Poor Fuel Economy

[CMF_klockwork]

I have a 1998 K11 Nissan Micra 1.0L which has about 65000 miles on the clock. I don't have any service history so I do not know what work has been done on it. Recently it has started to give me less and less miles per gallon. The last time I filled it with 20 litres of fuel it gave me about 130 motorway miles, which as far as I know is way below what it should be giving. I have changed the air filter and spark plugs but this has made no difference. I have also noticed that the exhaust fumes have a very chemically smell which I am told by a friend is that of unburnt or partially burnt fuel. There is no steam coming out of the exhaust and the car never has water dripping from the exhaust. I am aware that with these ECU controlled engines there are many sensors and if any of them are defective then this can lead to poor engine function and poor fuel economy, I was told that the most common fault is with the lambda sensor. However this costs about £120 in the UK plus fitting costs so I am reluctant to change it without knowing for sure that it is the problem. I am wondering if anyone has had this same problem with their Micra or has any ideas on how I can find out where the fault lies. I would be grateful for any help. Thanks

 

[CMF_frank2]

klockwork

you could test the lambda with a voltmeter (+ to the middle wire), it should read about .5v with no engine load, and if the coolant sensor has failed, i think it would overfuel

frank

 

[CMF_klockwork]

Hi frank2,

So I do this with the ignition on but the engine off, or does it not matter? Is there any way of testing the coolant sensor that you know of?

Thanks

 

[CMF_frank2]

klockwork

its best to put the meter on the dash and drive the car (you,ll have to run a lead to it tho eh)
not sure on the coolant jobbie, resistance check when cold and hot ? (there are maybe 2 under the dizzy iirc)

frank

 

[CMF_asdame]

i got my lambda sensor from a local Partco shop for 50 quid. when the sensor goes, no signal is sent to the ecu and makes it run on rich fuel mixture which may explain ur bad consumption and exhaust smell.

i'd get a sensor from partco n fit it urself.
dead easy, simply unplug the sensor and unscrew the sensor off the manifold with a big spanner or adjustable one. new sensor should already have a dab of grease on the threads.

btw another way of checkin if the sensor is working (warm engine up first) is by shorting the bottom left two pins of the diagnostic plug below the fusebox for two secs with the ignition on and engine off, this sets the ecu on diagnostic mode. the dashboard engine light flashes with several long pulses then short pulses, these are the diagnostic morse codes.

now to check the lambda sensors workin, start the engine and hold it at 2000rpm. the engine light now represents what the ecu is receiving from the lamda sensor.
engine light on means a lean exhaust gas mixture.
engine light off means a rich exhaust gas mixture.
it should pulse on & off on at least 1/2 sec intervals. if not, then the sensor needs replacin.

switch off engine to return ecu back to normal mode.

 

[CMF_klockwork]

I shall give those suggestions a go. is there anyway of testing the coolant sensor to see if it is working or not? It appears to be working because when the engine warms up the engine speed drops back down again and the automatic choke appears to go off. Thanks again

 

[CMF_asdame]

there are two temperature sensors on the cylinder heads left side aparantly, dunno why nissan did this. one is for the ecu, and the other smaller one is for the dashboard temp gauge.

haynes manual suggests you could unscrew it out to test (bung the hole to keep in coolant), dip it in hot water monitored with a thermometer and connect a multimeter across the pins to read the resistance. As temperature falls the resistance should increase with specification.

 

[CMF_Stallion]

also check the trottle potentiometer senser located on the trottle body on the left side looking from the front of the car hook the multimeter on the first terminal looking from the front of the car and middle terminal at trottle close it should read .5kohm if not loosen the screws and ajust till it reads right

 

[CMF_klockwork]

I changed the lambda sensor myself today and the car seems to be running slightly better. It has stopped producing the foul smelling smoke that it was doing before. I am yet to find out if the fuel economy has increased as I have not had a chance to properly drive the car.

 

[CMF_klockwork]

Fuel economy has improved dramatically since I changed the sensor. I would reccomend that anone having poor fuel economy check thier lambda sensor becuase, if that is the problem, it can be very easy to fix.

 

[CMF_asdame]

nice one

 

[CMF_klockwork]

Thanks, and also thanks for the advice asdame

 

[CMF_qwerty132]

Hey,
Im having similar problems... My car uses at best 6l/100km cruising long distance on the highway and way more around town.. Its starting to annoy me as I bought this car because I wanted a car that was really good on fuel...

Anyway, Can someone tell me which temp sensor Is the one the that ECU reads?? My dash gauge is fine. I think there is a 3 wire one and a 2 wire one. Which do I need to replace?

Thanks
qwerty132

 

[CMF_Micra_King]

Dont you mean you need to replace the O2 sensor? lambda sensor is an O2 sensor in case other did not know. I was getting around the same figures but since replacing mine last week im already knoticing a difference and the fuel smell I used to get is also gone. I am getting in O2 sensors and selling them cheap if you want to replace yours.
https://micra.org.uk/cmf/message/35520

 

[CMF_qwerty132]

Hey,
I have checked the O2(lambda) sensor both with a multimeter and also with the shorting the pins on the ecu to get to the diagnostics mode..
It seems to be fine... Im going to resolder the throttle body and then maybe look at replacing the coolant sensor for the ecu first...

I dont really have the money to swap the O2 sensor unless its obviously dead at the moment.. Resoldering costs basically nothing and I dont think the coolant sensor would cost that much would it? I figure I may as well do it when I replace the coolant anyway..

Thanks
qwerty132

 

[CMF_klockwork]

The lambda sensor which was dead read just under 0.2v from what I remember. Apparantly it should read between 0.2v and 0.8v if it is working fine.

 

[CMF_uhkoo]

i having the same problem with my micra (march. it burns around 8 l/km. is it normal? should i be checking my car´s lambda sensor?

 

[CMF_asdame]

uhkoo
you do mean 8L per 100km right? (29.45mpg, which is bout my urban driving range if i constantly kane it)

cos 8L per 1km that you typed is only 0.29mpg (bout as good as a fuel tank with holes)

doesn't hurt to try n check the sensor via the method i mentioned