Fuel economy issue

[LegacyB4]

Another random question...this time about fuel economy.

Now that my B4 is approaching the 200k mark, there are a number of issues that is popping up. Most of it is just general wear and tear and due to recent financial restraints, I havent been able to get on top of it. So its fair to say that things are starting to mount up

However....I have noticed over the last month my fuel economy has decreased drastically. I normally would get around about 450kms from a full tank of gas, now I get around 300 - 350kms.

What would cause a drastic drop in fuel economy? I love my car but this is seriously starting to get on my nerves!! Any advice or ideas to point me in the right direction would be greatly appreciated

[reaperblitz]

Do a full service. Oils plugs and oil and air filters.

See how that goes. Also inflate tires and don\'t use your car as storage.

Lol

[sirwrx]

What sort of driving are you mainly doing?

When I had my BH GTB i would get around the 450km per tank driving between Westport and Christchurch with some running around town. Lots of hills and corners to slow you down.

I then drove down the Canterbury plains and back and got closer to 600km per tank.

If I was at home in Westport I would get somewhere around 350-400km per tank as it was very short running so the motor rarely got to operating temperture.

So you can see that the type of driving can have a drastic effect on fuel economy.

If the type of driving hasn\'t changed then as above, do a good service and see if that improves the fuel economy

[Firenza]

Any other tips to look at? I have a BF GT and am only getting 300kms out of it with town driving, whereas my wrx gets over 350-400 with the same use.

Car is fully serviced, new plugs, new oils. Cleaned the airflow meter.

[LegacyB4]

Would an 02 sensor be a contributing factor? That issue seemed to come up alot on the UK legacy forum. My car is duue for a service, but its only 1000kms over due....Im sure that wouldnt be the sole reason drinking too much juice

[Kiwiflyboy]

When I brought mine almost 3 years ago i Used almost a whole tank to get from Christchurch to Tekapo. When i got back we had a look and found out both the knock sensor and Oxygen sensor were buggered so was pouring in way more gas than needed. Once they were placed and ECU reset car used way less!

[tebbyj]

 LegacyB4 said:

Would an 02 sensor be a contributing factor? That issue seemed to come up alot on the UK legacy forum. My car is duue for a service, but its only 1000kms over due....Im sure that wouldnt be the sole reason drinking too much juice

Get the 02 sensor tested as they do wear out Bosch recommend replacing them at regular intervals. They get lazy and can cause the car to over fuel.

And you\'ll be surprised how much difference a good (full) service with the correct materials makes.

[MoJoe-95Legacy]

try checking your injectors. my fuel economy shoot down alot cause one of my injectors crapped out.

[MoJoe-95Legacy]

 tebbyj']

[quote name='LegacyB4 said:

Would an 02 sensor be a contributing factor? That issue seemed to come up alot on the UK legacy forum. My car is duue for a service, but its only 1000kms over due....Im sure that wouldnt be the sole reason drinking too much juice

/quote]

Get the 02 sensor tested as they do wear out Bosch recommend replacing them at regular intervals. They get lazy and can cause the car to over fuel.

And you\'ll be surprised how much difference a good (full) service with the correct materials makes.

you can tell when a 02 sensor has crapped out when your car starts running rich or lean. I THINK ??? :-\ ??? 8)

[tebbyj]

 MoJoe-95Legacy']

[quote name='LegacyB4 said:

Would an 02 sensor be a contributing factor? That issue seemed to come up alot on the UK legacy forum. My car is duue for a service, but its only 1000kms over due....Im sure that wouldnt be the sole reason drinking too much juice

/quote]

Get the 02 sensor tested as they do wear out Bosch recommend replacing them at regular intervals. They get lazy and can cause the car to over fuel.

And you\'ll be surprised how much difference a good (full) service with the correct materials makes.

you can tell when a 02 sensor has crapped out when your car starts running rich or lean. I THINK ??? :-\ ??? 8)

;D yes and no, car will definitely alter mixtures if O2 Sensor is bung but sometimes the sensor doesn\'t actually stop working. It just gets stuck (per say) so computer thinks its fine and runs that mixture which might not suit the operating condition.... if that made sense.

Ie: O2 sensor gets stuck at .7v and the car thinks thats rich so it leans the mixture, which would cause rough running when cold, and under heavy acceleration.

[familyman]

 Firenza said:

Any other tips to look at? I have a BF GT and am only getting 300kms out of it with town driving, whereas my wrx gets over 350-400 with the same use.

Car is fully serviced, new plugs, new oils. Cleaned the airflow meter.

Hey man, I had dreadful fuel economy in my BC5 when I first bought it. Was 2 full tanks from Auckland to Blenheim.

I found that by replacing the very crappy aftermarket sponge unifilter with a genuine panel filter in factory airbox, the fuel economy improved quite a bit.

I also fitted a V2 STI ECU and found that it improved even more, even though it has a "more aggressive" map. I can only assume that the change from 8 bit ECU to 16 bit ECU helps the issue as well as a further 5 years of tuning from factory.

[jost]

 Firenza said:

Any other tips to look at? I have a BF GT and am only getting 300kms out of it with town driving, whereas my wrx gets over 350-400 with the same use.

Car is fully serviced, new plugs, new oils. Cleaned the airflow meter.

Smaller, lighter and later model car, It\'s suprising the differences a few years make with fine tuning and better economy

[nickmcgill]

Speaking of knock sensors does any one have a tool to test them ?

When I hook the ECU up through FreeSSM it always reads the knock sensor as 0.

Not sure if it\'s faulty or not reading it properly.

[Firenza]

 familyman']

[quote name='Firenza said:

Any other tips to look at? I have a BF GT and am only getting 300kms out of it with town driving, whereas my wrx gets over 350-400 with the same use.

Car is fully serviced, new plugs, new oils. Cleaned the airflow meter.

/quote]

Hey man, I had dreadful fuel economy in my BC5 when I first bought it. Was 2 full tanks from Auckland to Blenheim.

I found that by replacing the very crappy aftermarket sponge unifilter with a genuine panel filter in factory airbox, the fuel economy improved quite a bit.

I also fitted a V2 STI ECU and found that it improved even more, even though it has a "more aggressive" map. I can only assume that the change from 8 bit ECU to 16 bit ECU helps the issue as well as a further 5 years of tuning from factory.

When I first bought it I did a hard core service on it, and that included replacing the nearly new but not OEM air filter for a Subaru one

Anywho, i have noticed that the knck sensor is in the wrong place on the intercooler mount so gonna try moving that back, and im going to replace the up pipe as I think that could be causing the issues.

And re. it being a older heavier car, from talking to other people it should be capable of better, and as it sounds like shit at the mo, im thinking to two are related

[Kiwi_Fozze]

 nickmcgill said:

Speaking of knock sensors does any one have a tool to test them ?

When I hook the ECU up through FreeSSM it always reads the knock sensor as 0.

Not sure if it\'s faulty or not reading it properly.

iirc the knock sensors are a basic yes no sensor, if it detects knock then for the instant it detects it, it\'ll read 1 or 16 or something, rest of the time it\'s not so will be producing the 0 reading.

bit like the neutral position sensor, reads 1 in gear, 0 out of gear

[nickmcgill]

Ah thank you good sir that clears that up

[jost]

I just put a BG non turbo back on the road, was an EJ20, dropped an EJ25 in the hole running EJ20 Manifold and ecu but economy sucked, had new air filter, plugs, oil and filter change, but still using about 15L per 100km, Ran a can of Three Bond engine conditioner ($15 Partmaster) through it and huge difference, Smoother, quieter, and now down to 9L per 100km.

Tail pipe is now nice and clean, running car on 95.

[Divine]

 jost said:

I just put a BG non turbo back on the road, was an EJ20, dropped an EJ25 in the hole running EJ20 Manifold and ecu but economy sucked, had new air filter, plugs, oil and filter change, but still using about 15L per 100km, Ran a can of Three Bond engine conditioner ($15 Partmaster) through it and huge difference, Smoother, quieter, and now down to 9L per 100km.

Tail pipe is now nice and clean, running car on 95.

That wouldn\'t suprise me running an EJ25 with an EJ20 ECU

[jost]

 Divine']

[quote name='jost said:

I just put a BG non turbo back on the road, was an EJ20, dropped an EJ25 in the hole running EJ20 Manifold and ecu but economy sucked, had new air filter, plugs, oil and filter change, but still using about 15L per 100km, Ran a can of Three Bond engine conditioner ($15 Partmaster) through it and huge difference, Smoother, quieter, and now down to 9L per 100km.

Tail pipe is now nice and clean, running car on 95.

/quote]

That wouldn\'t suprise me running an EJ25 with an EJ20 ECU

Actually both cars run red injectors, green AFM and same ECU. (was a suprise to me too) Just uses the O2 sensor to control fuel delivery

[LegacyB4]

Is it normal to have a 15L/100km for a turbo B4?

[jost]

 LegacyB4 said:

Is it normal to have a 15L/100km for a turbo B4?

Should be around 10L/12L depending on how you drive it, and of course will use more the harder you push it, i once got one up to 25L/100KM

for poor economy start with the basics, plugs, oil and filter, air filter, then check for any errors that could have a negative effect on economy, Try some three bond engine conditioner, it\'s cheap and worth trying.

O2 sensors, Knock sensors and coolant temp sensors (the one under the manifold with 2 wires) can also have negative effects on economy if worn.

And also check for vacuum leaks, That\'ll kill your ecomony.

[Marky]

Foot heaviness and the duration of trips has a huge impact too (when it\'s in cold start fuelling it chucks the gas down)

Mine had a month of mainly very short trips and/or me driving it - got about 300km to a full tank - the latest tank which is wife commuting to work 90% of the time it has ticked over 520km and light isn\'t on yet, also managed a touch over 600km on an open road trip

The EJ25/20 sensors thing makes sense too - nissans do a few things similar also