Hey all. Need opinions. My 09 f-150 with the 4.6 3v has had a considerable drop in fuel economy. Was getting 22 highway and 16 in town and about 13 towing on average 4k pounds. After I hit 50k it started to drop and now at 70k I'm getting around 7-8 towing, 12 in town empty and 16 highway... Any others seen anything like this?

 

Have you also lost power? If so, or, either way, you might have clogged catalytic converters. It can really sneak up on you, slowly increasing backpressure so you don't notice it, in the process sapping mileage and power. Check it out!

 

No power is still the same. Really impressed with it being a 4.6, especially coming from a few diesels. I'll check out the cat. Is there a way now to clean em, or is it replacement...

Thanks

 

You may need to replace the air intake filter. Take a look at it anyhow. Also, if you have changed fuel supply or octane rating you may need to use the 87 octane fuel. It's difficult to diagnose a truck online. It's a good idea to let the dealer troubleshoot it.

 

Do the '09s have lifetime fuel filters in them? If not, it may be worth changing it. Just a thought.

 

Yeh I've thought Bout the fuel, but was told by someone at ford it's not a good idea to change until 100k... Made no sense to me...

Air intake filter? Never heard it called that unless this is different from the air filter...that's been replaced twice... And looks fine. Always used the same fuel. Always been 87 from either shell or Valero.

Dealers around here are crooks. Wanted to get some opinions here first since I've had good help in the past.

 

The fuel filter is in-tank and supposedly "lifetime".

 

It's difficult to imagine a 6 mile per gallon fuel consumption difference with an engine that seems to be running normally. I would be parked at the service department until the issue is identified and corrected.<O</O

 

As far as fuel filters are concerned, if it were clogged it would run worse, or not at all, but all that time consumption would NOT go up, as the engine would be starving for fuel, rather than getting too much. The only filter that would increase consumption by clogging would be the air filter, and that has been dismissed as the culprit here.
The mystery continues.......

 

Maybe you should take it in and have the mapping checked? An immediate drop like that would make me think ignition (i.e. plugs, timing) or a mapping issue.. If nothing has really changed I would start there.

 

Another consideration may be the spark plugs. Although the spark plugs and other tune-up components are generally good for around 100,000 miles, with 70k miles on a truck you could have a single or more than one plug that may not be performing as it should. This would definitely affect the fuel economy.<O</O

 

well a clogged fuel filter can affect fuel mileage. Like stated above, its hard to internet diagnose. So this truck has all fresh fluids and filters, plenty of power, and you have noticed no change except for gas mileage?

 

But only by DECREASING it. The problem here is a sharp INCREASE in consumption. A restriction in fuel flow does not increase consumption. I've had loaded fuel filters before, so loaded the engine would hardly run, but fuel consumption did NOT increase.

 

A failed or failing oxygen sensor can cause poor fuel eco and loss of power. A scan for codes often can reveal if this is the case. There are often more than one O2 sensor in most vehicles/trucks. I'd suggest a scan for codes regardless as that could possibly tell you about the O2 sensors, MAP sensor and other issues that may be causing this.

 

While I agree that failure of any sensor would put the engine in "limp home" mode, I wonder if it would cause as great a drop in mileage as is reported here. I didn't think so, but I really don't know for sure. Maybe multiple-sensor failure, but would it even run then? And it's STILL a mystery....