drive till nearly empty then fill and calculate) was slightly less before remap .I only have the car for 5month's,but seems vpoor .I have connected VCDS and there are no codes stored ,also changed out map sensor from my wifes golf same part no .(No improvement in MPG but maybe slight power improvement) Also changed the usual oil,fuel,air filters car drives perfectly,but this is very annoying .The car as low milleage 63k miles,doesnt smoke and had 1 other carefull owner ,I mostly do short runs 7 miles to work and back ,But have done longer runs ,doesnt improve things much .Should I be getting much better MPG what are you guys getting .I posted in this section because its mostly 1.9tdi,s here .My hunch is the maf sensor or the thermostat but both were reading ok on VCDS ,thermostat was reading 1or 2 degs short of 90deg according to guy with VCDS,.
Thanks if you have managed to read this far ,and any thoughts ideas would be taken on board :)...

[Eshrules]

Hi guys sorry to jump on this thread but im in the same position with my 2007 A4 1.9TDI PD 115bhp with a remap, BRB engine and EGR delete software but havent blocked off the valve yet .My problem is low MPG also, around 38 mpg at every fill (fill drive till nearly empty then fill and calculate) was slightly less before remap .I only have the car for 5month's,but seems vpoor .I have connected VCDS and there are no codes stored ,also changed out map sensor from my wifes golf same part no .(No improvement in MPG but maybe slight power improvement) Also changed the usual oil,fuel,air filters car drives perfectly,but this is very annoying .The car as low milleage 63k miles,doesnt smoke and had 1 other carefull owner ,I mostly do short runs 7 miles to work and back ,But have done longer runs ,doesnt improve things much .Should I be getting much better MPG what are you guys getting .I posted in this section because its mostly 1.9tdi,s here .My hunch is the maf sensor or the thermostat but both were reading ok on VCDS ,thermostat was reading 1or 2 degs short of 90deg according to guy with VCDS,.
Thanks if you have managed to read this far ,and any thoughts ideas would be taken on board :)...

Short town runs are not mpg friendly.

Take the car on a longer (substantial) motorway run, keep the speed below 65 and see how your mpg fairs before forking out for new parts.

I'm amazed that people are so willing to spend money on apparently non existent faults. Derv lumps are only as economical as the drive they're taken on :-(



Sent from my Nexus 7 using Tapatalk 2

[ametlib]

ametlib: Overfuelling will make the car go faster, then you let off the throttle and hokus pokus, no overfuelling. What happens is, the ECU advances the timing ( due to the low temp reading) and actually improves the fuel economi !

So, if the CTS is under-reading you might expect for better fuel economy?
If the thermostat is not closing properly and the engine is actually colder than it should be, you would expect the fuel economy to be worse though?

Yes, if the CTS is slightly under-reading ( as in this case, 65 C instead of 9o C ) I would expect the fuel economi to actually improve. The reason is that the TDI engines ( from euro 2 and onwards) have a too retarded timing, seen from a MPG
point of wiew.This was done to reduce the NOX emissions. The remap guys knows this for a fact, and advances the timing a bit, and as they say it will improve the fuel economi.
However, if the CTS readings is too far out, the ECU will simply ignore the readings and calculate the timing advance based upon other sensors.
And yes, if the actual engine temp is too cold, as many have experienced, the fuel economi suffers.
BTW I woudn't expect too good MPG readings in the wintertime in cold wether. Here in Norway, with temperatures as low as -30 C , its easy to see the relation between temperatur/ fuel economi.Cold wether really isn't improving the MPG readings.

[adamss24]

I have a b6 audi a4 FWD with a freshly rebuilt engine and a few up rated bits thrown in the mix for good measure: bv43 turbo, EGR delete, lower CR- thicker head gasket, pd150 head bolts, valves lapped in and fresh timing belt job and i don't get better fuel economy than 44Mpg on motorway or 600 miles on a tank. I don't drive slowly either 90-110 Mph is normal as the car is very eager to pull since the new custom remap- so eager that i have already stripped the syncromesh on 3rd gear ! To say that i am disappointed with the fuel economy is an understatement, my 2 tonnes allroad with larger nozzles running on 20" wheels returns 32-35Mpg average and is 400-500 Kg heavier + permanent 4 wheel drive.
On a PD engine is important to set the syncro angle right, i found that setting it as close to 0 as possible will give up to 4Mpg increase in fuel economy and better/smoother power delivery overall !
Now that the box is goosed in my a4, i will do a quattro drivetrain swap- i have a b6 tdi quattro sport sitting on my drive with a broken timing belt- i wonder how the 1.9 Tdi will fare with 4 wheel drive and 6 speed gearbox with a longer final drive !

[Google44]

Update:

I've driven friends saloon audi A4 2001 and get 51 mpg with same driving style. I've had his MAF in my car - no difference. The car also had a bottle of Redex in tank with so far no difference at all.

The CTS is changed and now sits on 90 all time. The car pulls as it should but not done it lately as trying to improve economy.


Is there anything else to try?


As mentioned before I am dissapointed as B5 use to give me 50-60 easy.

If B6 is as good as this I will gladly go to BMW 525 diesel. However, if you think I could try anything else perhaps it deserves another chance :-)

[Eshrules]

Update:

I've driven friends saloon audi A4 2001 and get 51 mpg with same driving style. I've had his MAF in my car - no difference. The car also had a bottle of Redex in tank with so far no difference at all.

The CTS is changed and now sits on 90 all time. The car pulls as it should but not done it lately as trying to improve economy.


Is there anything else to try?


As mentioned before I am dissapointed as B5 use to give me 50-60 easy.

If B6 is as good as this I will gladly go to BMW 525 diesel. However, if you think I could try anything else perhaps it deserves another chance :-)

Over how many miles and at what speed was this test conducted?

Sent from my Nexus 7 using Tapatalk 2

[Google44]

It's a drip from Derby to London and back, totals to around 240 miles. Engine from cold with outside temp at around 4 C. Top miles 70 mph.

I've got VSDC and can record different blocks like MAF, timing etc. Not sure what to look for. The values seem to be OK.

According to one of the previous comments people get around 40+ anyway. To me that sound bad. VAG is known to deliver better then others. I use to get 45 mpg on TDCI 2.0 mondeo or BMW 525D. The quattro should be in this figures.

[Eshrules]

It's a drip from Derby to London and back, totals to around 240 miles. Engine from cold with outside temp at around 4 C. Top miles 70 mph.

I've got VSDC and can record different blocks like MAF, timing etc. Not sure what to look for. The values seem to be OK.

According to one of the previous comments people get around 40+ anyway. To me that sound bad. VAG is known to deliver better then others. I use to get 45 mpg on TDCI 2.0 mondeo or BMW 525D. The quattro should be in this figures.

What I would suggest is the same trip, same speed and see how your avant MPG compares to that - then you'll know for sure if there's a real MPG difference or if it's perceived.