Really bad MPG (Legacy Turbo 93)

[Mpgingerson]

For some while now my car has bad MPG, and it's noticably bad from before. Any things I should look at? What about a worn fuel filter?

And this started happening after I installed an Apexi intake and filter with coffee cup in it.. I plugged a nipple on the charcoal canister, does this maybe have anything to do with it?

[turbo970]

depending where you live it could be the winter mix fuel.

[Mpgingerson]

depending where you live it could be the winter mix fuel.

I live in Norway, so maybe yes.

[Legacy777]

I suspect the issue is probably related to the intake. On the stock setup the MAF sensor pulls air in to minimize turbulence. With the pod style air filter and intakes that creates a lot of turbulent air which can affect the MAF sensor reading, which will have a direct impact on fuel economy and power.

Do you have a wide band O2 sensor? If so, how have your AFR's looked before and after putting the intake on?

Have you tried putting the stock intake setup back on to see if your mileage, power, throttle response changes?

It's always a good idea to reset the ECU after performing modifications or reverting to stock so the ECU learns appropriately.

[Mpgingerson]

I suspect the issue is probably related to the intake. On the stock setup the MAF sensor pulls air in to minimize turbulence. With the pod style air filter and intakes that creates a lot of turbulent air which can affect the MAF sensor reading, which will have a direct impact on fuel economy and power.

Do you have a wide band O2 sensor? If so, how have your AFR's looked before and after putting the intake on?

Have you tried putting the stock intake setup back on to see if your mileage, power, throttle response changes?

It's always a good idea to reset the ECU after performing modifications or reverting to stock so the ECU learns appropriately.

Yeah I thought it would be the intake and no I sadly don't have an O2 sensor, so I don't know how rich or how lean it's running, but when I bought the intake it was originaly to make space for tubing to the FMIC, but I haven't bought one yet and I fell into the temptation to install the intake with to remap or anything, just an ECU reset.

But yes, I will remove this evening and clean the MAF sensor, and do a reset.. I'll see if it helps! but what are the symptoms of a bad fuel filter? (Bad idle, or?)

[Legacy777]

Be careful with cleaning the MAF sensor as they can easily be damaged. Make sure to use MAF sensor cleaner.


Regarding the fuel filter, a "bad" fuel filter can be many things, collapsed, plugged, dirty, etc. However, I would say the most similar resultant cause will be fuel starvation, especially under heavy engine load (higher boost). If you don't have bucking or running lean issues under boost the fuel filter probably isn't the first place I'd start looking. However, if you don't know the last time it was replaced it wouldn't be a bad item to replace from a maintenance stand point so you know it's good.

[Mpgingerson]

Be careful with cleaning the MAF sensor as they can easily be damaged. Make sure to use MAF sensor cleaner.


Regarding the fuel filter, a "bad" fuel filter can be many things, collapsed, plugged, dirty, etc. However, I would say the most similar resultant cause will be fuel starvation, especially under heavy engine load (higher boost). If you don't have bucking or running lean issues under boost the fuel filter probably isn't the first place I'd start looking. However, if you don't know the last time it was replaced it wouldn't be a bad item to replace from a maintenance stand point so you know it's good.

Tried swapping to the original setup again, it didn't work Maybe a bad MAF or bad O2 sensor? How about the fuel pump, injectors? Anything to look at?

[Mpgingerson]

My car uses 28 MPG? Not sure if that's right.. I measure in Liters per km/mile, not gallon per miles.. It was around 1 Liter per mile (per 10 KM ).. This is with no driving above 3000 rpm and casual usage of the gas pedal, and an average speed of 40-45 mph..

Mods are: Just a backbox, stage 1 clutch, LW flywheel and the APEXI intake. But maybe I should mention that sometimes the car fuel cuts, just sometimes and it has been doing it ever since I put on the intake, I'll install a boost gauge maybe tomorrow to see the boost levels, but it's weird that it overboosts, no?

[mike-tracy]

Are you sure it uses 1L per mile? What were you measuring in L/100km?

if I got my math right,
1L/1Mile is just under 3.785 mpg or 60.7L/100km
I truly hope that's a mistake.

[Mpgingerson]

Are you sure it uses 1L per mile? What were you measuring in L/100km?

if I got my math right,
1L/1Mile is just under 3.785 mpg or 60.7L/100km
I truly hope that's a mistake.

I'm not sure if it's right, because I used a conversion through Google.. But i'm not sure if a mile in Norway is the same as English miles. I filled the car full, and drove casual with a tripmeter going and double checking the distance I had traveled, and it came to around 7,25 L when I drove 72-75 Km's.

[mike-tracy]

OK, so 7.25L/75km works out to 9.7L/100km which is 24.33 mpg. That's on the good side of normal for these old cars. I am using American gallons, as English gallons are a different size and would throw another confusing variable into the mix. I am pretty sure the mile is the same on land though.

Is this better or worse than when you started this thread?

[Mpgingerson]

OK, so 7.25L/75km works out to 9.7L/100km which is 24.33 mpg. That's on the good side of normal for these old cars. I am using American gallons, as English gallons are a different size and would throw another confusing variable into the mix. I am pretty sure the mile is the same on land though.

Is this better or worse than when you started this thread?

Oh okay... Maybe I'm getting to cheap on the gas money and I've started to notice every inch the gas gauge creeps But changing the setup to stock didn't change anything, still the same.. But I'll change back to the Apexi then, since the throttle response was much sharper and I miss the loud intake noise it made haha..

But is there any way to improve MPG? I'm guessing you can always improve MPG by changing certain worn parts and such?

[Mpgingerson]

How about a new fuel pump? A Walbro 255?

[Legacy777]

A fuel pump is not going to change mileage.

An O2 sensor may help. If the MAF sensor is bad that will also affect mileage. If the injectors are not flowing optimally that could affect mileage as well.