vr v6 bad fuel economy

[brend94vr]

ok guys, i have recently had a sports catback exhaust put on 2 1/2 inch, and ever since then my fuel economy has gone to crap, i drive very light footed and dont thrash it, but im getting around 180kms out of a full tank where as with the stocky i got 350, i have tried switching fuels i have tried the e10, 95, and 98, and only a few kms difference is this normal???

[GothicKidd]

Might have to put it back on? O.o until you can get extractors? Im guessing your a P plater so no extractors for you..:\
My car gets 400ODD k's from a full tank with only a lukey 2 1/2" catback.. :\

[brend94vr]

nah full licence, i had the exhaust done cause i was in an accident

[Krilnik]

I too wanted to throw on a more free flowing exhaust to improve my fuel economy.

But after speaking to a few exhaust places, they have advised me that a free flowing exhaust will improve highway fuel economy and will NOT benefit an attempt to achieve better fuel economy around town/city driving. 90% of my driving is city traffic so i chose to leave the stock exhaust on as per their recommendation.

What type of driving are you doing? Mainly highway? Slow stop start city traffic???

[brend94vr]

slow stop start traffic

[Krilnik]

Well there you go.

Do what i did, speak to a few exhaust places and get their opinions. ALL of them told me the same thing:

Free flowing exhaust - improved highway economy / reduced town, city economy


In other words, it would reduce my economy. Once again, every exhaust place i went to told me this.

[brend94vr]

guess the only thing i can do is get a long range fuel tank then

[James39]

Still should be getting more than 180k though.. My stock VR would get around 400...

[monkeys437]

Your probably putting the foot down more when accelerating to make up for the power loss from the bigger exhaust. That wouldn't be helping the economy either

[brend94vr]

i dont put the foot down at all

[Krilnik]

guess the only thing i can do is get a long range fuel tank then

You'll still use the same amount of fuel.

Is it really worth having the aftermarket exhaust on? Is it really providing that much more power?

I personally choose fuel economy over power.

I'd rather save money and fill up less often then have slightly more power to drag off a bus.

[brend94vr]

well if i take it off i have wasted the $380 putting it on

[Wombles]

But if you leave it on your doubling the amount of fuel you use.
More fuel, less k's, more times to fill up = waste of money in the long run.

[hako]

Check they didn't move the oxygen sensor location - if they did the engine will run in open loop or closed loop (I always get them mixed up) which will mean you use much more fuel. Also check you coolant temp sensor which tells the ECU when the engine has reached operating temperature....if it's buggered it will think the engine is cold and feed more fuel in.

[brend94vr]

i think the oxygen sensor is the problem have had the check engine light come on and go after i stopped

[hako]

i think the oxygen sensor is the problem have had the check engine light come on and go after i stopped

That will be the reason for the extra fuel used. Get it fixed soon as the excess fuel will damage the catalytic converter. New sensors are on Ebay pretty cheap...VR has 1 from memory.

[brend94vr]

yea only has one, will get it done with the service

[PRAVX II S]

Check for codes bridge pins 5&6 on the diagnostic connector.
You can check if the 02 sensor is working or not With a multi meter.
The best way is to check the 02 would be on a graph.

Owe and for hako its open loop when the o2 does not work.

[hako]

Owe and for hako its open loop when the o2 does not work.

Just got to remember which is which!....so in open loop the ECU uses a default figure?

[stuntmanmike]

A 2-1/2" system is a little too big for a stockie V6. A 2-1/4" is better for street duties. Anyway...
The "faulty O2 sensor" code might not show up using the diagnostic mode.
My V6 has a 2-1/4" free flowing system and on closed throttle the "engine alert light" used to illuminate. Blipping the throttle would turn off the "engine alert" light.
I reckon your fuel consumption has gone to the dogs coz your O2 sensor is not feeding the inputs to the ECM the way it should.
FYI having silicon go through the engine will stuff a O2 sensor in no time.
Maybe try a new O2 sensor firstly like the others are suggesting. If that does not work or change your fuel consumption then maybe consider selling the 2-1/2" set up and use the funds to offset the purchase of a 2-1/4" system. The 2-1/2" system will work well with a stockie 5 litre.
Best of luck...

[hako]

maybe consider selling the 2-1/2" set up and use the funds to offset the purchase of a 2-1/4" system...

A couple of hits with a hammer to flatten the pipe a bit works the same!

[petergl67]

Pipes way to big exhaust centre should of known better. Maybe change ur sensor and see if that helps. Better doing that than changing the hole system back and see what happens. But thats shocking fuel consumption. Even though it's stock maybe memcal.

[PRAVX II S]

Just got to remember which is which!....so in open loop the ECU uses a default figure?

Well think of a electrical circuit with a light globe when its OPEN circuit the light will not work (open loop condition)
Now the circuit is closed the light globe glows (closed loop condition)

Open loop will still use other sensors other then the o2 sensor, Like ECT,TP,MAP,RPM to deliver the right amount of fuel.
When the o2 is at operating temp and see's cross counts its in closed loop and can fine tune the fuel delivery via feedback.

[hako]

Well think of a electrical circuit with a light globe when its OPEN circuit the light will not work (open loop condition)
Now the circuit is closed the light globe glows (closed loop condition)

Open loop will still use other sensors other then the o2 sensor, Like ECT,TP,MAP,RPM to deliver the right amount of fuel.
When the o2 is at operating temp and see's cross counts its in closed loop and can fine tune the fuel delivery via feedback.

Thanks - the open/closed bit makes sense. I'll read up on O2 sensors....didn't realise they could make as great a difference in fuel consumption as the OP is experiencing.

[PRAVX II S]

Thanks - the open/closed bit makes sense. I'll read up on O2 sensors....didn't realise they could make as great a difference in fuel consumption as the OP is experiencing.

Well we are not sure if the o2 sensor is at fault. Remember its a o2 sensor it sences how much o2 is left.
you would need to put it on a graph and see the cross counts and how far apart they are also the voltage coming out of it.
If the o2 is stuck on lean the ecu will make the injector pulse wider. hence the fuel issue.