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Mystery fuelling hiccup on 318iS?

Posted: Tue Jan 18, 2005 12:54 pm
by pogweasel
Time for a bit of head scratching....

Last night was driving down to London for work when my 318iS developed an odd fuel problem.

Firstly I noticed the economy gauge swing suddenly down to 15mpg for no apparent reason. Then the car spluttered momentarily, like a slight misfire or something. It felt like either too little or too much petrol. I'm inclined to think too little as there was no popping of unburned fuel elsewhere. At the time I was doing a steady 85 mph in 5th. This situation happened about another 5 times over the next couple of minutes. The ambient conditions were cold (+1 or +2 deg) with light rain.

As it happened the rain started to come down heavier so I natually backed off anyway. Don't know whether this helped or not as the problem then disappeared (and the needle stayed on the rigt side of 30mpg) and did not ocuur for the rest of the journey or on the homeward stretch....

So what do we reckon???
Bit of dirt in the system somewhere that has now righted itself, or a symptom of something more serious???

(It wasn't my night, all things considered: Not only do I suspect that at some point the exhast has dropped it's centre bracket and is now sounding a bit rattley, when I parked up at Earl's Court it was raining and I forgot to switch the wipers off when I switched the engine off....when I came to leave it was dry(ish) - the wipers got their knickers in a twist and collided with each other so now the left one struggles to complete a full sweep, and the right works but is bent to fcuk!! To add insult to injury I got "flashed" by an unmarked GATSO van on the A40 at 44ish in a 40 zone. ARSE!!!! :cry: )

Posted: Tue Jan 18, 2005 1:51 pm
by CaesarBob
I had something similar on my iS but that turned out to be the water pump which eventually seized solid. But it took about 3 months before it got to that.

Usually when driving along at steady speeds the car would feel like it was about to stall and then it would be happy as larry. The problem was intermittent but when it seized the car stalled with horrible squealing belt sound fx's.

hth

Posted: Tue Jan 18, 2005 2:25 pm
by Dom
water in a spark plug?

Posted: Tue Jan 18, 2005 2:27 pm
by Karan
cam/crank sensor also maybe

Posted: Tue Jan 18, 2005 4:10 pm
by Russ
I KNOW THE ANSWER!

A split in the pipe leading from the AFM into the inlet manifold!

With your foot down, the car sucks more air in, "sucking" on the pipe, opening up the hole.

When you backed off, the hole closed up a bit.

As the air leak is after the AFM, it wrecks the fuelling, causing a misfire and general loss of power.

Ԛ£12 for a new pipe.

Posted: Tue Jan 18, 2005 4:12 pm
by Russ
I KNOW THE ANSWER!

A split in the pipe leading from the AFM into the inlet manifold!

With your foot down, the car sucks more air in, "sucking" on the pipe, opening up the hole.

When you backed off, the hole closed up a bit.

As the air leak is after the AFM, it wrecks the fuelling, causing a misfire and general loss of power.

Ԛ£12 for a new pipe.

Posted: Tue Jan 18, 2005 4:19 pm
by Jhonno
we heard you 1st time :p

Posted: Tue Jan 18, 2005 4:28 pm
by johnono
:lol: :repost:

Posted: Tue Jan 18, 2005 6:29 pm
by mattjbatch
I had a similar problem on mine but it didn't matter how much throttle I had on. Turned out to be a dodgy fuel pump.

Posted: Tue Jan 18, 2005 7:57 pm
by Geeman
Russ got so excited that he might be able to help someone out at last, his fingers were trembling... :giggle:

:woohoo:

Posted: Tue Jan 18, 2005 9:44 pm
by Russ
Geeman wrote:Russ got so excited that he might be able to help someone out at last, his fingers were trembling... :giggle:

:woohoo:
:oops:

Posted: Tue Jan 18, 2005 10:39 pm
by Simon13
fuel pumps get nice an noisy for along time before they go. Listen to it on start up for a funny electronic noise from under the rear seats driver's side i think they are

Posted: Wed Jan 26, 2005 5:06 pm
by rare
Did you manage to sort this out?

I have just started having a similar problem, but only when I fill the car up. It carries on for about 15 minutes and then becomes normal again. The other night however, it idled at 3k revs after I fille dit up, making it bassicly undrivable, so I had to park up and come back to it half an hour later.

Its starting to get to the point where I cant drive it after filling it up. Becomes very unstable, just does not feel safe.

Posted: Thu Jan 27, 2005 8:13 pm
by E30Mark
Had similar probs with my iS couple of years ago, turned out to be the airflow meter. Always started and drove fine for 15mins or so, but would start to mis-fire the more i tried to drive it... a quick trip to the scrappie and Ԛ£50 lighter the car hasn't missed a beat since :D

Crankshaft sensor

Posted: Mon Jul 11, 2005 12:55 pm
by dinwoodie
Got exactly the same problem. BMW reckon it's the crankshaft sensor. I've ordered one (about Ԛ£40). I'll put it on myself as even a complete mechanical duffus like me can do so apparently. I'll let you know.

Posted: Mon Jul 11, 2005 2:45 pm
by rowemeister
Have you checked for killer rats living in your AFM. Very common apparently :D lol