PD130 TDi - Very low MPG!

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
My MPG is atrocious, mainly been used on short journeys (5-10miles), however, my fuel light came on at 200 miles after a full tank. Trip computer says im getting 40-60mpg on most journeys however.

Any ideas? Car cuts out at the top of 4th gear and goes into limp mode aswell, could be connected, has been remapped and isnt grannied.

MAF sensor? Coilpacks?
 

muddyboots

Still hanging around
Oct 16, 2002
5,739
1
Doubt it'll be your coilpacks, given that TDIs don't have them ;)

But yes if it's going into limp mode then there's something obviously wrong - you could do with scanning for fault codes with vag-com.
 

timbotdi

Active Member
Oct 18, 2006
213
0
Tis most likely the MAF, but could also be sticky turbo vanes, thick oil, etc...

A diagnostics test is the best way forward really...

Let us know how you get on.

T
 

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
Will get VAG COM on it. However, if the trip computer is reading a fairly positive outlook of 40-60mpg and im actually getting 20-30mpg- would it be the MAF?
 

daveyonthemove

Smile if you like SEAT's
May 14, 2006
1,519
0
Wrexham
There isnt a puddle under the car - ive checked that.

The fuel leak is more likely to happen when it's being driven as the fuel pump would put pressure through the fuel lines.
Maybe get someone to follow you up the road as it's being driven and look for any misting or drips of fuel.
Out of interest, what brand of fuel do you put in it?
 

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
Will get someone to look. What do you mean by misting? from the engine bay?
thanks for the help aswell - much appreciated.

I put in texaco fuel usually. thats where i filled the tank. I had some redex in at the same time. Hope its not bust something :(

It sounds expensive though if there is a leak.
 

mrcoyote

See no evil...
Jul 26, 2004
2,624
0
Do you always fill the tank up to the brim or just until the pump stops? Also have you tried venting?
 

daveyonthemove

Smile if you like SEAT's
May 14, 2006
1,519
0
Wrexham
By misting, i mean if the fuel hose is split or punctured the fuel might be coming out at such a high pressure it could Mist rather than drip.
Might be from the engine bay, but also could be under the car. I would expect there to be a strong smell of fuel though if your losing 25ltrs of fuel.
I'd definatly try VAGcom if you can just incase a sensor is faulty (you are sure the fuel gauge isn't faulty?).
I sometimes find an ECU reset helps bring things back to how they should be, so maybe worth a go.
 

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
If i reset the ECU will i need the radio code. That could be a problem.

I cant smell diesel usually unless ive just filled up :) Sometimes at night there is a mist coming from under the bonnet, a very fine one usually when its cold. I put that down to condensation, havent seen it for a good while.

I usually fill it uptil it clicks off as ive heard its bad to do more - however, i usually only put in £10 in a time as im a student and there is a petrol station just down the road. Whats venting (excuse my ignorance again :) )

thanks for your help so far. Much appreciated!
 
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daveyonthemove

Smile if you like SEAT's
May 14, 2006
1,519
0
Wrexham
I'd be concerned at mist coming from under the bonnet as all hoses/pipes/connections should be air tight.
If it was fuel misting you would smell it, so i think you can rule that out.
Venting: In the filler neck there is a small "button" usually on the left side. this can be moved forward when filling up and allows the air to Vent off faster so the fuel goes down the neck to the tank with less chance of splash back.
Reseting the ECU will require a radio code.
 

muddyboots

Still hanging around
Oct 16, 2002
5,739
1
By misting, i mean if the fuel hose is split or punctured the fuel might be coming out at such a high pressure it could Mist rather than drip.
I think all the high-pressure lines on a PD are internal to the cylinder head so you shouldn't be able to get very high pressure leaks.
You just have a lift pump in the tank (pretty low pressure) and then the tandem pump on the end of the cylinder head which supplies fuel to the injectors (and on the PD engines, it's the injectors themselves that generate the stupidly high injection pressure). I don't thing the pressure generated by the tandem pump is mega high.

And anyway, as has been said, if the mist were diesel it would stink.

The mist is a bit weird though, unless it's just the engine or exhaust drying off after a damp night. Either that or oil vapour leaking from the crankcase ventilation somewhere...
 

Lippo

YNWA
May 8, 2006
395
0
Formby
If you're doing 200 miles on a £10 of fuel that's pretty good... Have you accurately measured how much you are putting in your tank when you fill up?

Fill your tank to the first click on the diesel fuel pump (like you do normally), note the mileage, then when the fuel light comes on, fill the tank to the first click again and you can then work out what your mpg is by dividing the miles driven by the gallons you have just put in your tank.

My Ibiza is remapped etc, and I can do 635 miles to a tank, doing over 53mpg. It's not driven lightly all the time either. I use Millers Power Sport Diesel 4.
 

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
I did that if you read the first post :) I got 200 miles from a full tank (albiet fuel light to fuel light) its not driven slowly most of the time and at this time was used mainly for short journeys. so it worked out at about 25mpg. I was at the time using Redex - and now im using Millers 4 instead
 

Lippo

YNWA
May 8, 2006
395
0
Formby
You mentioned the distance travelled, but not the amount of diesel put in, so it's impossible to work out ith any degree of accuracy what your mpg is. You mention in a later post that you put a tenner in - that's 2.3 gallons which would equate to 85mpg!

200 miles is a rubbish range for your car, although fuel light to fuel light is very vague.

As for your car cutting out, there's something wrong there - but there's not enough info to diagnose what it may be, although you do mention a remap. Who did it?

I use Redex occasionally, and it's made no difference to my mpg. My route to work is 21 miles, a mixture of fast A roads, country lanes and motorways, so my car gets warm etc, whereas if you're only doing 5-10 mile trips, the car never gets warm enough to become economical, particularly if you doing city driving.
 

Mattyh87

Sideways as always!
May 7, 2006
220
0
Manchester
my fuel light came on at 200 miles after a full tank.

That would equate to approximately 25mpg (2 gallon reserve tank, 10 gallons in total)

I know the fuel light can come on earlier depending on how the car is driven. But it seems its drunk quite a bit to get through that amount of diesel. Usually, the journey is onto a motorway immediately so 80+ cruising for upto 7 miles so it warms up fairly quickly.

I think the cutting out is due to the engine being overfuelled - so it cuts out to preserve itself (think it was superchips who did the map).

Im going to drive my car like an angel for a full tank and see how it goes on, no matter how difficult it will be :)
 

craig-pd130

Full Member
May 7, 2003
353
0
Manchester
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Even with the journey you describe you should be getting into the 40s.

I've tried with my Passat to kill the MPG and (if the journey is more than 10 miles or so) I'll still get mid to late 40s. On a longer motorway journey I'll still get 50+ even cruising at over 90
 
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