30MPG at 60-80mph - 325i. Problems? Advice please!

[Adil786]

I just did a 100 mile trip after restoring my cabbie back into shape. I know e30s can be thirsty, but I am worried that there may be a minor sensor problem or something.

On the flats in cruise, the car was getting about the 30mpg mark on the "fun meter". This was for speeds of between 60 and up to 80mph. The owners' manual claims about 40-44mpg.

It's a 325i cab, 1990 manual with a genuine 80k on the clock. The car has been serviced, valves are adjusted, and she pulls well.

Anyone else had/has the same problem? What could I check? Lambda sensor, MAF etc?

[Cloggy Saint]

You call 30 mpg a problem?? Most people wouold rip your arm off for that!

[StuBeeDoo]

As Datourer said, 30mpg is fair. The econometer doesn't really tell you anything about real-world fuel consumption, and neither does the figure you've quoted from the handbook.

[DaveD]

The MPG meter is just a guide....take it as just an indication of how light footed you are. I get 25-27 overall in my 325 cab but did 450 miles this weekend ..mostly motorway but including a trip in heavy traffic round London and it returned about 34/g on the trip

[raj1980]

i get 20mpg, you should be happy.

[e30newbie]

Ok, I have just done the maths, you would have to drive like a real grannie downhill with a strong tailwind to get anywhere near 40-44mpg at 60-80mph. The best I ever got out of my 325 cab cruising (driving like a human for a change!!) at around 100kmh (62mph) over about 300kms (190 miles) was 7.7litres/100km (36.7mpg), no traffic involved.

Be happy with what you have methinks.....

hi willnz,

how many kms do you normally get out of a full tank ?

I have a 88 325i cab auto and the best I can get is about 11.5 litres/100km

[ivqii]

My long term average is 23

[kura2]

my 320, city driving 20 litres/100 km

[Adil786]

Hmm, interesting figures. I did more digging around....

The 30mpg figure is AT cruise, not an average. The average is less, and much much less with city driving!

[quote="willnz"]If you are concerned, check that the blue temp sensor is reading correctly at operating temp, it will affect the mixture if it is out. Should read 300-360 ohms at normal temp.

Thanks willnz, I'll take a look at that.

I also found a link about AFM adjustment of someone hooking up a live logger to their lambda sensor and making some tweaks while driving to get the right oxygen reading to check the fuel-air ratio. I guess this is the rolling road alternative! I'll find that link and post it up.

Another link of fuel to air ration is: http://www.dtmpower.net/forum/e30-3-ser ... -rich.html

I know this only affects idle, but car showing symtoms of rich "blip test". Carbon deposits on the plugs too - grrr, new plugs too

Will let you know how this progresses....

[mrLEE30]

if i get 400km out of a tank then its very good, i fill at 350km(220miles) but i live on a small island so almost exclusivly city driving. this is a 325 manual, but running A/C all the time, but the Mtech 2 kit helps by a few hundred metres per tank .

I almost made 440km before the light went on a few weeks ago but that was in saudi on a highway doing 120-130km/h (70-80mph) but the tank was not 100% full when i started so not sure of the real range, i also dont like the light coming on.

for comparison my wives Dodge Durango AVERAGES 24 litres/100km!! that translates to 360km from a 80-90 litre fill up!!!

mlree

[mrLEE30]

what are you on about?? fuel in Bahrain is expensive we pay the equivilent of 40 NZ cents per litre, this is twice the price of Saudi Arabia where fuel is really cheap at 25NZ cents per litre..... so really we have it quite bad!!!

It always brings it home to me when i visit UK, i hired a Deisel V70 volvo and almost passed out when filling it up, both due to the price of a full tank and the effort of standing up as here in bahrain we arrive at a station, crack the window half an inch (too hot to open fully!!) pass out the required amount of cash and someone comes and fills it for you!!

And you'll love this, despite the cheap fuel prices in Saudi, and the fact that they fill it for you, they still give you a free gift when you manage to spend more than 25 riyals (10 NZ bucks) - they give you a box of tissues!! See what i mean the Saudis have it good while we suffer in Bahrain!!

[jon552]

and we currently pay NZ$ 1.72 per litre, that is why I am insanely jealous of your 40c/litre

nope sorry mate not expencive, in the uk we dream of 72p/l try paying £1.04/L (NZ$2.50/L) for a while

mrLEE30 could you send me a dozen drums of unleaded please you can keep the free tissues. At that price i would just let the rangy idle all day as back ground music

jon

[Brianmoooore]

in the uk we dream of 72p/l

You can have your fuel for considerably less than that if you invest a bit of time and a few hundred quid in a LPG conversion!

[mrLEE30]

welcome back mr moooore!

[Morat]

\o/

[Adil786]

OK, update time! Car oil seviced last week now, plugs etc still in good nick, tappets done recently, 82k miles. Temp sensor working spot on. Some AFM/MAF allen key adjustment done - idles well

£40 fuel lasted me 200 miles = 23MPG average

This was 120 miles motorway (cruising at 70) and 80 miles city driving, VERY conservative <insert boring driver smiley!!>

I thought I'd get more from a - what I think - is a healthy engine

My goal is to make my 325i cab my daily driver, so from all these threads I think the only way is economically feasible is, like BrianMoore has said, LPG conversion - or ask my boss for a big payrise

I think I know how this is gonna end - watch out for my LPG threads

[N00b]

Depending what type of driving the OP typically does, it's maybe worth mentioning diff ratios and their effect on economy.
If you tend to do the lions share of your driving on the motorway it might be worth your while fitting a higher final drive.

[minicooper172]

I could scrape 440 miles out of a tank every weekend on an M20B25. I can't remember if it was a standard tank or not. However, this was on pretty much 100% motorway driving, and driving like someone much older than I am, but at the speed limit. Which is quite contradictory.

[Adil786]

I think it's the 4.10 final drive - she's about/under 3000 rpm at 70mph.

Minicooper172 - 440 miles? HOW THE F***!!!! JEALOUS!!!

So what's up with my engine, why so thirsty? Is it even worth considering the LPG investment if she's a bit of a dog to start with?

I know how to drive 'economically' - it was a pain for me to even achieve the numbers above. I can get 48mpg on the motorways with my N42 engine at 70mph with cruise control on...

[N00b]

I think it's the 4.10 final drive - she's about/under 3000 rpm at 70mph.

Minicooper172 - 440 miles? HOW THE F***!!!! JEALOUS!!!

So what's up with my engine, why so thirsty? Is it even worth considering the LPG investment if she's a bit of a dog to start with?

I know how to drive 'economically' - it was a pain for me to even achieve the numbers above. I can get 48mpg on the motorways with my N42 engine at 70mph with cruise control on...

First decision is "can I fit the LPG conversion myself?". If yes, then in my opinion it's a no brainer and you should go for it.
If you can't fit it yourself then bear in mind that as long as you buy decent LPG kit, it will roughly halve your fuel bills for the duration of your ownership AND you'll be able to either sell the car for more than the going rate or sell the kit on in here.....recouping some of your money.

[Adil786]

Additional info:

I've got original 16" alpinas with good tyres on here (goodyear eagle f1) - fronts @ 33psi, rears @ 35 psi.

Tech2 kit, with tech2 spoiler.

Car is lowered on springs by about 30mm.

Has a Sebring back-box, on standard 2-piece exhaust.

"885" head.

No aircon

PAS

No other features/mods.

I'm only going down the LPG route if I have the confidence she'll last me 2 years at least (mechanically).

Maybe I need a real e30 expert to give the car a diagnosis. Are there any dyno days at a e30 expert garage coming up that I can get the car dynod and checked over? I did something like this with e46fanatics dot com for about £35 per car. Really useful and built up good links with the garage. Maybe i need to put a post on the group buy area or something.

[stonesie]

I think it's the 4.10 final drive - she's about/under 3000 rpm at 70mph.

Well mine dose 3K rpm at bang on 70 with it's 3.73 diff, with its origional 4.27 it was about 3.5/3.6K


Without going to a M3/Z3 diff you wont get the revs much lower for motorway cruising.


The only thing i can think of that might improve your economy aside from LPG is to get the injectors cleaned properly (redex wont replace the little filters and all that)

[minicooper172]

Minicooper172 - 440 miles? HOW THE F***!!!! JEALOUS!!!

That's what I get out of my E36 328i, too!

I just drive at the speed limit, I guess. I keep the revs down, never above 2k unless the gear forces me to (for instance, 5th gear at 70MPH).

[Adil786]

Yep stonesie you're right, it's the other way around with the diff ratio (d'oh), it's 2000rpm @ 50mph = 2800 rpm @ 70mph, so about 3.64 give or take.

[e301988325i]

I think it's the 4.10 final drive - she's about/under 3000 rpm at 70mph.

My 3.64 does a satnav speed of 75mph 3000rpm, I'm running 205/55 r15s. Wider tyres add more drag. . .

Poor economy could also be thermostat related, does it warm up quickly and stay there?

[Adil786]

I think it's the 4.10 final drive - she's about/under 3000 rpm at 70mph.

My 3.64 does a satnav speed of 75mph 3000rpm, I'm running 205/55 r15s. Wider tyres add more drag. . .

Poor economy could also be thermostat related, does it warm up quickly and stay there?

Yep gets to temp fine and stays there. Sometimes a bit cool, sometimes a bit warmer (depending on interior heater setting) - but always in the right area. Should I change the stat?

[hezicar]

I've managed over 400 miles a couple of times in my 325i cabriolet.

Once cruising all day to the south of France on super unleaded at circa 80-90 mph.

The other time in the uk on 95ron cruising on the motorway at 80 mph (very little town driving).

Best MPG I've ever recorded was 34mpg when a mate of mine was driving when we were sharing the driving and I'd fallen asleep, I think he was a little nervous driving on the wrong side of the road in France!!

[Low_E30]

Some AFM/MAF allen key adjustment done - idles well

What has this been adjusted too?

Any figures? (CO%)... You would need a gas analyser to do this by the way....

What was the CO level before you started adjusting?

Going to get my one done soon at a friendly MOT station, as Im suspicious that its been messed with previously.... Would like to know what is the benchmark/optimum CO% figure for a stock factory healthy M20 2.5?

[Bob_S]

think you need to buy a diesel 106 matey

[bobbin1982]

If you want a cheaper drive... i suggest a 1.6 lol