terrible mpg

[pjw]

ok, im sort of getting towards the end of my tether with this a4. its a 1.6 8v, and i would have expected at least mpg above 30.

i put £50 in and got just over 200 miles, which in anyones book, is terrible. works out just about 25mpg, if not less.

so, ive looked on vagcom and theres no engine fault codes. the temp is reading 90 on the dash, and the temp is reading 87.5 on vagcom. i cant access the fuel trims on block 032 for some reason, but i can browse other blocks, but i dont know what im looking for (ie a number, a percentage etc)

ive replaced the ignition system and had no change.

i dont even boot it either - since putting this 50 quid in ive been doing a few 70mph runs, and usually i drive it to work and back which is a 9 mile trip at about 40 mph with no overtaking or overrevving.

the tyres are all pumped up.

the only thing i was thinking about is that due to the 19"s the speedo is misreporting, but it wouldnt be by 50 miles!

can anyone please point me in the right direction please, im on the verge of getting rid of it. i could run a v6 for this money.

 

[ScottD3]

There seems to be alot of people moaning about poor MPG at the moment and i'm about to be one of them.
I've lost over 10mpg on my display. I use to get about 46mpg, now i'm lucky to get 36. I got a couple of things I need to check/replace. thermostate, temp sender and a complete VCDS scan. May be a serivce.

When was your last service?
Fuel filter, spark plugs and so on?
Does your car sit at 90 or does it move around?
Have you thought about putting a standard air filter on and see if that makes a difference?

 

[aragorn]

Its really hard to give a specific figure and it really depends on your driving.

the old 1.8T FWD would do 32-33mpg if the ENTIRE TANK was used up on the motorway, This would drop off sharply if driven around town, to more like 27mpg. Quattro uses more because its heavier, more like 30 and 24 respectively

Your first problem is this "i put 50quid in and it did n miles", its completely useless as a guide, as you dont have a solid reference point. Fill the tank to the top, and reset the trip. Drive for a bit, then brim the tank again, and compare the fuel you've put in, with the miles on the trip counter.

If the cars actually burning that amount of fuel, it must be mega rich, which points to either the MAF or Lambda sensor. It'd also struggle to get thru an MOT like that imo.

 

[Road Razor]

Possible fuel leaks or the fuel filter isn't properly secured(?), or leaks on the fuel lines/breather valve in the engine.

My 2.4 V6 would normally do 25-26mpg in town and 32-34mpg on motorways. My dad used to own a '96 1.6, I can't give you accurate figures but its fuel economy is way higher than what I achieve on the 2.4. I think the 1.6 should be capable of at least 40mpg on motorway.

 

[MrJoshua]

My 2.4 V6 (AGA) gets a displayed 18-22MPG around town and only just 30MPG on a long run down the motorway I must boot it too hard from the lights or something!

To the OP - If your journey is just 9 miles each way, I expect that for a lot of that journey, the engine oil temperature is fairly low. Is there much stop-start on the run to work and back?

 

[pjw]

There is a fair amount yes but nothing to justify 25mpg from an 8v 1.6. Ive had other cars with the similar engine size and beyond, and never known it to be that bad. Im running out of things to look for to be honest.

I really need to try and find the fuel trims on vagcom and see if thats ok. Fingers crossed its out and its something i can fix.

 

[pjw]

As an additional, i have put the original airbox back on too.

MAF is reading the correct g/s inputted into the engine for the revs. (82gs for 110bhp @ redline).

Its going if this is the standard MPG for this engine, i can faster cars for this price.

 

[aragorn]

Fuel consumption in general has little bearing on engine size (unless you use ALL the extra power thats available from the larger engine, all the time), and infact can go the completely opposite way to what you'd expect.

Accellerating 1300kgs of car up to 30mph requires a certain amount of energy. Similarly crusing at 70mph requires a more or less constant amount of energy. Given the energy comes from petrol, then for the most part, it will be the same irrespective of the powerplant.

A Big v6 will tend to use a bit more, but this is mainly due to the frictional losses of the extra two pistons and the car being slightly heavier etc. You'll notice above that the figures quoted by the V6 chaps arent all that different to those from the 1.8T however.

Similarly an old 8v motor will be less efficient at converting petrol to motion than a newer 20v turbocharged engine, so you'd expect the older design to do a little worse. Further to that, if the engines underpowered, you spend longer periods at large throttle openings trying to get the car to accellerate, which in turn uses more petrol.

I remember a few years ago me and my brother drove from scotland to a car show down south. We were both driving Vauxhall Nova's his being a pretty standard 1.2i and mine have been fitted with a 1.6 16v motor. We drove down probably a little faster than the speed limit most of the way, but i remember being surprised at the first petrol station he managed to fit quite a bit more petrol in the tank than i did. You'd have expected the little 1.2 to use less, but because he was effectively thrashing the guts out of it for 4 hours whereas the 1.6 was crusing along happily, the 1.6 had used less fuel.

Having said all of that, i'd still have expected more than 25mpg from your car. Its lighter than a 1.8T model and so should be returning better or at least equivalent economy. I'd be tempted to stick a new lambda sensor in it, as its about the only thing that could cause it to go rich without also developing a fault code.

 

[sk8xtrm]

Im driving a 96 1.8t and ive had appauling mpg recently and been chasing this for ages and i didnt get a fault code either. I found few things that affected my mpg badly. 1) my lamba needed replacing as one of the wires had frayed not giving correct signal (still no fault code) 2) Cold weather, i live near brecon beacons and we had ridiculous lows of -18 at one point but averaging - 5 most days. Once it warmed up my mpg went up a fair wack to. 3) 18" wheels, try smaller wheels if you dont find a fault with the engine. they do affect mpg a little. Hope this helps alittle