Thirsty 318is

Wed Mar 02, 2005 3:36 pm

Every 318is owner i speak to 'claims' they regularly get 30-35 mpg. Mine however drinks the stuff like it's going out of fashion, and before you all start, no i don't hammer it around everywhere! Even when i'm trying my hardest to get a good return i'll average 19mpg over the week doing short trips to work and 28mpg on a decent run of about 100-150 miles on the motorway. Any ideas from the more technically knowledgeable out there?

Wed Mar 02, 2005 3:39 pm

Have you chipped it?
Leaky fuel tank?
Pinhole in a random hose?

Wed Mar 02, 2005 3:42 pm

is it heating up?

ie it should be at half on the dial.

Guest · Wed Mar 02, 2005 4:47 pm

as you know anyway short trips screw up your mpg but you should get at least 30 on a 100 mile jaunt...specially on a m-way, unless you're doing 90 for those 100 miles.

I once went from Dublin to Letterkenny, about 130 miles on normal Irish roads (read, crap ones) and took my time, overtook from way back without dropping into 3rd and caning it etc. and returned 47mpg !!!

Granted, the following week going to and from work across town that dropped to about 20-25.

Check your filters and the icv...maybe you're running rich ?

Wed Mar 02, 2005 5:47 pm

my old iS would return over 30mpg on the motorway 60-95 all day long, might be running cold so it just keeps pumping the juice in.
I used to get 25mpg around town too.
Has it got the proper plugs? old air filter?

Wed Mar 02, 2005 5:49 pm

Hmm i never got anything less than around 26mph around town, never got the miracle 45mpg tho!
Air filters always a good place to start like Simon said, most old cars ive bought have had black filters from years of not changing it!

Wed Mar 02, 2005 8:24 pm

When i used to use my iS everyday, i did a 65 mile trip, half on motorway, rest stuck in traffic, used to average 37mpg. The best i got on a run was 41mpg. With the viper2 chip the economy is worse, probably get on average 31 - 32 ish now. Putting the standard chip back in soon to see if the economy recovers.

ps318is have you checked the small rubber fuel hose that attaches to the metal fuel pipe coming up from the fuel filter? It's a bugger to see properly as it's nearly all hidden behind the inlet manifold, these are prone to splitting & leaking, but i'm sure you will have smelt the petrol by now.

Wed Mar 02, 2005 9:00 pm

I was running similar mpg. could also smell fuel in the cabin. Replaced the pipe mentioned above and can now get 30mpg around town if I girl it... changing gear at 2k rpm

Thu Mar 03, 2005 9:16 am

Thanks for all the replies to my problem guys. When i first bought it 8 months ago i could smell petrol which was leaking from the hose under the inlet manifold, which i replaced. The car is an absolute minter, FSH from BMW and a couple of Specialists, and looked after really well in general. Filters are fine, no other leaks but you may well be right about it running cold. My temp gauge normally sits just over a quarter, even when on a long run.

Thu Mar 03, 2005 10:48 am

thermostat stuck open? Also try running on small amounts of fuel, say 20 litres at a time to see if it is the fuel tank leaking. Mine leaks and by not filling it above half way none escapes!

Thu Mar 03, 2005 11:22 am

try adjusting the afm..

Thu Mar 03, 2005 8:46 pm

Not to hi-jack the thread but is the Viper chip any good? Can someone explain to me what they are like in real life and benefits.

Cheers,

Jim.

Fri Mar 04, 2005 1:48 pm

Jimbob wrote:try adjusting the afm..

Sat Mar 05, 2005 9:21 am

Interesting subject guys, and close to my heart!
My 318is after a Bosch tune when I got it, averaged 33.8mpg over about 6000 miles, driven fairly hard over mostly country lanes, A and B roads, not much motorway (albeit normal a-b road cruise speed about 80..).

Then quite suddenly this dropped to an average of 31mpg for no apparent reason. I had it tuned again but absolutely nothing wrong with it - the chap even commented on the evenness of the compression and fuelling across the 4 cylinders, being better than many new cars, apparently. (not bad for 155k miles I guess).

Anyway, I haven't resolved the problem, much to my frustration, but there is a clue, which is not helping me. The silly econometer vacuum gauge does indeed read about 3mpg lower on average then it used to, ie at a certain set speed, or on a very familiar and oft-repeated bit of driving. This to me just means that I am using more throttle, but physically I'm sure I'm not.
The performance and all engine characteristics are perfect and have not changed.
I changed the fuel filter yesterday, not that I'm expecting this to make a difference, but I also noticed a crankcase breather hose with a couple of small splits in it, which I've taped up in the short term.
There's no fuel leak, no dragging brakes, it has a free diff, tyre pressures are ok etc etc. Can't help thinking it's something to do with vacuum hoses. Anybody with any comments about this possibility?

I know this is a list of my problems, but hope that it may be useful to the author of the thread.
Someone mentioned the ICV. Why can this cause poor fuel consumption?
Cheers Jon

Sat Mar 05, 2005 1:28 pm

Jon your AFM could be worn.

Andrew

Sat Mar 05, 2005 1:58 pm

Demlotcrew wrote:
Jimbob wrote:try adjusting the afm..

Mine was adjusted by a matter of a few degrees and made a world of difference.

Sat Mar 05, 2005 4:08 pm

Worn AFM?
Would a very switched-on Bosch specialist not pick this up? And would it explain the relatively sudden worsening of the fuel economy?
If the answers are yes and yes, how is it adjusted? When I took one apart from a Bosch-injected VW boxer engine, it seemed a pretty delicate and non-adjustable piece of kit...

Sat May 06, 2006 11:12 am

Looks like I have the same problem with a fuel leak coming from the rubber pipe that connects the metal fuel pipe to the injection bar. For those of you that have replaced it - is it difficult to do? Do you have to take the mainfold off or do any other dismantling?

Cheers

Robin

Sat May 06, 2006 9:36 pm

I proabaly get around 30mpg (or just under sometimes) but then I drive like a cnut! Well actually not so much anymore, if I drove it like I used to drive my crx (keep it in the powerband ALL the time) then I'd prob be getting 10-15mpg! Yet I used to get the same 30mpg out of the 'rex

damn that car was good (apart from the front wheel drive

)

Sat May 06, 2006 11:26 pm

economy on these should be pretty good. Mine's spent a lot of this tank of fuel at full load (MAP) at WOT on the rollers as I've mapped the high load sites for my MegaSquirt. It did around 50 miles on the rollers iirc. I'll still get over 250 miles out of the tank - which will be better than 25mpg as i fill up normally with around 10 galls gone. around town i get a minimum of 30mpg without fail, motorway 35mpg+ depending on how quickly i'm going. I have a longer ratio diff that prob helps a tad, but not significantly. eleccy fan too. My car is fuelling properly (verfied by dyno session and its lambda readings etc), runs clean on a fault code diag and all the sensors are fine etc, and no vacuum leaks etc, putting out factory power. in short, i think its a fair indicator of what they should put out.

19mpg and you've got a fuelling problem. what do the plugs look like? have you had a diag done? have you tested the resistances of all sensors? there'd have to be something fairly bad wrong with it to be returning those sorts of figures imo.