Lower MPGs?

Ok, 2003 TDI Beetle. 170k, all original that I know of. TB done around 100k.

So normally I average 52-48 MPG and last tank I got 42 and this tank is shaping up to be as bad or worse.

No smoke, boost seem to be normal. All temps normal. Runs smooth. Power seems a tad low when cruising (go pedal seem to need to be pressed a bit more) but when WOT good power. Evry mod works as it has (on a toggle switch, not used often). So I am at a loss as to where all the extra fuel is going. I don't smell a leak or see fuel on the ground so I don't think its that.

I read around the forums and found some common information in this issue and checked a few things. MAF reading changes with RPM. Checked timing and injection quanity at idle.

23:00:15 Group 013: I.Q. Idle Stabilization (Injection Quantity Deviation)
0.19 mg/str IQ Cylinder 1
0.33 mg/str IQ Cylinder 2
-0.61 mg/str IQ Cylinder 3
0.05 mg/str IQ Cylinder 4

23:00:15 Group 002: Idle speed
903 /min Engine Speed (G28)
0.0 % Accel. Pedal Pos. Sensor 1 (G79)
0 1 0 Operating condition
75.6°C Coolant Temperature (G62)



Timing was done and according to other sources the engine was over 80C according to VCDS outside of the timing graph.

So does anybody have a clue where I should look to repair this? Thanks.

Forgot to add that I have had an engine light for a year but its for glow plugs.

17056 - Cylinder 2 Glow Plug Circuit (Q11)
P0672 - 35-10 - Electrical Fault - Intermittent

I checked it a year ago with a meter and all the GPs read the same resistance within .2 ohms. I tried to clean the harness thinking it was that but no go. I figure I just need to replace the whole harness. I don't think that that has anything to do with my crappy mileage because my car was averaging 48-52 with the GP issue.

Thanks.

It has been cold in Indiana. You get lower mileage when it is cold.

That CEL could be for more than one DTC. I would rescan the ECU.

I hope it just the cold weather. I have had this car for years and don't recall it ever getting this low MPG. I will continue to drive it and see if it makes any changes in MPG over the next month. If it is still low, could it possibly be the timing or injectors? I hope it just the cold weather.

Turns out it must have been a combo of cold and huge headwinds that caused 2 tanks in a row to be 42. Its back up to 52 now that its a bit warmer and no winds.

I have driven in similar conditions before but never got that low. Oh well glad it was nothing.

Your engine temp is a bit on the cold side- you want to be running around 90C or higher- diesels are happiest when hotter.
Also, tire pressure is critical- higher tire pressure = lower rolling resistance which means better MPG. Cold weather drops your tire pressure.

Pugsley said:

Turns out it must have been a combo of cold and huge headwinds that caused 2 tanks in a row to be 42. Its back up to 52 now that its a bit warmer and no winds.

I have driven in similar conditions before but never got that low. Oh well glad it was nothing.

Click to expand...

Unless you do/did a lot of short trips (and given your 'before' mileage numbets' I suspect not) it was mostly the headwind (although a couple of tanks of steady headwind would be unusual) causing your mileage drop. I live where its cold, a lot, and still keep my average over 50 thru most of it. The last two tanks have been 52 mpg and all of that was sub-freezing, and a fair amout of sub-zero F.
Wind is a very big factor. Mileage with a 20 mph headwind/tailwind will vary 10 mpg given the same speed over the same route.
Most of the time it avaerages out over the course of a tank, but not always, I guess.