Volkswagen Mark IV Forum banner

Status
Not open for further replies.
1 - 20 of 43 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Hi,

Can anyone shed any light my Fuel Economy Problem?

Over the last 4 months or so I've been experiencing much lower (~45MPG) fuel economy than I used to get (~53MPG) on my 104K mile 2001 VW Golf 1.9 GT TDI 130. To me this drop is a bit more than I'd expect with winter diesel (mostly Shell).

I don't drive like a loony nor do I drive like my Grandad but I do try to stay within the speed limit. I don't drive during the week and the car sits in the garage but on Friday night and Monday morning I drive 70miles each way to my girlfriends on the motorway (75-80mph) with town driving on Sat & Sun.

I've noticed that on a busy motorway run where I stay below 2000 RPM I get the economy (53-55MPG) I'm used to but if I drive at my normal 75-77MPH speed (~2200) RPM I get 45-47MPG (Note: this is average over the 70 mile journey).

I've had a service at Awsome GTI last week and asked them to check out the common things - MAF & Temp Sensor but both check out fine. It seemed odd that the economy is poor only when the turbo kicks in (2000+ RPM) so I asked Awesome if the Turbo Inlet could be cracked (another common cause apparently) but they said that would show up on the MAF readings (or as part of the MAF tests).

To complicate things about 5 months ago I installed a mini PC in the car (www.mp3car.com) but I can't see how a basic 90W 12v DC/DC power supply would cause enough of an increased load on the alternator to cause the MPG figures to drop by nearly 10. I've tried running without the PC connected but it creates a v boring journey (all my music is MP3 on the PC) and when I have done the traffic was poor so I was below 2000RPM so did not expect to see the poor figures.

I am now completely stumped - any clues on what else to check would be v much appreciated.

Cheers

Simon.
 

·
Registered
Joined
·
2,090 Posts
Mine did this last weekend on the trip down to cornwall from london, came back up on friday and the economy was back up to +/- 55mpg. The only thing i've changed was the tyre pressure at the rear which I had found to have dropped. *tut tut to me for not checking them!!* Especially dropped on the rear left, but then i've found the rear left to loose pressure the most of time, can't think why though to be honest!! Hope it's someting as simple for you!!
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #4 ·
Thanks for the suggestions - I am prety sure that it is not the first two

Tire Pressure - I don't check as regularly as I should do but when I do they are either at the recommended pressures or not significantly above or below.

Brakes - I had replacement disks and pads all round in January and this didn't fix the problem so I don't think this is the case

Also on both of these I can't see how they will produce the effect of good economy upto 2000RPM but poor economny above 2100RPM.

Outside Temp - How big a difference would this make really make. I suppose Winter Diesel, Lights, Wipers, PC, Stereo, Climate Control on Auto and Outside Temp could all add up to a noticable drop in the MPG figures but I am still struggling to see why it is much worse above 2100RPM.

I could be adding 2+2 =5 but could the Turbo activating (@2000-2100RPM) be linked somehow? However, there doesn't seem to be anything "wrong" with the Turbo - the car pulls strongly, there is no nasty noises - the only effect appears to be the poor fuel economy. Could the activation of the Turbo cause the car to "overfuel" hence increased consumption? If yes, what is the reason for this and how can I confirm or eliminate it?

Cheers

Simon
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #8 ·
Mike - I have seen other posts indicating that 45MPG is not uncomon in PD130s but this is counter to my experience. Since buying my Golf 2 years ago I was regularly getting 49-52MPG average over long runs at 75-80MPH but it only started to drop recently, hence my concerns.

Trying to find similarities or differences to explain the similar MPG figures - do you have an uprated ICE system or do you drive "enjoying the torque" [;)]
 

·
Registered
Joined
·
459 Posts
Ermm sorry for stating the obvious but the more your engine revs for more fuel your using, hence lower mpg over 2100rpm
 

·
Registered
Joined
·
372 Posts
My average so far is 45mpg but thats mainly local running and some hilly routes. It does seem odd though that your fuel consumption has dropped what you usually get - I don't think your PC would have a noticable effect on the consumption. Now that the weather is getting warmer, (hopefully) it will be interesting to see if your consumption improves again.
 

·
Registered
Joined
·
990 Posts
erm, am I the only thinking that your MPG seems about bang on the money. I get 45mpg in my PD130.
That's because you have those mega wide rear wheels[:p]

I manage about 42mpg in mine.
 

·
Registered
Joined
·
2,313 Posts
erm, am I the only thinking that your MPG seems about bang on the money. I get 45mpg in my PD130.
That's because you have those mega wide rear wheels[:p]

I manage about 42mpg in mine.
My "mega wide rears" are my show wheels only though! I run on 17" Audi S3's most of the time.
 

·
Registered
Joined
·
1,228 Posts
During the last 4 months I averaged 42-45, now over the last couple of weeks with the milder (but not hot) & longer daylight, I'm edging up to 50 mpg again, expect 50 + in the warm (but not hot) weather...
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #18 ·
Interesting - I hadn't considered the clutch being a possible cause - it doesn't seem to be slipping as I don't detect any rises in the revs without an increase in speed. Any one any good ways to check the cluch without taking the car apart?

There appears to be a pattern with those who are reporting 45MPG as not unusual most appear to have 17" wheels. I have the bog standard 14" wheels with standard tyres (same now for over 12 months so were giving the 50+ MPG). There is nothing uprated in the car other than the PC.
 

·
Mk4 for 13 years
Joined
·
993 Posts
Mine has 15" avus 2's and the figure of 45mpg sounds fine to me - its about what I get too.  Are you going off the figure on the dash?  What sort of miles do you get to a full tank of diesel?  Mine is around 470miles.  Climate always on AUTO, mostly town driving with the occasional outing.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #20 ·
Diesel, thanks for that - I always calculate the "exact" MPG figures based on miles and fuel used from fill to fill as I've found that the in dash figure tends to read higher than real life. I get about 470 - 490 Miles per tank 47 litres however these are mostly motorway miles so I would expect higher figures.
 
1 - 20 of 43 Posts
Status
Not open for further replies.
Top