High fuel consumption - 520iA

[arnoldmatusz]

Hello out there

I'm writing in to ask any opinions about why I have such a big fuel consumption on my E34 520i.
I'll some preeliminary things so we avoid unneeded posts!

1. I have a normal driving style - not rushing it
2. I've been to a diagnosis with it where I had an O2 sensor fault (which I've replace with a new one (Hella) - there have been no other faults (MAF ok, Injectors ok, Flywheel sensor, Camshaft sensor).
3. I've have no leaks at any (vacuum) hoses.
4. Service with new airfilter, NGK spark plugs, (oil of course)

No for what I consider is a high fuel consumption: it does around 21l/100km (which is somewhere equivalent to 11.2 mpg) urban and around 12l/100km extraurban (approx 19mpg). Other 520i owners tell me they are getting 12-14l urban and 8-10l extraurban?

Is this consumption normal and are other users ashamed to tell me their real values? Or is my bimmer dying shortly ?.

[ArnZ]

how many kms or miles has the engine done? if too many or engine hasnt been looked after then it might just be a worn engine.

just for reference my e34 535i gets 14L/100km in the city.

[arnoldmatusz]

Hello

Thanks for the speedy reply!
My bimmer has 200000km's on the clock. That shouldn't be an extreme number. I know many other BMW owners with much more km's and allot less mpg.

The engine looks like it's been well looked after. (the headgasket has been changed lately, this means I had the occasion to look inside the top of the engine, where it does not show any unusual wear/tear. The mechanic even said it was well preserved.

What I can also report about the symptoms is that it doesn't have much power low down and it begins to pull well somewhere above 3500 rpms.

[ArnZ]

in my honest opinion not even my 535i has a whole lot of power down low in the revs. let alone a 520i would have much either.

200,000kms is nothing for that engine so im not sure why the bad fuel consumption. maybe someelse in this forums (that has more knowledge) can be more of help

[DIL]

You have the M20, right?

[arnoldmatusz]

Nope it's the M50. (no VANOS).
Thanks for the reply.
Hopy you got something interesting for me.

[SpeedsterBek]

Wow that's fuel economy sucks. My 525i gets about 11l/ 100km (21-22 MPG) with mixed driving but I drive hard.
Anyway we need more info like :
-what was the previous fuel mileage numbers
-it's auto or manual,
-what kind of gas you're putting
-what kind of tires and wheels you're running and what KPA (or PSI)
-whether you're calculating fuel economy by hand or relying on OBC,
-when was the fuel filter was changed

It might sound so simple, but try cheaper things first like check tire pressures, check your brakes whether they are dragging, try premium gas, replace fuel filter.
Hope that helps

[arnoldmatusz]

Hello SpeedsterBek

First of all I would like to thank you for your reply!

1) I've done the engine service around 8500km ago when I've changed the following: Castrol 10W/40 Oil, air filter, fuel filter, NGK spark plugs
2) all wheels turn freely and easy (including the rear ones - but of course there's a bit of resistance due to the differential) - but there are definitely no sticking breaks
3) It's manual (and interestingly it doens't care if I change gear at 1500RPM or 2500 RPM or 4000 RPM). ( I have the car for half a year now and drove around 12000km's and it's fuel economy has been the same from start). I was really hoping that the O2 sensor would solve it.
4) I'm putting in 98 octane gas - (although it says it would be sufficient to fill up with 95).
5) My wheels are 195/65/15", with the following pressures (and I checked this several times), 2.2 bar front, 2.5 back (31.9 psi front, 36 psi back)
6) I'm calculating fuel economy by hand. EXPLICITELY: noting down numbers on my speedo when I'm filling up)

It's been having this fuel consumption since I had it and asking the previous owner won't help (because he might have sold the car right because of this).

Thanks again.

[SpeedsterBek]

Are you getting any codes?
What about coil packs, does all cylinders fire up?
Sorry I am stuck as I don't know what else could be affecting mileage

[arnoldmatusz]

Yes sir, I've mentioned that above, I did change the fuel filter!
Well ... considering it's got only 8500 km it shouldn't be "used" ... and it did the same mileage per gallon even before it was changed. I can't imagine it is the fuel filter.

[attack eagle]

did you put the filter in the right way? no vacuum leak at the brake booster? coolant temp sensor for the ECU (not the gauge) is ok? maf is clean? boot is not cracked?

I get about 14 around town and 24-26 freeway for an average of 18-19 on my morning commute.

probably time for a compresssion and leakdown test... a 520 = abused engine... period. It is too small for the load so it is caned as a matter of necessity.

[arnoldmatusz]

Are you getting any codes?
What about coil packs, does all cylinders fire up?
Sorry I am stuck as I don't know what else could be affecting mileage

Codes? I've been to a diagnosys around 1.5 months ago when I got the fault for the O2 sensor which I've replace with a completely new one!

All cylinders seem to fire up well (the engine runs pretty smooth, there are no missfires) and I've also took the spark plugs out, and it seems that there's no oil consumption, all spark plugs had that reddish color (black-to-red) indicating a good combustion.

The only problem I can notice is that it doesn't pull very hard in low revs, but as far as I'm aware of this is somehow the same for all m50 owners (they only seem to pull hard after 3000-3500 revs).

Once again the diagnosys didn't show any other errors!
How can I check if my coils are ok?

did you put the filter in the right way? no vacuum leak at the brake booster? coolant temp sensor for the ECU (not the gauge) is ok? maf is clean? boot is not cracked?

I get about 14 around town and 24-26 freeway for an average of 18-19 on my morning commute.

probably time for a compresssion and leakdown test... a 520 = abused engine... period. It is too small for the load so it is caned as a matter of necessity.

Yes sir, the filter is the right way on! There is no vacuum leak anywhere, I've checked and rechecked that!
Shouldn't the Coolant temp sensor throw and error which should be read by a tester?
MAF has been off, I cleaned it!
Boot was cracked ... has been changed ... no noticeable performance/consumption change.

Thanks for your answer. I've looked after my problem on the internet for anu clues but sadly I couldn't find anything until now.

[DIL]

Maybe try a can of injector cleaner?

[arnoldmatusz]

Hey

Thanks for your reply!
I really hate to be a "smarta$$" to say I've done everything.
This may also be a reminder for me to check and recheck everything coz I know it's not right like that. An M50B20 shouldn't have a fuel consumption like this.

I've tried a fuel injector cleaner, a more "expensive" one from Liqui Moly. (Of course this is something you pour into the petrol tank). Specialists told me there is no use taking them off and cleaning them off from the engine because all the spark plugs are clean, indicating that the petrol reaching the chamber is in a nice vapour format!

Thanks again for your idea!

[5mall5nail5]

Tough call - check for a clogged catalytic?

[arnoldmatusz]

Hello

Thanks for your reply!

No I haven't checked that! I'm sorry for a very lame questions but I would like to ask how I can do that?
How can I check if the cathalitic converter is clogged up? I mean if I take the rear and front silencer down looking into it won't help allot. Once again ... sorry for a lame question!

See this is why I posted my question here, asking questions of any kind may help and I appreciate each and every reply anybody sends.
Thanks allot guys!

[moroza]

It sounds like it's putting down all the power it's supposed to...so I'd guess it's running rich? I don't know what kind of emissions standards or testing exist in Romania, but if you can find some place to measure HC and CO output, I'd go there and see if it's dumping fuel.

[attack eagle]

all spark plugs had that reddish color (black-to-red) indicating a good combustion.


There is no vacuum leak anywhere, I've checked and rechecked that!


Shouldn't the Coolant temp sensor throw and error which should be read by a tester?

Spark plugs should be tan, not reddish/black


There is a check valve on the brake booster hose. on the underneath side you should have a spare nipple which is capped off... Often that nipple just breaks off... Almost everyone I have ever seen has been broken off and has a vacuum leak there.

Coolant temp sensor: not if it is just 'somewhat off' and not failed open. Especially on PBDI cars. That'll keep the car in warm up and out of closed loop, IE rich.
Spark plugs should be tan, not reddish/black

Which exact plugs are you using???

[arnoldmatusz]

It sounds like it's putting down all the power it's supposed to...so I'd guess it's running rich? I don't know what kind of emissions standards or testing exist in Romania, but if you can find some place to measure HC and CO output, I'd go there and see if it's dumping fuel.

Hello, thanks for your reply!
I was thinking about this, but it has recently been to the "MOT" the mandatory periodic inspection at the national authority, where it passed. As far as I'm aware of they are testing CO emissions. But sadly I don't know any numbers, so I'll have to take it to another emissions test.
Thanks for your idea!

Spark plugs should be tan, not reddish/black

Hmm, sorry, maybe my "way of expressing what I've seen is off". The mechanic said it's good. They were clean, no oil, not wet at all!

There is a check valve on the brake booster hose. on the underneath side you should have a spare nipple which is capped off... Often that nipple just breaks off... Almost everyone I have ever seen has been broken off and has a vacuum leak there.

Can you please tell me which item you refer to? (a realoem part number for a november/92' 520i manual, sedan, m50. Sorry I can't post links!

Which exact plugs are you using???

I'm using standard series NGK Spark Plugs, the part number I can find on the net is: NG2288. These spark plugs have 2 poles! (they were far more expensive here than the stupid 4 plug turkish BOSCH's). But anyway the behaviour didn't change at all when I changed the Bosch's to the new NGK's.
I've driven the car around 4000km (most of this outside the city at 100-120km/h), and I got 11-12l/100km fuel consumption, which I don't think is acceptable, considering it's not a huge V8.

Thanks for your replies guys! I appreciate it allot!

[bjkbarann]

Hello, I followed the topic. How did you do the solution?

[shogun]

you will not get a reply, he was last time active here in 2008.
Use a fault code reader for your car, your Euro E34 does not have stomp test fault code reading.
Which E34 do you have? Not enough info

My Cars E34

engine, built year/month, automatic or manual transmission? What is the exact problem? Which maintenance has been made to engine wear parts ? What has been tested? Such as air temperature sensor, coolant temp sensor, O2 sensor(s), changed distributor, rotor, ignition coil, total km etc pp?

[bjkbarann]

thanks for your reply, i tried code reader but i couldn't connect. The weather is cold for 2 months and I have an average of 20lt / 100km. I didn't have such a problem when the weather was hot. I had a 9-13lt/100km average when it was hot. But now I drive the car for only 10 km and park it, and I turn it off before my car reaches 90 degrees at 10 km. My air filter, oil, coils, spark plugs have been checked. I use BKR6EQUP as spark plug. I also had an exhaust test, my CO and Lambda values were high at 4000 rpm. Lambda 1.04 (0.97-1.03) , CO 0.64<0.30 . I tested the vacuum leaks with the lining spray while the car was running. it looks like no.

[bjkbarann]

Hello everyone,

my e34 95model,520İA 395.000km.the acceleration torque is fine and fresh, I don't know if the engine has been made before.

i tried code reader but i couldn't connect. The weather is cold for 2 months and I have an average of 20lt / 100km. I didn't have such a problem when the weather was hot. I had a 9-13lt/100km average when it was hot. But now I drive the car for only 10 km and park it, and I turn it off before my car reaches 90 degrees at 10 km. My air filter, oil, coils, spark plugs have been checked. I use BKR6EQUP as spark plug. I also had an exhaust test, my CO and Lambda values were high at 4000 rpm. Lambda 1.04 (0.97-1.03) , CO 0.64<0.30 . I tested the vacuum leaks with the lining spray while the car was running. it looks like no.

Thank you to the friends who helped.

[shogun]

when you drive only 10 Km = abt 6 miles, then engine does not reach operating temperature most of the time. In addition as you have a automatic transmission, the trans will shift later to the next higher gear, that is to reach operating temperature as soon as possible. Higher RPM caused by this = more fuel consumption.
The Motronic ECU contains a fuel map with an injector opening time for basic conditions of speed and load. Information is then gathered from engine sensors such as the AFS, CAS, CTS, and TS. As a result of this information, the ECU will look-up the correct injector pulse duration right across the engine rpm, load and temperature range. The Motronic multi-point injection system pulses the injectors semi-sequentially and once every two engine revolutions. During engine start-up below 600 rpm the ECU pulses all injectors simultaneously. Once 600 rpm has been attained and if the ECU has received a signal from the CID sensor, each injector bank will be pulsed alternatively according to which pair of cylinders are approaching TDC. If a signal is not received from the CID sensor the injectors will remain on simultaneous operation. However, if the CID sensor subsequently sends a signal to the ECU after the engine has commenced running, the ECU will pulse the injectors semi-sequentially after the next deceleration phase - even if the CID sensor then ceases to send a signal. During start-up from cold, injector pulse duration is increased to provide a richer air/fuel mixture and pulse frequency is also increased. In addition, the ignition timing is also retarded. Injector frequency & pulse duration and degree of timing retard depend upon the engine temperature both during start-up and immediately afterwards. If the engine is restarted within one minute of the first start occurance, less overall fuel is injected to reduce the risk of fuel flooding into the engine.

Air Flow Sensor (AFS)
From the voltage returned, the ECU is able to calculate the volume of air (load) entering the engine and this is used to calculate the main fuel injection duration. The AFS exerts a major influence on the amount of fuel injected.

test the coolant sensor and airflow sensor. Lambda 1.04 (0.97-1.03) , CO 0.64<0.30 is high . When did you last time change the Lambda sensor? When they get old, the react slower.
#13 air sensor http://bmwfans.info/parts-catalog/E3...nifold_system/
#13 coolant sensor http://bmwfans.info/parts-catalog/E3...nos#1747281_13
#15 is the coolant sensor for the temperature gauge in the cluster , but that is not connected to the DME

NTC sensor testing http://www.e32-schrauber.de/bmw/date...u-2_5-kohm.png
2.5 kohm at 20 degree Celsius

[bjkbarann]

Thank you for your early comeback, I'll write back after doing what you said