Bad Fuel Economy

[PUDZ 32R]

if your fan clutch is screwed it will be locked on even when the engine is warming up. you can tell this by getting under the bonnet and revving the engine. if the fan makes a massive roaring noise so you can hardly hear the motor for more than a few seconds at a time (providing the engine is not very hot) check it on a cold day. if the fan roars for a few seconds and turns off it is working fine. mine locked on in my 31 i used2 own and the motor had f**k all power and chewed the fuel. those fans pump a shitload of air and take about 30hp out at 5000rpm.

also like many others have said you should sit in fourth or third. labouring the car will make it use more fuel as the engine is trying to boost even tho the guage says its not so the injectors are pumping shitloads of juice in in an attempt to get more revs when you touch the throttle even a tiny bit. but it will respond slow and chew juice. hope this helps.

do you stil run an the AFMs or is it running in D-Jetro mode with MAP sensors?

[ian]

as per the post above - with the engine rpm increasing it just gets noisier!

Ian

[paulr33]

hello

what causes bad fuel economy?

constantly loading the engine up

constantly loading the engine up & bringing it on boost

poor state of tune

failed 02 sensors

02 sensor closed loop turned off

poor throttle control

bad setup injection control

based on what ive seen and read in here i would check 02 feedback is turned on in the hand controller

this is covered in the PFC FAQ (in my signature) check that first, it should be ON by default.

has the tuner tuned your light cruise cells with a wideband sensor?

don't assume this has been done, not all tuners do it, some only do it when you ask

without this light cruise tuning the fuel control (esp with big injectors) can be a bit simplistic so not as good as a well light cruise tuned setup

forget all this rubbish about boost and gears and other crap

none of this bears any relevant to light cruise economy

ie; in light cruise the engine is in (or near) vacuum and boost means nothing

driving around in 4th, 5th or 6th shouldnt post much difference

unless you are doing 50km/h in 6th and have to use %100 throttle to maintain road speed

also check the simple things - are you really filling the tank? are you going near empty?

the skylines usually go way past E before they run out and the light comes on

check tyre pressure and other simple things

[paulr33]

and last but not least if you still cant get good economy

give your car with a full tank to a friend or girlfriend or mum

i get they can get over 400km+ to a tank - ie; its probably your driving style

light throttle in low rpm is usually best

constantly loading the engine on boost is bad and will waste fuel (amplified with poor state of tune - ie: a simplistic max power tune)

[Phatboy]

based on what ive seen and read in here i would check 02 feedback is turned on in the hand controller

this is covered in the PFC FAQ (in my signature) check that first, it should be ON by default.

Paul, you are a fu(king genius. I would kiss you if you were a woman.

The O2 feedback control was set to OFF. No bloody wonder I got bad fuel economy.

This should improve my economy. Will post up improvement in results after next tank goes in. Just cannot believe it was something as simple as this.

If my tuner tuned the new turbos and AFRs with the setting on OFF, do I then need to get him to re-tune it now that it is set to ON? Will it lean out the AFR too much?

Thanks so much!

[MrStabby]

Tuning is always done with feedback off, for clarity. You tuner probably just forgot to turn it back on when he finished...You definatly dont need a re-tune.

Good find - it will be interesting to see what you get on the next tank!

[Phatboy]

Tuning is always done with feedback off, for clarity. You tuner probably just forgot to turn it back on when he finished...You definatly dont need a re-tune.

Good find - it will be interesting to see what you get on the next tank!

Cool, thanks. Yeah, can't wait to see what difference it makes.

[Phatboy]

Hmmm quite disappointing.

With 02 sensor feedback turned ON there was no difference in fuel economy.

Still getting 15.6L/100km for mixed city/hwy driving. I drive the same roads on the same days at the same time with the same traffic conditions and driving style all the time, so there is hardly any variation.

The obvious differences that I noticed though, were

O2 sensor feedback OFF

- Smoother idle

- Both 02 sensor voltages 0.00 at idle. Both are responsive and increase similarly when throttling. On cruise, around 0.04 for both.

O2 sensor feedback ON

- Lumpier idle

- O2 sensor 1 voltage around 0.80 at idle, O2 sensor 2 voltage 0.00. When cruising, O2 sensors are around 0.80 and swap around continually

Might need your help deciphering this guys.

Thanks very much.

[joeleo87]

Hmmm,

i got the same problem

my O2 sensor feedback is set to on but the O2 reg is set to off?

what does that do?

also my throttle bodies dont seal 100% due to the fact the teflon coating is no more.

[Phatboy]

How do you know the O2 reg is off??

Hmmm,

i got the same problem

my O2 sensor feedback is set to on but the O2 reg is set to off?

what does that do?

also my throttle bodies dont seal 100% due to the fact the teflon coating is no more.

[paulr33]

im in melbourne, keilor downs

will be easier to come over and we can sort it out

[paulr33]

02 reg is for BNR32

as BNR32 and BCNR33 use same model PFC they need to alter between the different style of 02 sensors

For BNR32

02 feedback on, 02 register on

BCNR33

02 feedback on, 02 register off

if you have BCNR33 and 02 register is on youll get shit economy

if you have BCNR32 and 02 register is off youll get shit economy

make sure you are checking the correct symbol

heres what they look like;

the on / off tells it to speak to the 02 sensors in titania languge vs normal lambda or whatever it is

if you have BNR34 02 register should be off, however im not even sure 02 register is an option in BNR34 PFC

[joeleo87]

so mine should be set to on then paul?

[adis]

I have r33 s2 and this is what Ive been getting per 100KMS.

Just so you guys can compare your own cars. Mods are as per my signature.

11.3L, 11.2L 11.5L 12.6L 11.25L 12.6L 12.4L 10.5L 10.9L 11.3L

Used mainly mobil and bp petrol. Every single test, the driving was mixed, bit of freeway, bit of city and bit of thrashing.

How i measured it:

fill up full tank. 50L, drive and if i get say 450KMS, i would 50L/45km=11.1L

I would love to hear what others are getting?

[Phatboy]

Just had the car serviced today. My mechanic could not detect any intake leaks and the fuel filter was pristine, so he didn't change it.

The mystery continues

Still think it has something to do with my faulty boost sensor...

im in melbourne, keilor downs

will be easier to come over and we can sort it out

Paul, are you talking to me or joeleo87? He lives in Adelaide.

[HEKT1K]

I have r33 s2 and this is what Ive been getting per 100KMS.

Just so you guys can compare your own cars. Mods are as per my signature.

11.3L, 11.2L 11.5L 12.6L 11.25L 12.6L 12.4L 10.5L 10.9L 11.3L

Used mainly mobil and bp petrol. Every single test, the driving was mixed, bit of freeway, bit of city and bit of thrashing.

How i measured it:

fill up full tank. 50L, drive and if i get say 450KMS, i would 50L/45km=11.1L

I would love to hear what others are getting?

i got 17 the other week something is wrong!!

boost gauge i put in recently is reading slightly less vac @ idle than it used to (18inHg vs 20inHg before), but car is boosting and idling fine so i dunno if there's a leak somewhere.

i babied the sh*t out of it last week (NO boosting, rolling down hills in neutral, no driving in traffic) and still returned 14.5L/100km.

ideas anyone? im getting it looked at over the weekend, but it's still worrying me!

[ian]

as per the post above - with the engine rpm increasing it just gets noisier!

Ian

I'm going to do a full post on this, but just a quick comment - mine was definitely the clutch fan. I''ve dropped back to my normal fuel economy since replacing it - in fact with everything I've done to find the problem (air filter, petrol filter, spark plugs, fuel injectors, ecu reset, replace o2 sensor, normal oil and filter change, and probably other things I can't remember. Plus new tires and brakes....) with the final one being the clutch fan - I've got better than ever ie I got 9.8l/100km last weekend when I did a 300km country drive sitting mainly on 100/110km/h..

That is better than when my car was two years old (when I got it) when I got 10.0l/100km on the same 300km trip. Maybe the wind gave me the better .2 this time!

The point is, I was getting 20l/100km around town before, and 16l/100km country. All the other things improved it a bit, but the final bigy was the clutch fan - so do check it! A brand new one cost me less than $200..

Ian