Shocking Fuel Economy. What Sensors To Replace

[Moodles2]

When injectors get clogged/dirty they lose their factory spray (mist) and turn into a leaky tap, could explain why it's running rich.. no way to know for absolute sure unless the injectors are taken out and cleaned&flow tested.

There has to be a reason why there is excess fuel being dumped in, someone has suggested looking for a Atmo BOV which would cause the car to stall while slowing down and running rich (metered air being dumped to the atmosphere before it reached the engine instead of being re-circulated as the stock ecu expects).. although you would know you have one by the wanky noise.

[reeceo21]

Stock Bov mate. had a talk with the old owner who had her for 7 yrs. He reckons that it would be the AFM because it went faulty on him once and caused shit fuel economy but said it was doing its thing fine. But i suppose the injectors would be due for a clean, or would it be worth getting newys. Thanks mate for the suggestion wouldnt have bothered getting injectors done if it wasnt for your input. Ill get quotes tommorow

[89CAL]

No MAP sensor on RB20's. Well not that interact with the ECU anyway

I'd try and borrow an AFM to try that.

Silly question but could it be your driving style?

[reeceo21]

Yes cal my driving style will contribute. BUT my mechanic has had all his scan tools on there and the car runs very rich that is the problem. i had to fill up to the brim twice coming back from Melbourne so a 500k trip this was full to empty each time.

[89CAL]

What AFR's was it running at cruise speed?

[reeceo21]

Do you mean the how many volts the afm was uaing, well idle it was 1.5 and when giving the beans it was 5 volts

[89CAL]

No I mean AFR.

AFM Voltage is irrelevant for me because it doesn't determine how much fuel the engine is getting at a certain point. It merely tells how much air is coming in to the engine so the ecu can work it out

If your hitting 5v at WOT then sounds like your maxing out the AFM anyway

[reeceo21]

Ok.mate so possible faulty afm

[89CAL]

Not necessarily. You can max out your AFM with higher airflow then it was designed to meter but if you only have a standard RB25 turbo bolted on it shouldn't max your AFM

[reeceo21]

Ok dude so what would you reckon would be the best bet

[GD2ILA]

to op, my story:

for the last 1 to 1.5 years i've been getting around 280 to 320km a full tank (60 liters) so thats's 18.75 liters/100km, i've just changed my fuel filter and now i'm getting 390-440km a tank (so i've wasted so much fuel this last year because of a dirty $20 fuel filter). Just from changing my fuel filter my economy is from 18.75 liters/100km to now 13.63 liters/100km. so if you haven't try changing your fuel filter and see how that goes. good luck.

[blind_elk]

fuel pressure was fine he tested it. he would clamp the hose and the pressure would go really high indicating a good pump.

Then he had a gauge connected. What did it read? Just because it has "good" fuel pressure doesn't mean it has "correct" fuel pressure.

he said not to bother as they were working when it comes to injectors. they were working fine apparently and the problem is running rich

If the injectors are dirty, they can hold the needle slightly open, allowing too much fuel to enter the engine. Result = RICH. So, are the injectors clean and flowing correctly?

[89CAL]

I said it my first post, put it on a dyno and check AFR's, AFM voltages wont tell you the full story. For the reasons that have been listed in the post above plus many more, everything could be alright on paper, but your car is running Rich and causing bad fuel economy. Take it to a tuner and ask him to put it on the dyno and check the AFR's

Sensor voltages are really just inputs to the ECU, 4V at the AFM doesnt mean its going to put X amount of fuel into the engine.

[ms33]

I've recently just replaced one of my O2 sensors, and my fuel economy has increased by a huge amount. So will be checking them on a regular basis.

I read online that having a faulty O2 sensor, you can use up to 30% more fuel.

[Got a Pulsar]

Yep, I recently replaced my O2 sensor with a cheapish one from Vulture Motorsport.

http://www.skylinesa..._gopid__6063325

Also reset the ECU. Economy went from 300 km / 45L = 15L / 100km to 400km / 47L = 11.75L / 100km.

Definately worth trying this. Cheerin'.

After a few weeks I cleaned the AFM, which didn't seem to change economy but it did stop an issue at 10psi boostin' time.

Edited October 15, 2011 by Not a Pulsar

[mad082]

I've recently just replaced one of my O2 sensors, and my fuel economy has increased by a huge amount. So will be checking them on a regular basis.

I read online that having a faulty O2 sensor, you can use up to 30% more fuel.

yeah at light load the o2 sensors make the car run at around 14.5:1 AFR, if you unplug the o2 sensor, at the same throttle load it will run richer at aroung 12:1 AFR

[reeceo21]

I have recently lost my job so fuel economy isnt a problem because im on the bike at the moment. but from the sounds of it my goal is new o2 sensor and then get it on the dyno. i have done the fuel filter recently and no avail. Oh and most importantly injectors checked out

[040122]

at least you didnt just buy $640 woth of splitfires n see almost no difference

[89CAL]

Coilpacks wouldn't make to much difference on fuel economy (unless they were colpletely wrecked)

Most of your fuel economy comes from your lean cruise cells which don't require a strong spark. The coilpack issues mainly occur under boost/load when the spark needs to be strong

Having said that splitfires are good for later on when you decide to start modding more

[boiracer]

lots of talk of the AFM being faulty or having the right voltage but have you cleaned the AFM??? i dont think ive seen this mentioned yet...if so, sry i missed that. if your running an oil charged pod filter, they like to make AFM's dirty.

check for an air leak?? maybe in or near the TPS ( random idles are often this)

good luck...i couldnt imagine this sort of economy. the all wheel drive i guess would make it a bit more than a 2WD, but not that much...ouch. i get 400-500 out of my 33 GTST tank. 400 is with happy driving and happy laps. 500 is on the highway with my economy sponge installed (i have seen 600km out of a tank)