Garbage Fuel Economy

[Chr!S]

I have a small mystery - CG10DE micra cannot better 25-28 MPG!!!

I have checked the usual like brakes binding / smoke / given it a full service etc...

The thing is that with no smoke and no rough running it seems to have the correct mixture, yet the car is using MORE fuel than my last car. I bought the micra to run around instead of my Carina GTi but the Carina uses the same fuel and has 1220 KGs to haul + university stuff in the boot + A yamaha 3SGE in the front...

The only thing I can think of is that the timing may be miles out as the chain/tensioners are worn, but the rest of the car appears healthy...

Can anyone see what is wrong?

 

[TredderK11]

Have you checked simple things like tyre pressure and also how heavy your right foot is lol

 

[rlees85]

thats poor mpg even for a ragged cg10de. check o2 sensor, maf sensor, etc

 

[sonic]

give it a good service, filters, fluids and plugs, also check the tyre pressures are correct, also try using a different petrol supplier, fuel differs from supplier to supplier.

 

[Chr!S]

As in my previous post I gave it a good service with all the filters and a new maf and throttle body ect... Tyre pressures are ok.

Haven't checked the oxygen sensor, I will have to check it. Anyone know the voltage range or what I should be looking for?

Economy seemed better last night using the same petrol station. I have had a few problems with the texaco station lately but the poor MPG seems to be consistent across different suppliers (went on a road trip through plymouth and dartmouth yesterday about a 120 mile round trip).

The actual wiring and plug looks suspiciously clean which led me to believe it was recent on the car, but also some of the little faults on the car were "repaired" in the service history. Something's not quite right here....

 

[ollyc98]

If the oxygen sensor was replaced with a cheaper one you would lose economy, you really need a Nissan one.
There isn't a 'piggy back' ECU somewhere is there? Some people rip apart the ECU to solder on resistors, like idiots and it would explain some stuff...

 

[Chr!S]

*Update*

It decided not to start one morning what-so-ever. This resulted in the ECU being switched for another one and now its perfect...

However, every now and then it seems to be very rich still (and subsequently burning fuel). I have noticed that the exhaust tip has now silvered instead of being black, which is a step in the right direction.

Where is the mixture adjustment (if there is one) and roughly speaking what should it be set to? I havent really pulled the CG apart or had time to search for it yet

The micra ECU I removed was standard... Probably not matched to the throttle body. The one I put on (from a UK 1.0 LX) had a different Part number to the OE one (from my JDM) as did the ECU.

Maybe if I fixed the idle valve in the old ECU they would work as a pair if anyone needs a replacement set..

It was actually my father that installed the new TB, he said something about "a" and "b" being on the two different parts..

Anyone know of this?