Poor MPG

Lloydt · Dec 12, 2012

Hi all,

I’ve borrowed my mums 55 plate, 1.2l for a while. 65k on clock. MPG seems to be really poor. Getting 60miles per £10. Driving really slow doesn’t seem to change it much.

To be honest it hasn’t has a service in a while. I changed oil, filter and air filter. I’ve let that bed in for a month, still no change. Any ideas?

Also gears have got noticeable more clunky/notchy over the past 6months. Seems plenty left on clutch. Have noticed lately, if car is in gear and you fully press clutch in it sounds like its still engaged if you get what I mean. Any ideas??

Jen319 · Dec 12, 2012

I find that my MPG suffers at this time of year
...engine takes longer to warm up and you've got the blowers going hot all the time..I guess that could possibly be part of it?

I'm not sure about the clutch/gear changing being clunky? might be an idea to have that looked at if it's worrying you...
If you're mum had a tendancy to sit on the clutch?...might not help?

When i first got my K12 i didn't get great MPG (55 ish instead of 65, she's a diesel ) I had the Pollen/cabin filter changed, the old one was all horrible, and my MPG got so much better...and my A/C worked loads better too...might be worth changing that too?

pollyp · Dec 12, 2012

get the sensors checked over with diagnosic software.
could be faulty O2 sensor or coolant temp sensor causing rich mixtures. binding brakes.

the high energy demands of winter always guaranteed to reduce mpg

Lloydt · Dec 14, 2012

Cheers its been like it through summer as well not just winter. Wasn't till I checked the miles I realised how bad it was.

I've checked the brakes, they are fine not binding, put on a obd2 reader and no codes came up.

pollyp · Dec 14, 2012

i think a slightly sluggish o2 may not bring up a code. ya need some way to monitor the reading response of the o2, if its oscilating up down fast enough at 2k rpm

Lloydt · Dec 14, 2012

Whats the best way forward? Put it into a garage to test it? don't really want to splash out £60 and still be in same postion.

frank · Dec 14, 2012

you can test the lambda with a volt meter on the middle wire lloyd, it should bounce between about .3v and .6v @ cruise, about .9v @ full throttle, and 0v on lift

pollyp · Dec 14, 2012

imho I'd buy myself a usb consult cable and nissan datascan license to keep forever which is an invaluable tool in the long run for future self diagnostic.
u can buy the consult cable first (£62), download & try the datascan trail run free to see if it works with ur ecu. if it connects n displays basic readings then you can register for a datascan license (£32) to unlock all the software features

datascan link
http://www.nissandatascan.com/

plms who can supply the cable & software
http://www.plmsdevelopments.com/consult_if.shtml

Lloydt · Dec 17, 2012

frank said:
you can test the lambda with a volt meter on the middle wire lloyd, it should bounce between about .3v and .6v @ cruise, about .9v @ full throttle, and 0v on lift

Thanks, if its gone will it read zero? cheers

Lloydt · Dec 17, 2012

pollyp said:
imho I'd buy myself a usb consult cable and nissan datascan license to keep forever which is an invaluable tool in the long run for future self diagnostic.
u can buy the consult cable first (£62), download & try the datascan trail run free to see if it works with ur ecu. if it connects n displays basic readings then you can register for a datascan license (£32) to unlock all the software features

datascan link
http://www.nissandatascan.com/

plms who can supply the cable & software
http://www.plmsdevelopments.com/consult_if.shtml

Thanks but thats abit more than I plan on spending as its not my car and its not going to be kept for that long..

frank · Dec 17, 2012

Lloydt said:
Thanks, if its gone will it read zero? cheers

they can go very sluggish lloyd, but i guess they give no reading when failed

col85 · Dec 17, 2012

The 55reg K12 is the facelifted one and these have quite a common fault of corrosion getting into the downstream (After Cat) Lambda Sensor Connector (but often cant be seen even when plug disconnected) This causes over fueling and poor MPG.
An easy way to test for this is to probe the Upstream (Befor Cat) Lambda Sensor just as Frank has demonstrated, with the engine warmed up and the car stationary when you rev up engine check the voltage doesn't go above 1Volt (it shouldn't go below 0.01Volts or above 0.99Volts)
If it does get above 1Volt, try dissconnecting the Downstream Lambda and re-checking Voltages on the Upstream one. If the Voltages then stay within spec the Downstream Sensor is the problem. Clean connections and replace Sensor get code erased and it should be all good.
(the Down stream sensor confuses the ECU which make the Engine fuel wrong which causes the over rich voltages from the Upstream Sensor) I know this sounds odd but its is very common. Hope this helps.

Lloydt · Dec 18, 2012

Thanks, Will order an multimeter now.

Poor MPG

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