From digest.v7.n426 Mon Oct 13 01:41:17 1997
From: Brian Brown <bpbrown_at_execpc.com>
Date: Sun, 12 Oct 1997 23:54:24 -0500
Subject: Re: Gas - Guzzling 318

> From: "Kameron A. Cole" <riviera_at_mwci.net>
> Date: Sun, 12 Oct 1997 12:05:21 -0500
> Subject: gas-guzzling 318
>
> Bimmer Boys:
>
> My 84 318i is getting progressively sicker. I wrote a few days ago
> that
> it wouldn't return to idle when the clutch was depressed, and I'd like
>
> to thank those who sent me some good advice. But the big problem is
> that the engine is being overfed fuel, which just gets wasted, stinks,
>
> and blows smoke out the exhaust. Especially in 3rd, the mpg guage
> shoe
> 12 mpg! It takes a quarter tank to get to the grocery store! Now, it
>
> doesn't happen all the time (just most) - sone days, the sun is
> shining,
> and the Great Spirit grants me a few moments of the old pleasure of
> not
> stopping at stops signs, gliding past miles of seemingly stopped
> vehicles - you know. But then,back to the gas station. When I get to
>
> 4th, the mpg's improve to 15; then, in 5th, I make it to 20. But, I
> used to get 30-40 mpg intown. I really need your help.
>
> - -k
>

Most likely it's the air flow sensor.

To check the air flow sensor, remove it from the car by loosening the hose clamp on the bellows, and by loosening the three nuts that hold it to the air cleaner housing. It should then just slip out of the housing.

Check to see if its flap is sticking or binding. It should have smooth movement and it should spring back fully shut when you release it. If it sticks, it's bad.

If the flap wasn't sticky, carefully peel back the rubber boot of the connector that plugs into the air flow sensor so that you can measure voltages while the connector is plugged in. Remove the fuel pump relay (on the driver's side inner fender under a plastic cover with two other relays, it's the one towards the front of the car). Make up a jumper wire that you can put in place of the relay's pins 30 and 87 ( look at the relay to figure out the pin numbers). With the ignition on and the relay jumper wire in place, make the following voltage measurements at the air flow sensor:

Pin 9 (red-white wire) to pin 5 (brown wire): approx. 12 Volts Pin 7 (grey-yellow wire) to pin 5 (brown wire): approx. 1 to 6 Volts, varying smoothly up and down when the flap is moved.

If the signal is erratic, or doesn't change, the sensor is bad.

If the air flow sensor passes these two tests (I don't think it will), then the problem could be a leaky fuel injector or a bad L-Jetronic control unit.

There could be a secondary problem with your car. All that extra unburned fuel could be clogging up your catalytic convertor. If you're lucky (and haven't been driving the car too long with this problem), then the convertor won't be plugged, or it may burn itself clean after the root problem has been fixed. If you're not lucky, then you also may need a new catalytic convertor.

My '84 318i had this problem this summer. I was traveling across the country and I was in the desert near Death Valley when the problem occurred. Let me tell you that it's not very pleasant to do troubleshooting when it's over 100 degrees and there's sand blowing in your face. I limped the car into the nearest city (about 70 miles, it took almost the full tank of gas). I rented a car for a couple of days (this took place on a Saturday) while I waited to get a new air flow sensor (Rodd Sidney was able to get one shipped out to me faster than anyplace else I tried). When I put the new sensor in, the car was still running rough and blowing a bunch of smoke (from the cat). It took almost an hour and 60 miles of driving before the car gradually started running good. I was lucky.

Good Luck,
Brian Brown.
BMWCCA #130878
'84 318i (still running good w/over 200,000mi) '84 528e
'96 318tiS (picked up after returning from the above trip)