E39 525i - Heavy fuel consumption

[clinton76]

Hi Guys,
I have a problem with heavy fuel consumption on my 525i. I have had the faults read and it showed a problem with the Vanos on the exhaust side. I have since replaced the entire unit and the faults came up with an all clear. The Vanos swop has made a slight improvement but not that much. The timing was also checked and its spot on. My question is this : Will changing the spark plugs and oxygen sensors make any difference to the fuel economy if they are not currently showing up as an error? I cant seem to get the consumption down to less than 16L/100km. is this normal? is there anything else i could check that may be causing this, like leaky air hoses or dirty maf? Also, has anyone chiptuned an E39 525i? does it make a difference to the economy and are there any reputable companies in Cape town i could call? thanks guys for all your help.

Ragards
Clinton
:=):

 

[maximus]

-Check your tire pressure, I know it may seem stupid but just check them

-As for cleaning the MAF sensor, I'd recommend using a proper MAF cleaner (MiniMike on the forum should still have some LiquiMoly cleaners left for about R70).

-If things still haven't improved, maybe it's your driving style? :dunno: :rollsmile:

 

[moranor@axis]

that consumption is no where near normal the most you should get is 12l/100km...

DONT tune a car that has other problems...

clean maf, take covers off and look for vacuum leaks... then look at maybe doing O2 sensors but they should bring up codes?

how does the car drive?

 

[Nic_s]

When was the last time the car had a good service? New Filters ect?

 

[Sabretooth tiger]

+1 on the service, full service including spark plugs. And check for vacuum leaks.

 

[whattingh]

I would say start with service with new oil air and oil filter an sparkplugs

Like they said check for air leaks.

Also bit of a longshot, maybe bad cat? Maybe got bad fuel somewhere that messed up the cat..? blockage..

just putting ideas out here

 

[Sabretooth tiger]

decat should make a huge difference

 

[Raybimmer]

dirty or clogged air filter will make a big difference .
o2 sensor ? I would expect a fault code to show up - you can disconnect one and then do diagnostics and see what code comes up .
Does the car have the same performance as usual ? Any more induction noise etc . Check for leaking pipes , eg your vacuum hose(s) from the brake booster to the inlet manifold .
Does the car idle ok ?
What was the consumption before ?

 

[clinton76]

i have the car for about 3 months now. It was heavy on fuel from day one. What promted me to take he car for fault reading was because there was a very slight rattle coming from the front. My Mechanic hooked up the fault reader and the vanos problem came up on the exhaust side. Like i said i had this replaced and the noise disappeared along with the fault code but the consumption improved just a little. If i de cat the car, will this mess around with the obd? Will i have to get the fuel map reset? or will the car adjust itself? has anyone done a decat before? Pro's vs cons vs cost??? I think i'm going to do a full service this weekend even though the previous owner said the car had one around about the time i bought it. i have also noticed alot of of sludge build up in the tappet cover and i'm thinking maybe the garage that did the previous service put in multigrade oil instead of fully synthetic. i think i will put my suspicions to rest and do the service again to give me peace of mind.

---

oh, and the other morning i started the car and it felt as if it was firing on 5 cylinders. i drove it for about 1km before turning around and heading back home. when i turned off the ignition and restarted the car was fine. could this be a sign that the plugs are on their way out? could bad plugs mess with fuel consumption?

 

[whattingh]

Do a search on the forum for decat. plenty of info around. IIRC my E39 525 only has pre cat sensor but a decat should not effect it.

Make sure you have the correct plugs in. Once got a car and was not running well which turn out previous owner was cheap ass and put wrong plugs in.

Best place to start I think is :
- Check if the car has the correct plugs in and their condition. Lot can be said from the state of plugs. ( easy if you have plugs socket)
- Check or maybe just replace air filter, cheap enough item. (dead easy job)
- Check how oil looks on dip stick. If replaced just before you got the car it should not be black already i think. ( easy job)

just my 2c

 

[Raybimmer]

+1

 

[clinton76]

okay guys, it's Monday morning and i'm happy to say i went to town with the service on my girl. After a call to MiniMike he pointed me in the right direction wrt all necessary oils etc from SOS oils in Observatory. Really astonishingly cheap prices! All liqui moly products........ from the engine flush to the valve cleaner (Liqui Moly Valve Clean) to the oil additive (Liqui Moly MOS2 Antifriction Engine Treatment 300) and obviously the oil (Liqui Moly Longtime High Tech 5w30 005) ......all 6.5 litres of it. I also got a can of their MAF sensor cleaner and changed the 2 pronged champion plugs (they looked fine to me. Slightly brownish creamy colour but with a bit of deposit) for 4 pronged Ngk platinum jobs along with the oil filter element. The air filter looked new so i didn't change that. the car seems much more responsive and idles much smoother than before. So now i guess i will have to monitor the consumption. i will report back at the end of the week, hopefully with some good results. thanks for all the advice so far guys, much appreciated.

Regards

Clinton:=):

 

[Raybimmer]

Good luck , hope she is going to reduce her appetite .:thumbs:

 

[sclass]

Is it a good idea to flush an engine which has extended mileage? Does that not open the door for other problems (like smoking)?