High Fuel Consupmtion After Service?

[kev_ 0]

Hi Guys,

I have a Japanese 1996 E36 328i Auto, and I have noticed that my fuel consumption has risen drastically after giving it a service.

Basically:

1. BEFORE SERVICE: fuel consumption is normal, performance is a bit sluggish.

2. AFTER SERVICE: fuel consumption is terrible, performance is fantastic.

The service took me a few weeks to perform, as I'm pretty busy, and I was waiting on some parts to arrive; the car was off the road for the entire time (4-6 weeks) it took me perform the service.

Here is what I did in the service:

1. Oil change (BMW/Castrol oil from dealer)

2. New oil filter (OEM brand)

3. New spark plugs (OEM/Bosch)

4. New air filter (OEM)

5. New valve cover gasket (replaced all rubber washers while I was at it)

6. Replaced the center driveshaft bearing & assembly with new units

7. Cleaned the cat temp sensors with isopropyl alcohol while the exhaust system was removed from the car

8. Attempted to reset the ECU and transmission adpations by: A] disconnecting battery for a few hours B] turning the key in the ignition until the dash comes on, and then pressing the gas pedal to the floor for 30 secs

I also installed a front lip, which required me to remove the font bumper and disconnect/reconnect the temp sensors in the brake ducts.

After having performed all that, the car drives amazing! The idle rpm is perfect, and the car is back to its smooth, responsive, grunty self - it drives like new! Also, the jerk from 1st to 2nd has completely disappeared!

...but now the fuel consumption has gone through the roof!

I'm just about to replace the fuel filter and clean the MAF sensor, but apart from that, does anybody have any ideas on where I can start looking?

Could this be a result of attempting to reset the ECU and transmission adaptions?

Edited March 11, 2012 by kev_

[kev_ 0]

...oh and just to add, I've done about 50 kms since the service (car has done 105,000 kms in total).

[BM WORLD 1260]

you are flooring it more , also let it sit around and idling while increase the fuel usage,

better to test it over a week or 2 of driving normally

also double check all your plugs and hoses are conected back in place etc

[Allanw 1051]

Did you clean the cat temp sensors, or the oxygen sensors? I don't know if the o2 sensors would like Isopropyl???

[M5V8 337]

Is the gearbox holding gears longer and not changing up when it should?

[jom 96]

you are flooring it more , also let it sit around and idling while increase the fuel usage,

better to test it over a week or 2 of driving normally

also double check all your plugs and hoses are conected back in place etc

Fuel consumption on an auto 328 can vary a lot depending on how you drive it.

For example a day at Manfield for the sprints uses a tankful, more or less.

It's 150km to Manfield for me, it uses about 1/4 tank. That's 10l/100km for 100kph road driving.

1/4 tank on the way back as well (tank is 65l) means it's using 30l to do 20 laps - at 2.5km/lap that's 50km... consumption is up to 60l/100km or so. Now that is foot either on the throttle, hard down, or on the brake, but you can see the difference.

Even I didn't believe this while I was typing it. Man that's a lot of fuel....

...but it equates to 4.71 mpg, which is better than I remember a G1 Camaro doing.

Jo

Edited March 12, 2012 by Jo M

[hybrid 1039]

Get the car scanned to see if the O2 sensors are now out of range and throwing up an error. Cleaning may have well damaged them. Thus putting the DME into default safe fuel trim program which will run the car more rich. (uses more fuel)

Sometimes an easy way to tell is if your getting black soot build up on rear bumper / tail light area more than usual.

[kev_ 0]

Thanks very much for the replies guys

you are flooring it more

Hmm, that's what I thought at first, so I made sure to drive 'sensibly', and it's still guzzling gas.

Did you clean the cat temp sensors, or the oxygen sensors?

I cleaned just the temp sensors (the long, needle-type probes).

Is the gearbox holding gears longer and not changing up when it should?

The gears are changing at exactly the same points as they were before the service for both sports and economy mode. If anything, the shifting has become drastically smoother now.

Fuel consumption on an auto 328 can vary a lot depending on how you drive it.

For example a day at Manfield for the sprints uses a tankful, more or less.

It's 150km to Manfield for me, it uses about 1/4 tank. That's 10l/100km for 100kph road driving.

1/4 tank on the way back as well (tank is 65l) means it's using 30l to do 20 laps - at 2.5km/lap that's 50km... consumption is up to 60l/100km or so. Now that is foot either on the throttle, hard down, or on the brake, but you can see the difference.

I know exactly what you mean; I can get about 6.6l/100km for 100kph road driving, and about 1/2 that for city driving, but 60l/100km around Manfield - damn, that's nuts!

Get the car scanned to see if the O2 sensors are now out of range and throwing up an error. Cleaning may have well damaged them

I didn't touch the O2 sensors at all, but could something else put them out of range? E.g., installing a new air filter?

I've read that it can take a couple hundred kms for things to return to normal after disconnecting a battery, so I'm not too worried at this point; as Brent suggested, I might give it a couple of weeks and see what happens - maybe it'll come 'round by itself.

[KwS 2377]

i would expect the car to run rich after having the adaptions on the ECU reset, as to my understanding it takes time for the ECU to lean the mixture out depending on factors whilst driving.