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Awful Fuel Consumption

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TomMan7531
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Location: Southampton, Hampshire, UK

Awful Fuel Consumption

Post by TomMan7531 » Thu May 24, 2018 9:46 pm

So its taken a year of me owning the car but I've just worked out i'm getting about 12mpg out of my pre august 87 635csi with no catalytic converter ](*,)

I've heard the oxygen sensors can be the first thing to look at as the car has done over 100k miles but where would I find it as cant find it on real OEM??

To be fair I've always thought the car ran rich from the smell but I just thought that was the old car charm :lol:
1987 BMW 635CSI Auto, Royal Blue, Cream interior, daily rust finds....

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Hefeweizen
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Awful Fuel Consumption

Post by Hefeweizen » Thu May 24, 2018 10:44 pm

We had a similar problem with my son's 633 where one or more injectors were stuck in the open position. 12Mpg is definitely not a good one considering I am averaging 22mpg. See if you listen to your injectors clicking (either get a mechanic's stethoscope or use a long screw driver while the engine is running).
Rainer
85 635CSi (Silver, Daily Driver)
79 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"

ron
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Re: Awful Fuel Consumption

Post by ron » Fri May 25, 2018 6:26 am

TomMan7531 wrote:
Thu May 24, 2018 9:46 pm
I've heard the oxygen sensors can be the first thing to look at as the car has done over 100k miles but where would I find it as cant find it on real OEM??
You won't find them on a UK car.
They are ALWAYS rustier than you thought!!!!!!
'88 High line.
'85 M #228
'85 M #207
'80 735i

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wattsmonkey
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Re: Awful Fuel Consumption

Post by wattsmonkey » Fri May 25, 2018 7:05 am

At the risk of making a sucking eggs point, it's a big engine that takes a fair while to warm up, so lots of short runs will have a drastic effect on fuel consumption.

I get 200 miles out of a tank in mixed driving with the M; I got at least 250 out of the 635.

I did think that the Highline's B35 set up was supposed to be more economical, even given the extra weight, plus the newer motronic does away with the cold start injector iirc.

Anyway, getting the injectors cleaned is definitely a good shout and don't forget that the Imperial UK gallon ain't the same as the US one, they do things bigger over there!
"Most of it necessary; all of it enjoyable[!]" LJKS
'86 M635CSi #367 Bring the Noise.
'84 635CSi, dogleg fun

ron
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Re: Awful Fuel Consumption

Post by ron » Fri May 25, 2018 7:12 am

wattsmonkey wrote:
Fri May 25, 2018 7:05 am

....don't forget that the Imperial UK gallon ain't the same as the US one, they do things bigger over there!
Surely "smaller"!!
They are ALWAYS rustier than you thought!!!!!!
'88 High line.
'85 M #228
'85 M #207
'80 735i

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wattsmonkey
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Re: Awful Fuel Consumption

Post by wattsmonkey » Fri May 25, 2018 7:16 am

Damn that maths!
"Most of it necessary; all of it enjoyable[!]" LJKS
'86 M635CSi #367 Bring the Noise.
'84 635CSi, dogleg fun

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TomMan7531
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Re: Awful Fuel Consumption

Post by TomMan7531 » Fri May 25, 2018 10:41 am

Ill try and look at the clogged injector route. TIme for maths

80 quids worth of fuel at £1.28 per littre (love the UK) that works out at 63 liters (13.8 gallons) which has got me 160 miles

11.6 Miles to the gallon \:D/ \:D/ \:D/ \:D/
1987 BMW 635CSI Auto, Royal Blue, Cream interior, daily rust finds....

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