What I discovered and did to overcome fuel consumption problem

[julianpang]

Just to share this with fellow brothers and sisters hereMy car is a E34 525i (M50B25) manufactured in 1994 with automatic 4 speed GM gearbox.I had the car since October 2011. Since day 1, I have been getting a range of 400~420km on a full tank ($130 RON95). Thats is pure PJ/KL city driving. I thought this was bad and I thought of improving it. I have seen friend's 525i getting about 450~480km per tank.So I narrowed down a few things to check on my car.1. O2 sensor possibly time to change.2. Possible stuck exhaust back box3. Might be gearbox since i noticed I have very mild slippage between 1st and 2nd. And also from 2nd to 3rd.What I discovered last week1. My car (local AB spec) doesnt not come with o2 sensor. There were no o2 sensor lubang at all on the whole exhaust system.2. I plugged in the OBD to get the o2 reading and I get constant 0.4v reading set by my car's ECU. If o2 sensor is there, the reading will flutuate. 3. My car does not come with a catalytic converter.4. I cut open my back box and discovered this. back box collapsed and condemned (refer to pic below)

What have I done after I discovered the above1. Bought and install new o2 sensor.

2. Bought a 2nd hand back box from chop shop. You got to shake it and make sure you dont hear loose bits in the box before you buy it.The end resultsAfter the above, I pump full tank to test the consumption. I have not finish my tank yet.Previously, when my car hit 50km mark, the fuel needle will move down slightly. So far with this tank, I have done 70km and the needle is still stuck at full mark.I will update once the fuel level go down or when I finish the tank. In terms of performance, low end torque feels about the same. However, I can feel improvement mid range to high range. Gearbox will be 6 months down the road since my mechanic told me to use until it condemn.

 

[Cressidom]

Julian..

..good info, please update when possible.

 

[haywire]

How do you install o2 sensor to a car that doesnt originally come with it? Need to cut the exhaust? Reprogram?

 

[julianpang]

How do you install o2 sensor to a car that doesnt originally come with it? Need to cut the exhaust? Reprogram?

The socket and wiring was already there. I jacked up a friend's Uk spec E34 and traced back where his o2 sensor wiring leads to. Then i went back to my car and did a "treasure hunt" and found the my o2 sensor socket at the exact spot as my friend's but mine had a dust cover cap on. Then i proceeded to ebay and ordered it with the correct part number.

On the exhaust part, i asked the exhaust shop to drill a hole at the same spot as my friend's car which right before the first box. Fyi, my car has front, mid and back box. None of them are catalytic converters which was confirmed by my mech and the exhaust guy.

If you have access to OBD, try to disconnect yoyr o2 sensor from the socket. I believe you will get the fixed 0.4v reading and your car will still idle and drives normal. If i am not wrong o2 sensor is only helping u on consumption for normal driving and also helps on emission.

 

[Eggie86]

Interesting. Thanks for sharing bro!

 

[docrayboy]

The socket and wiring was already there. I jacked up a friend's Uk spec E34 and traced back where his o2 sensor wiring leads to. Then i went back to my car and did a "treasure hunt" and found the my o2 sensor socket at the exact spot as my friend's but mine had a dust cover cap on. Then i proceeded to ebay and ordered it with the correct part number.

On the exhaust part, i asked the exhaust shop to drill a hole at the same spot as my friend's car which right before the first box. Fyi, my car has front, mid and back box. None of them are catalytic converters which was confirmed by my mech and the exhaust guy.

If you have access to OBD, try to disconnect yoyr o2 sensor from the socket. I believe you will get the fixed 0.4v reading and your car will still idle and drives normal. If i am not wrong o2 sensor is only helping u on consumption for normal driving and also helps on emission.

Well done, Julian! You are the Sherlock Holmes of BMWCM! Does the O2 sensor read differently now?

 

[julianpang]

Well done, Julian! You are the Sherlock Holmes of BMWCM! Does the O2 sensor read differently now?

I have not checked the reading yet but i will do it at my next visit to my mech.

If the o2 reading fluctuates, it means not only the wiring was pre-lay, the program is also pre-catered for o2 sensor. If it still stays at constant 0.4v, it means program is not catered and my RM384 investment on o2 from ebay gone down the drain. I strongly believe the program support since the socket was already there.

So far it seems like consumption improved slightly. But i am not sure if that was contributed from back box or o2 sensor.

 

[anakin]

Julian, I've had different case...my engine got 02 socket..my ekzos got 02 sensor's lobang (but covered with a srew)..when I first bought mine, she got very strong fuel smell whenever I start the engine..so after read here & there, without referring to my mech, bought a new 02 sensor..(pandai!)...bring it to mech, my mech say...my car don't need it!..I asked why? socket ada...lobang pun ada? He said the socket is there for newer version, whereas my car got older wiring which does not support the 02 sensor, in other word, newer engine but older wiring (89/90)...then the hole on the exhaust pipe? Well, the exhaust maybe had been replaced some time ago by the previous owner....about the fuel smell? He just tuned the AFM...... walla!!so there my RM500 02 sensor gone down the drain....

 

[julianpang]

Julian, I've had different case...my engine got 02 socket..my ekzos got 02 sensor's lobang (but covered with a srew)..when I first bought mine, she got very strong fuel smell whenever I start the engine..so after read here & there, without referring to my mech, bought a new 02 sensor..(pandai!)...bring it to mech, my mech say...my car don't need it!..I asked why? socket ada...lobang pun ada? He said the socket is there for newer version, whereas my car got older wiring which does not support the 02 sensor, in other word, newer engine but older wiring (89/90)...then the hole on the exhaust pipe? Well, the exhaust maybe had been replaced some time ago by the previous owner....about the fuel smell? He just tuned the AFM...... walla!!so there my RM500 02 sensor gone down the drain....

For 89/90 (M20 engines), the AFM can be adjusted. Refer to below for the adjustment screw.
http://www.bmwe34.net/E34main/Maintenance/Engine/AFM Adjustment.htm

Sadly, the AFM on my car (M50 engine) cannot be adjusted. M50's AFM is different from M20's. Before i did the o2, i could smell a bit petrol smell from the exhaust in the morning. I donno about now coz i have been having flu ever since i installed the o2.

 

[julianpang]

Anakin,

I just investigate further on your o2 sensor for your car (M20 engine). Actually, i believe your wiring supports o2 sensor. Maybe certain spec of E34 doesn't come with it for some reason. It would not hurt to try and poke it in and monitor since you already bought it right?

Why i believe your car or wiring supports o2?
That's because i can find o2 sensors made for M20 E34 year 89/90.
O2 and lubang already got. Just cucuk and try la.

http://www.ebay.com/itm/NEW-Bosch-O...ries&vxp=mtr&hash=item564110f3c6#ht_627wt_922

http://www.ebay.com/itm/BMW-E34-O2-...ries&vxp=mtr&hash=item413c53d279#ht_681wt_689

 

[smike]

Hi there guys. This info is the greatest i have read so far. I too sometime smell gasolne in the morning when i start.But only at times. Does this means my O2 sensor is having problem too. Pls advice. If it is how can i purchase one. Mine is a 525 5 speed with ZF gearbox. Pls advice. Cheers. S.Mike

 

[julianpang]

Not sure if my car still have petrol smell or not. But i can tell you.... My exhaust is very smelly especially in the morning. I think thats because my car doesn't come with a catalyst converter.

Just finished my tank today. I did 462km with $128.45 RON95 petrol. That's an improvement but I need to do a few more tanks to confirm coz this tank i was driving extra careful with the throttle. Next tank i will drive like normal people.

I have not get my o2 reading yet but i should get it done sometime this week to confirm if the ecu supports it.

 

[pussy]

why smelly in the morning is due the rich mixture of the cold start valve/sensor working.. once reach normal desired temp, then it will be normal....

 

[julianpang]

why smelly in the morning is due the rich mixture of the cold start valve/sensor working.. once reach normal desired temp, then it will be normal....

Normally I stand around the car in the morning while waiting for it to warm up. Thats why i noticed the smell in the morning.

I thought it smell like petrol earlier but my neighbour's opinion is not the petrol smell. HE said it smells very smelly but it isnt petrol smell. I believe that could be due to no catalytic converter.

Day time I dont notice it coz normally duting the day i just jump into my car, start then go. So I dont notice.

 

[julianpang]

UPDATE: I went over to my mech today. He plugged in the computer into my car. My car's ECU confirm can support O2 sensor. The reading was fluatuating according to my throttle. That's good news.

Will update again on fuel consumption at later stage.

 

[hkusj2]

HI Good evening guys! introduce my self my Henry very interesting infor on fuel com. since you guys own e34 i need check my e34 5201 m50 1996 model i have some problem on the car jerking if you stop at traffic lights the idling not that stable any one went thru this problem is it could be plugs or could ignition ?

 

[julianpang]

HI Good evening guys! introduce my self my Henry very interesting infor on fuel com. since you guys own e34 i need check my e34 5201 m50 1996 model i have some problem on the car jerking if you stop at traffic lights the idling not that stable any one went thru this problem is it could be plugs or could ignition ?

I had the same problem. Mine was caused by dirty throttle body. I am not sure about yours.

 

[julianpang]

I have done testing with my 2nd tank. This time, i drive a bit harder than the first tank which was my usual driving style.

This time i get 435km with $132 of ron95.

Conclusion is not much of a difference with the o2 sensor.

So.... My next project will be rebuilding my old and worn out auto gearbox. It's has got some slippage since a long time ago.

With the new gearbox, i hope to get better fuel consumption. I will get it done after CNY holiday and i will update the results here.

 

[pussy]

Julian, i have been following your thread and what you are doing is good to increase your milage and fuel comsumption, but you are not doing enough...
My V8 3 liter gives me 530km to a RM138.00 full tank.

To get there, you will need to do this:

1. Tyres, must be good condition, correct tyre pressure and use Michellin tyres with 'X' marking, gives you 6% in fuel savings.
2. aligment of tyres better have less tow in, use zero toe, better rolling resistance.
3. Engine, make sure proper oil is used,
4. All hoses and make sure no air leak, intake hose, breather hose good.
5. Throttle body clean and crankcase return hose free from sludge.
6. Valve cover and dip stick no oil leak.
7. Service your MAF or AFM with the cleaner form CRC. adds better hp and nice idle.
8. Service your injectors, balance it and do a test leak.
9. make sure your fuel regulater is working plus the vacum hose is good.
10. TPS at the throttle body working.
11. Fuel vapor purge valve is working, if not, can cause rough idle and loss of power.
12. All rib/v-belts working and alternator giving good output charge.
13. battery is good condition and reads 14.2volts when engine on.
14. O2 sensors must be good too and proper readinga achieved.
15. Running gearbox and rear diff with good oil, new at 40k kms is good.
16. Your spark plug gap is good and even burn.
17. check your plug coils also is good ohm rating. check also the rubber boot.weak boot, can cause arching, misfiring.

hopefully this will make your FC better.

 

[julianpang]

Thanks a lot. Based on your check list, i will pay special attention to 4, 5, 7, 8, 9, 11, 16 & 17. The rest are all ok.

My injectors has leak. I could see wet spot around some of the injectors. I will get that replaced