1.8/2.0 TSI - tell me your idle fuel consumpotion.

[brad]

Can those of you with Mk2 Octavias with a 1.8 or 2.0tsi (or even the older 2.0 TSFI) have alook at your instantaneous fuel consupmtion read out at idle please?

I want to know with the engine at normal operating temp (say 15+minutes of use) and the gearbox in nuetral or park:
1) Consumption while idling with the econ light lit (ie: AC is off but blower is working).

2) Consumption while idling with the AC on Auto & econ light off and the temp set about 18/19 celcius. Ambient temp 25+celcius.

The reaon I ask is I think my AC compressor might be failing / dragging.

I get:

1) 0.8L/hour

2) 1.5 - 2.5L/hour (yes it varies that much).

When driving with AC on I use about 2L/100km more fuel with the AC on but i figure the idle reading removes all the variables such as road speed, hills, tyre pressures / type / width, driving style, etc.

thx

[OctaviaKid]

From memory I get between 1 and 1.7 with ac on in the 1.8, I will check after I go for a drive though

[woofy]

I'll check next time, but I remember coming home on some very hot days when it was new and letting it run for a bit to cool down with the A/C still on and it was around the 0.8-1.0 mark. That's the TFSI.

[harlie]

This test will give a wide range of variance.

You will need to set the temp to min to ensure the AC compressor is on full output (it’s a clutch-less variable output unit) or use VCDS to check for the HVAC ECU requesting full output (0.820amp). The compressor has 9 output stages between 2 and 100%.

Brad, it would be interesting to get a correlation between compressor output and instant fuel consumption.
In Auto HVAC you are wanting to check for;

005 Compressor current; actual value 0.??? A
006 Compressor current; specified value 0.??? A

006 is what the ECU is asking for, 005 is what signal the ECU has sent to the compressor. 0.820amp is 100%, anything less and I would expect fuel consumption to drop off.

Obviously as 005 counts up 078 Refrigerant pressure should be on the rise too. 116 Temperature after evaporator should be falling until very low single figures.

What’s 007 Compressor load ? Although I’m not sure where this comes from

Check the compressor is varying - Turn the temp back to 24. You should see both 005 and 006 drop off to something like 0.280 as the compressor goes into a low output mode. 078 should reduce, 116 will come up. The vent temp should rise to ~10.

The compressor has a sacrificial link behind the pulley, if it is dragging too much it should let go, however I’m pretty sure that in the event of internal failure it drags no matter what the switch position is.

2L/100 extra doesn’t seem right…

VCDS info is based on our MY10 facelift Octi (3T0 907 044 AL)

[Fourwinds]

Looks like harlie has given you more scope to work with ...........



2.0 TSi
0.8 (aircon off)
1.0 to 1.2 (aircon on)

[brad]

Thanks harlie. I'll reak out the VCDS cabe & have a play.

[harlie]

Fourwinds' numbers look more like what I would expect.

Brad, once you've confirmed that the AC is working as it should (have some faith). Next Question I would be looking at:
Is your fuel consumption actually rising by that much?

The car is reporting that it is close to doubling at idle but let’s face it, the car is only guessing based on some loose parameters - there is no meter in there actually measuring what's going through. The primary input is throttle position and if the engine is tuned there is a good chance that is now wildly inaccurate for the purpose of consumption calculation (tuning is not focused on the consumption readout). All going well, it's pretty close, but I wouldn't be surprised if the readout is crap. An increase of 2L/100 (what do you usually get???) is a good percentage increase, and I would expect it would also be feeling noticeably sluggish - that much drag on the engine is going to be noticeable through the seat as well. Are you pushing the throttle down 20% further?

Both our TDIs with this AC system don’t notice any difference in drivability with AC on or off. Fuel consumption is up slightly (about 0.2 – 0.5L/100 weather depentant)

The only way to confirm is a couple of tankful calculated the old fashion way (L pumped in / km travelled).

If the AC doesn’t look right with VCDS, and the car feels sluggish and really is using the fuel with the AC on then the compressor is looking pretty guilty - however, I'm sure we're not out of ideas yet - a compressor dragging that much just doesn't sound right.

[roshea]

Today's values for 1.8 TSI:
Idle without A/C normally 0.8 - 1.0 depending on electrics (heater / fan etc?). Most commonly at 0.8.
A/C 1.0 - 1.3 (possibly higher) depending on temperature difference between inside and outside.

[NOO63N]

Last I checked mine is
0.8-1 off
1.2-1.6 on

Will check again today brad, btw ended up keeping the car for now...

[NOO63N]

Just checked - 1.8tsi 6sp manual
0.8 idle no air con
1.4 idle with air con