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Old 04-14-2013, 08:51 AM   #1
Andrew S
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poor fuel ecomony - any ideas why?

Hi all,

I'm reaching a dead end with trying to find out why my car seems to be using too much fuel...and hope someone on here can advise me on what could be causing it.

Firstly my car is a UK model 1995 E36 2.0 with the M52 (6cyl) petrol engine, with vanos on the intake manifold. The engine has covered 170,000 miles but runs well and I've changed the oil every 4k, it also has good compressions on all cyclinders, although a little slow to build.

The car ticks over fine, heats up fine (needle sits bang in the middle) although the viscous fan never cuts in if it does get too hot.

The car is returning around 22mpg round town and the co2 level is around 0.6 (should be below 0.3). Consumption has been getting worse for some time (I posted about some time ago:http://forum.e46fanatics.com/showthr...939&highlight=)

Within the last 2 years I've:

had the original injectors serviced and replaced
fitted new o2 sensors

In the last few months I've:
fitted a new cat
new air recirc valve (back of throttle body)
service (inc new fuel filter and air filter)
used fuel cleaner and given it a good run to get the emissions down

....none of this has made a difference and the car seems to be running rich.

the only bits I can think of left to swap are:
air flow sensor
air temp sensor
engine temp sensor
crank pos sensor
cam pos sensor
ecu
fuel return valve

...problem is the car isn't returning any fault codes, so I'm kinda scrabbling in the dark to find the fault. To me it seems like the car is constantly running in cold start mode or similar, but i'm not sure which sensor would cause this or even if it has this mode to run in as a programme.

Any ideas?
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Old 04-14-2013, 09:01 AM   #2
dmax
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Replace your thermostat.

I'd bet that if you ran on the highway for 10-15 mins. you'd see your temp gauge run just a little to the left of dead center. In town, the speed doesn't generate that much cooling in the radiator, but it's still sitting low on the edge of operating temp. You won't get a light on the cluster, though you might have a stored code.

But, many of the sensors you suggested would show a code, so rule all those out...maf, cps(s), temp gauges...they'd send a code, guaranteed.
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Old 04-14-2013, 09:05 AM   #3
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This.^
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Old 04-14-2013, 09:09 AM   #4
Andrew S
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Thanks, will give it a try. I last replaced it at 132,000 in 2008. Would this sticking cause poor economy? Are you suggesting it's sticking closed?

Worth adding I've done less motorway/highway miles in the last few years and have mostly used the car for shorter journeys.

edit: sorry, realised what you're saying is that it's sticking open, causing a longer warm up.

Last edited by Andrew S; 04-14-2013 at 09:30 AM.
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Old 04-14-2013, 09:29 AM   #5
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They fail open causing the engine to run too cold.
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Old 04-14-2013, 10:29 AM   #6
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 04-14-2013, 11:12 AM   #7
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22 around town? What's wrong with that? My '94 'vert does that on the highway, at 70+ with the top down.
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Old 04-14-2013, 12:22 PM   #8
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Quote:
Originally Posted by jdstrickland View Post
22 around town? What's wrong with that? My '94 'vert does that on the highway, at 70+ with the top down.
^^^Agreed. 22mpg around town is really not that bad. Manual or auto tranny? Short trips especially in cold weather is not good long term unless you regularly take it out on the freeway at freeway speeds for 30 minutes at a time. If you can use your OBD to check coolant temps, do so and report back.

If your freeway/city-stop-n-go ratio changes to favor freeway driving more like mine (70/30), then you should expect mpg at least in the high 20s or maybe a little higher.
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Old 04-14-2013, 12:23 PM   #9
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Old 04-14-2013, 12:27 PM   #10
Andrew S
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Thanks jfoj, very useful. Hopefully I'll be able to see the OBC menu on mine (which is an e36), so see the actual engine temp.

jdstrickland: I used to get 28mpg! I'm now getting only 22 despite making the kids walk alongside the car (and push it up hill). Will rpt back post new temp thermostat. Cheers guys, can't thank you enough.
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Old 04-14-2013, 12:32 PM   #11
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AndrewS,

What kind of fuel are they using in the UK now?

Are they using a 10% Ethanol blend fuel which at this point is very common here in the US?
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299

Last edited by jfoj; 04-14-2013 at 12:43 PM.
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Old 04-14-2013, 01:08 PM   #12
Andrew S
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not sure tbh, as they don't give you much info other than the octane rating at the pump. it's all bloody expensive though! fuel prices going crazy over here, hence diesel cars are on the rise
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Old 04-14-2013, 01:14 PM   #13
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Unfortunately the European fuel costs are driving mostly by taxes that are used to subsidize public transportation and pay for roadway maintenance.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 04-14-2013, 01:19 PM   #14
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I'm with dmax on this thermostat
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Old 04-14-2013, 03:57 PM   #15
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Quote:
Originally Posted by Bnutz29 View Post
I'm with dmax on this thermostat
Easy test...head out on a country road and keep it at 40-50 mph for 10 mins...

Maybe hunt for some illegal stilton cheese!
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Old 04-14-2013, 05:43 PM   #16
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We do get higher octane at least, 95 is standard and 97-98 is premium I use Shell V-Power, I'll look it up later. Taxes are iirc at least 70% of cost.
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