very very poor mpg....why??:(

[doughboy]

tech 2 sport. only mods are bbtb & wild chip.

stick 20 quid of unleaded in and the light comes back on after about 60 miles.

I don't drive hard, only put my foot down now & again for short bursts.

It's used for a few miles each day to & from work.

Anything I should look into?? Cos surely something aint right??

[Brianmoooore]

Leaking it or burning it? What colour the spark plugs? Any smell of petrol? Any puddles under the car?

[doughboy]

No puddles and no smell..

Booting it gives a dark cloud out the back so I'm told.

Will check the plugs tomorrow.

Cheers

[Brianmoooore]

Sounds like the plugs may be black then, indicating it's running rich. Standard answer, assuming it reaches normal temperature on the temp gauge, is to check/replace the blue Ecu temperature sensor.
Top front of the engine on the water outlet elbow with a blue connector.

[Jon_Bmw]

I make that to be 13 Mpg! roughly anyway. Surely not just the blue temp sensor can be causing that. I agree its definatly the best starting place anyway. Is it a very short distance you drive, is the engine always cold, also when you say you boot it a bit, thats a bit hard to interpret. People that have claimed to drive economically when i have been a passenger in their car, clearly don't

[SPADGE]

I make that to be 13 Mpg! roughly anyway. Surely not just the blue temp sensor can be causing that. I agree its definatly the best starting place anyway. Is it a very short distance you drive, is the engine always cold, also when you say you boot it a bit, thats a bit hard to interpret. People that have claimed to drive economically when i have been a passenger in their car, clearly don't

If the blue ecu temp sensor is telling the ecu the car is cold all the time then it most certainly could be the cause!

[Jon_Bmw]

I would have thought perhaps about 20mpg instead of 30, but 13 seems proper low. Driving type and style will definatly play a bit part too i think. Still in agreement that a dogey blue temp sensor is most likely cause of "poorer" fuel consumption.

[SPADGE]

I would have thought perhaps about 20mpg instead of 30, but 13 seems proper low. Driving type and style will definatly play a bit part too i think. Still in agreement that a dogey blue temp sensor is most likely cause of "poorer" fuel consumption.

The guy says he doesn't drive it hard though
I once had a 320 that was worse of fule than my 535i and this turned out to be the temp sensor! If it were my car i would run it down to a garage/mot station and get it hooked up to a co meter to see how the fueling is and maybe get it adjusted assuming it isn't the afm thats at fault.

[Jon_Bmw]

I would have thought perhaps about 20mpg instead of 30, but 13 seems proper low. Driving type and style will definatly play a bit part too i think. Still in agreement that a dogey blue temp sensor is most likely cause of "poorer" fuel consumption.

The guy says he doesn't drive it hard though

Arg, if you read my first post, i get at the fact peoples opinions of driving a car hard differ.

Also as far as i know, you can only adjust the CO at idle, not under any load situations, so whilst that might be helpful slightly i can't see that benefiting it to the stage where it is back to normal(30mpg) conditions. 3rd time, i agree blue temp first port of call.

[alan325i]

MY 325I is not reaching normal temp, stays just over the blue hardly ever goes to the quarter mark when heaters are on and im recieving 18.8mpg according to the OBC

So to get only 13mpg i'd check the fuel lines for cracks, (you wont get a puddle of fuel under car if slightly cracked) check fuel mixture and make sure ur tyres are at right pressure as well

So Blue temp, thermostat, fuel lines, tyres pressure, fuel mixture and air filter need to be checked. Oh and take out the lead in ur right shoe

[mikey-t]

take the handbrake off before driving

[timmyboy]

is there an easy way to test that sensor thingy???

[Nelly]

^^There's not - there cheap enough to replace though.

I'd be tempted to check all around the breather pipes, given the fact that most of our cars are now going on 17 years old, all the rubber will start Pershing - causing air leaks.

Neil.

[doughboy]

Looked at plugs today, they're brown not black.

The coolant sensor gave just over 2k ohms when cold and about a quarter or so of that after 5 mins idle.

What I did notice however was the vac pipe form inlet manifold to the fuel pressure regulator was blowing, so I fitted a new one.

The temp gauge works fine and comes to rest at about half way.

When I say booting it, I mean flooring it in usually 1st or 2nd all the way to the redline.

My daily journey is only a few miles. I don't have time to warm it properly in the morning, but give it 10 mins idling at night before driving.

[DRIFTBOY]

Short journeys are a killer for miles per gallon!

So is leaving the car idling - then it's doing zero miles per gallon!

[daimlerman]

When er indoors uses the 316i just for her trip to work(1.5 miles each way)the thing will only return 17mpg.When I use it for my trip to work(21 miles each way)I can get upto 38mpg.Constant running when cold eats fuel.

[del_320ise]

I just thought that was the norm, i only get about 14.5 mpg out of my 320i and sometimes i can smell petrol and the car is a little smokey but not excessive smoke. What can this be ?

[Jon_Bmw]

14.5 you thought was normal, some "supercars" will return more than that...until thrashed.

Good ol 320.

[Dr Firefly]

But the 320i is a supercar......... isn't it?

[Jon_Bmw]

So it is, that must make 1.6 corsas uber supercars

[doughboy]

I knew short journeys were bad, but I thought that was mainly due to the oil not being at a decent temp.(Hence 10 minutes warmup before leaving work). I didn't realise they'd affect mileage so adversely.

I'll stick another 20 quid in tomorrow and see what happens now that the new vacuum hose in on. The old one had almost split the whole way through.

[DRIFTBOY]

When I had my old job 7 miles from home through the town centre my old Mazda RX7 used to average a tank of fuel at just under 10 miles per gallon!

[pnd]

BMW dont recommend idling the car before driving unless its very cold and then only for a few seconds (see manual) also it uses a lot of fuel and is very bad for the enviroment three good reasons why its a dumb thing to do.

[doughboy]

BMW dont recommend idling the car before starting
its a dumb thing to do.

Thanks I'll make sure to start it before letting it idle.

So basically I may as well ride my bike to work and use the BM at the weekends.

Does make sense though, a full tank(50 ish quid) town driving I'm lucky to get 200 miles... But on a long motorway stretch I can get 330 maybe.

E30s make crap(ie overly expensive) town cars then

[Globulator]

What I did notice however was the vac pipe form inlet manifold to the fuel pressure regulator was blowing, so I fitted a new one.

Fuel is injected from the fuel rail into the manifold. A low manfold pressures therefore will tend to 'suck' the fuel out of the injector faster.

The vacuum pipe allows the fuel regulator to track the manifold pressure, to always present a fixed pressure between the rail and the manifold, which in absolute terms may mean it varies a whole lot! This means that for any manifold pressure, the injectors inject the same amount of fuel for the same opening timing - i.e. the ECU does not have to worry about manifold pressure.

If that pipe leaks, the regulator increases the pressure of the fuel rail to combat the atmospheric pressure it now reads from the pipe. The manifold pressure then sucks a whole lot of extra fuel in each time.... overfueling your engine.

So I think you may have just solved it: assuming your blue sensor is working fine (brown is gauge only).

[Globulator]

BTW:

If you want good cold-weather starting and economy, stick some decent 0w40 synthetic in (from Opie perhaps), it has miles better anti-wear properties, less friction, and flows properly when cold therefore reaching all the right places quickly and needing much less energy to pump around.

Also don't use/ration the heater inside until the engine is warm. Make sure your thermostat is a good'un. Check obvious things (blue sensor/vacuum pipe as above)

Not sure is there are tips for the gearbox/diff oil for winter - any takers?

[dobbie82]

is there an easy way to test that sensor thingy???

as nelly said, cheap enough to replace about £16 for a genuine bmw one

my 320i got really pi**ed at me doing four 4-mile journes a day! it never got warmed up and drank patrol. Yet on long runs it was as economical as my 318i.

[doughboy]

Cheers all, I think I may as well change it since it's cheap anyway. Will check the thermostat too. I assume the opening temp will be stamped on it somewhere. I guess the test is have it cold then chuck it into a cup of hot water and see if it opens.

I'll give 0W40 a go at the next oil change too.

[del_320ise]

What I did notice however was the vac pipe form inlet manifold to the fuel pressure regulator was blowing, so I fitted a new one.

Fuel is injected from the fuel rail into the manifold. A low manfold pressures therefore will tend to 'suck' the fuel out of the injector faster.

The vacuum pipe allows the fuel regulator to track the manifold pressure, to always present a fixed pressure between the rail and the manifold, which in absolute terms may mean it varies a whole lot! This means that for any manifold pressure, the injectors inject the same amount of fuel for the same opening timing - i.e. the ECU does not have to worry about manifold pressure.

If that pipe leaks, the regulator increases the pressure of the fuel rail to combat the atmospheric pressure it now reads from the pipe. The manifold pressure then sucks a whole lot of extra fuel in each time.... overfueling your engine.

So I think you may have just solved it: assuming your blue sensor is working fine (brown is gauge only).

Can somebody explain that to me a little easier pweez !!!

[DRIFTBOY]

I think he means the split vacuum hose wasn't helping matters!

[del_320ise]

I think he means the split vacuum hose wasn't helping matters!

Thanx Driftboy

[Globulator]

Sorry guys, the summary:

A split vacuum tube to the regulator = high fuel pressure = too much fuel squirted in