Strick9

I've got 128k miles on my 06 GT. I've noticed in the last 6 months I've been getting about 100 miles less per tank of gas. I've tried everything: fuel filter, tire pressure, air filter, fluids, slow driving, etc. I get no irregular idle rpm, no smoke, no anomalies. Anyone having these issues? Any suggestions? I even tried fuel additives and high octane fuel with no changes. Thanks for your input.

SplitSecond

At 10 years and 128k I would replace your O2 sensors. Those are a part of major tune ups that most people forget about. Your O2 will tell the PCM if it needs to add/take away fuel from the mixture so they can be messing with a proper A/F ratio and dumping more fuel into the cylinders.

Bad O2s can throw SESs but I've seen old ones do some crazy stuff without a light coming on.

Imatk

What he said

Cavero

O2 seems pretty likely. Get some MAF cleaner on the mass air sensor too. Especially if you have a K&N filter (or other oiled filter). The oil can get sucked down the intake and coats the MAF sensor. Check to see if the throttle body needs a clean too.

Cavero

oh yeah, when was the last time you changed your spark plugs?

GottaHaveIt

I pulled my fuel pump cleaned the pickup /sock/ strainer & gained 100 kilometres a tank , so every 3 months I repeat it , also having an oil seperater to keep the throttle body & mad sensor cleaner help.😋

Strick9

I installed new spark plugs at 100k and new fuel filter at 120k. I've never changed O2 sensors or cleaned the MAF. I do have a BBK 62mm throttle body and k&n filter. Are O2 sensors something I can do at home? I've never messed with them. Also no check engine light either.

SplitSecond

If you can do them at home depends on the location of them. I am not familiar with where they are on 4.6s but it should be fairly easy to find a diagram on google.

O2s will be bastards to get out after 128k especially if your car sees rain/snow. The easiest way I have found to get them out is using a torch to heat it and a breaker bar if you can fit it in there. They sell special O2 sockets that fit over the wires, but if I'm replacing them I just cut the wires off the sensor and put a regular socket over it.

Soaking the threads in PB Blaster a few days ahead of time will help but be careful if you are using a torch, PB Blaster is flamable.

Imatk

I wouldn't attempt it... and I've installed exhausts, supercharger, heat exchanger, etc.

I'd want a lift before I'd try that.

Strick9

Ok I bought some MAF cleaner and found some how to videos. I think I will leave the O2 sensors to the pros. Hopefully I will see an improvement after the MAF cleaning.

Strick9

What's the advantages to having an oil separator?

Noilly Pratt

I've nursed cars up to high mileages, and I'd agree with the O2 sensor diagnosis.

Also, check any vacuum hoses - at that age they should be OK but if anyone is reading with higher mileage, a vacuum leak can cause all sorts of strange things to happen, sensors misreading etc.

07 Boss

How does changing cleaning out your pump filter get you better mileage? That's silly to state something like that.

And OP, do you actually check your mileage? My mileage can vary from 110 to 210 miles per tank depending on what kind of driving, avg speed, traffic conditions, etc.

Strick9

I used to consistently get between 300-350 miles per tank. Now I'm lucky if I get 250. Driving style hasn't changed.

07 Boss

Do you track mileage against what you actually pump into the tank each time? Maybe it's a tank fill problem or a bad tank crossover. Reset mileage when you fill up. Next time you fill up divide that mileage by the gallons you pump in. Then multiply that by your tank capacity. What does your computer say your miles per gallon average is?

unnoticedtrails

I wish I could get 350. The most I have ever gotten out of my current '06 V6 auto is 295. My grey car I had with the same drivetrain, but a year newer (more miles) I could get 310 if I was lucky and lots of highway. The only differences between the cars is the grey one had an SCT X3 Tuner and Steeda CAI.

Sorry to interupt the conversation on V8 mileage.

Strick9

I always reset and I always wait till the tank is practically dry ~50 miles left. That's another problem. The computer says I'm getting 24-27mpg on the freeway which should translate to 300-350miles/tank but it's not.

07 Boss

You're being evasive with the numbers we need. How many gallons are you putting in when you fill up? How many miles are you driving before filling up? I just think you're not calculating things properly. When you say you fill up with 50 miles to empty that can be anywhere from 9 to 12 gallons to fill it up. You have at least 2 if not 3 gallons left in your tank. Look where my car says 50 miles to empty.



That is just above 3/8 of a tank which means I have just a little more than 5 gallons in there. If I fill up at this point I only get 10 gallons into the tank.

Don't reset your mpg computer for at least 3 tanks and then tell us what it is. This will give you a more accurate figure. Getting 24-28 on the freeway doesn't tell you anything. I can get my mileage computer to say anywhere from 2.3 mpg to 99.9 mpg at any given time. Tell us exactly how many gallons you are putting in and how many miles you have driven. And don't reset your average speed number either. Run that along with your MPG computer and give us those numbers.

The couple of figures you gave us are pretty vague. I mean if your getting 100 miles less per tanks than the 350 you say you were getting before means that you are getting 250 miles per per fill up. And if your filling up with 50 miles to go that means you are getting 18.75-19.25 mpg which is decent, not great but not bad.

I'm sorry I thought our fuel tank capacity was 14 gallons but it is 16 gallons so I will edit the above to reflect those numbers.

Strick9

I'm not trying to be evasive. Every tank I have filled up between 13-15 gallons since October and I'm getting max of 250 miles. Now let's say for instance I fill up 13 gallons and I get 250 miles until I fill up and it takes 14 gallons to fill then next time. So I used 14 gal for roughly 18mpg. Now my computer uses an instant average which has huge fluctuations I know that. But to go from 350 miles to 250 miles using the odometer for a single tank is a huge difference. I'm talking a 7mpg difference. That's the problem.

Bert

Miles per fill-up is a meaningless number. Use miles per gallon and then things might start to make more sense.

The first thing to do is make sure all of the normal recommended maintenance has been done, before you start chasing other wild geese. That's why things like the fuel filter should be done, even if it is not obvious how that would contribute to a fuel efficiency issue.