MPG problem

[Husbandofstinky]

The best i have had was last weekend with some motorway driving averaging 54MPG over a 65 mile run at ( 70 to 75MPH) on the way there and 47MPG ( 75 - 80 MPH) on the way back.
Most of the time over 40 mile round trip to work and back ( town and country driving) I generally get mid 40's, high 40's if stuck behind tractors etc.

That sounds pretty bang on to what I'm getting. So I'm

 

[Djag]

Am I missing something here. I drive a 1.9 TDI FR with a 45L tank. Most of my driving is around town with the odd country run or motorway trip. Only once have I got 400 miles from a full tank and even then it clicked over to 400 miles as I rolled into the petrol station. I then brimmed the tank with 41L of diesel. I therefore only got 43.9mpg.(400 miles divided by 9.11 gallons) For this 400 miles I also did more coasting that i thought was possible. Is my engine faulty or is this forum full of bullsheeters.

 

[the_fbi]

Am I missing something here. I drive a 1.9 TDI FR with a 45L tank. Most of my driving is around town with the odd country run or motorway trip. Only once have I got 400 miles from a full tank and even then it clicked over to 400 miles as I rolled into the petrol station. I then brimmed the tank with 41L of diesel. I therefore only got 43.9mpg.(400 miles divided by 9.11 gallons) For this 400 miles I also did more coasting that i thought was possible. Is my engine faulty or is this forum full of bullsheeters.

I think its more a question of the type of driving you're doing.

My first ~4.5 miles every morning is 30-50mph with a number of roundabouts, short country lane section, 2 mile uphill section, few more roundabouts (with traffic lights) then 9 miles of dual carriageway (very slightly uphill).

I won't get my trip average above 44mpg till I'm around 8 miles into the journey. By the end of the trip to work, which is 52 miles, of which ~23 is motorway ~18 is dual carriageway, I used to be averaging 62+.

If I go from my house around town, I'm lucky to get 40mpg for the trip (~5 miles) as its all stop/start.

Ibiza FR is the same as mine, apart from mine has slightly better (less rpm) gear ratio in 6th, no idea about a Leon FR though, it may be similar.

That said, somehow I've lost 8-10 mpg which I really am feeling in my wallet. So its possible whatever is now wrong with mine is also wrong with yours.

Seeing as a new MAF didn't fix it, and consumption appears to be OK at cruise (constant load/speed) my next investigation will be the vnt mechanism as clearly thats affected by load. Although I don't know if the MAF actual being way above the MAF specified when under load is pointing this way too.

Below shows a short section of rpm against MAF specified and MAF actual.

RPM Spec Actual
1680 735 617.4
1785 850 994.7
1911 850 1234.8
2079 850 1249.5
2205 850 1249.5
2310 850 1244.6
2436 850 1249.5
2541 850 1200.5
2625 850 1180.9
2142 365 328.3
2079 845 1029
2121 830 1058.4
2142 790 984.9
2142 555 725.2

I'm guessing as way too much air is coming in, the ECU is putting in more fuel to compensate? No idea though really.

To answer your question though, stick her in cruise at 70mph on a motorway for 10 minutes and you should see a nice increase in your average. Instant MPG should show around 63mpg depending on hills etc.

 

[ChrisGTL]

Am I missing something here. I drive a 1.9 TDI FR with a 45L tank. Most of my driving is around town with the odd country run or motorway trip. Only once have I got 400 miles from a full tank and even then it clicked over to 400 miles as I rolled into the petrol station. I then brimmed the tank with 41L of diesel. I therefore only got 43.9mpg.(400 miles divided by 9.11 gallons) For this 400 miles I also did more coasting that i thought was possible. Is my engine faulty or is this forum full of bullsheeters.

I just got 420miles from my last full tank, my low fuel light had been on a good 10 miles too.

That said, somehow I've lost 8-10 mpg which I really am feeling in my wallet. So its possible whatever is now wrong with mine is also wrong with yours.

Seeing as a new MAF didn't fix it, and consumption appears to be OK at cruise (constant load/speed) my next investigation will be the vnt mechanism as clearly thats affected by load. Although I don't know if the MAF actual being way above the MAF specified when under load is pointing this way too.

Below shows a short section of rpm against MAF specified and MAF actual.

Same as me. I've lost about 8MPG. Wasn't sure if it was down to me not doing any really long constant speed journeys, so took the car on the motorway @ 70mph (36 Mile roundtrip) - The only way I can get my MPG above 44 is by coasting....then I can see 48-52MPG but as soon as I need light throttle again it drops to 44MPG.

VAG-COM shows my coolant is 90.1C so I don't think my thermo sender is fubar. But mine is the old black sender so might replace with the revised green one.

MAF (mg/R)

RPM Spec Actual
903 335 279.3
1617 570 671.3
1659 600 592.9
1743 560 588
1827 550 534.1
2058 850 1127
2667 850 1249.5
3255 420 720.3
2121 680 1205.4
2037 315 519.4
1953 315 509.6
1848 315 504.7
1680 320 480.2
1596 475 431.2
1617 530 455.7
1659 625 553.7
1785 850 901.6
1911 435 646.8
1470 450 475.3
1407 465 666.4
1428 335 494.9
1365 335 509.6
1344 335 509.6
1302 335 514.5
1281 335 504.7
1239 335 470.4

Pressure

RPM Spec Actual
987 1020 1152
1176 1176 1080
1638 1524 1344
1701 1476 1536
1806 1500 1560
1890 1668 1596
2331 2676 2592
3108 2436 2988
2058 2604 2040
2079 996 1812
1995 996 1344
1911 996 1236
1806 996 1200
1596 996 1176
1596 1416 1224
1638 1488 1368
1722 1788 1572
1869 2220 2100
1764 996 1608
1449 1668 1392
1407 996 1368
1407 996 1212
1365 996 1164
1323 996 1152
1302 996 1128
1260 996 1116

Car still has no VAG-COM errors, just don't understand where my MPG has gone on long motorway trips....I even checked my tyres to make sure they were on 33PSI.

 

[MOZ_LC_TDI]

I'm pretty sure my tank on the Cupra TDi takes 55 L not 45, hence the extra 100 miles.

i have just been to Milton Keynes and back ( round trip of 360 miles) computer MPG showed an average of 51MPG and most of that was 80MPH, the fuel Guage is only just below the 1/2 mark and the computer is estimating another 240 miles left in the tank . From experience mine isn't linear and drops off rapidly as the guage falls below a 1/4 ( hence i don't believe the estimation) but I am expecting to get 570 miles out of this latest tank full.

i haven't had less than 490 miles in 10 fills mostly around the 500. honestly no Bull

Regards.


Moz

 

[ChrisGTL]

I'm pretty sure my tank on the Cupra TDi takes 55 L not 45, hence the extra 100 miles.

i have just been to Milton Keynes and back ( round trip of 360 miles) computer MPG showed an average of 51MPG and most of that was 80MPH, the fuel Guage is only just below the 1/2 mark and the computer is estimating another 240 miles left in the tank . From experience mine isn't linear and drops off rapidly as the guage falls below a 1/4 ( hence i don't believe the estimation) but I am expecting to get 570 miles out of this latest tank full.

i haven't had less than 490 miles in 10 fills mostly around the 500. honestly no Bull

Regards.


Moz

How many miles do you do per trip?

 

[MOZ_LC_TDI]

Hi ChrisGTL,
Sorry I have been away.

i usually travel about 22 miles to work in a morning and back again at night. so approx 45miles ish per day, plus a few here and there in an evening. Then depends on senior managements plans for the weekend as to what trips we have then.

Regards.

MOZ.

 

[Dave H]

coolant temperature sensor replacement. My old faulty one was reading -34*C, therefore more fuel was being used. A sign would be that the revs on start up are higher than normal. I was experiencing about 1100 rpm on idle at traffic lights, after 5 minutes of driving. Situation now resolved with new coolant temperature sensor.

 

[twig]

I've got similar problems on my mk2 tdi. Used to get high 50s, sometimes 60mpg with plenty of motorway miles but it's recently dropped to 53 and 44 on the last 2 tanks, still majority of motorway miles. the only I can think might have changed is when it had its MOT, they adjusted the brakes so I'm wondering if they're binding slightly. I've never looked at the brakes so has anyone got any tips for what I'm looking for when I get the wheels off? I'll probably try to run VAG-COM tonight too, see if any errors come up.

any help's much appreciated cos it's really doing my head in!

 

[Dave H]

winter, colder damper days influence the mpg, it is normal to get a drop with diesels during the colder months (well I do anyway, about a 5-8mpg variation from summer to winter). there are a few external environmental factors that effect the car. although first thing to check, and check regular is the tyre pressure.
in twigs case i would say the high 50s = summer; low 50s = winter; mid 40s = tyre pressure to low (increased load?)

 

[Jonboy582]

I too had a drop of between 7 - 15mpg completely unexpectedly. I took it to the garage and they ran a diagnostic and said they could not see anything wrong. But they re flashed the bios to make sure.

I am starting to think maybe the fuel we are using is not as high quality maybe as it was a few months ago?

 

[alex88]

Iv got a ibiza cupra tdi with 10,000 miles and im getting around 40mpg with around half of my driving on motorway or a roads. does this seem a little low? I know diesel engines free up as they do more miles but i was hoping for better mpg when i bought it. I get around 41-44mpg doint between 70 and 80, is this normal?

 

[Jonboy582]

Depends how fast you get to your speed and how break/accelorater happy you are.

 

[twig]

Checked the tyres & re-set the ECU but didn't notice much difference. But, I checked my brakes and it turned out that the handbrake wasn't releasing properly. Took the rear drums apart and cleaned / re-greased the mechanism and now I'm back to seeing high 50s/possibly 60ish on a motorway drive It's well worth checking - just jack the wheel up and try to spin it. Should spin easily and continue for a few seconds after you let go.

 

[alex88]

Depends how fast you get to your speed and how break/accelorater happy you are.

Just normal most of the time and putting the foot down on the odd occasion

 

[twig]

Sounds low to me. Would have thought you'd get 50 on the motorway.

 

[Jonboy582]

I would expect it to be a bit higher but the winter might play some affect. Mine has dropped loads aswell too.

 

[dribbler]

Hi, My MPG has also dropped 5-7MPG in the past 6 weeks,this on 450 miles a week ,60% motorway rest local. Used to average 55MPG but now down to 49MPG Must be the cold!!!!

Dribbler
Toledo 110 Tdi

 

[RobTheHood]

Winter tends to kill my MPG by the amounts given (5-7) I reckon it could be normal and not the time of year to test it out. After all with lights on more and more demand for cabin heating that can't help matters.

 

[loadswine]

I think you guys are doing pretty well. My Altea 2.0 TDI DSG has just recorded its all time low of 25mpg on the last tankfull. Air filter has been cleaned a couple of weeks ago, it has a new fuel filter and doesn't seem to run that badly. I'll clean the MAF tomorrow and may even spring for a new one , but its only done 46k!
Something is wrong somewhere, for sure, its never done much more than 30 round town before , but 25 is just crazy for a diesel.