Poor Mileage, all of a sudden, worse than normal!

yosemitesamiam · #1 (**permalink**) 06-14-2009, 07:27 PM

Hey all...I know it has all been heard before. Also posting this in Exped forum. Just some background here:

1999 Expedition XLT, 4x4 5.4. 3.73 rear axle, etc etc. I know, I'm already set up for failure here....however that said, I was pretty used to seeing 13.5-14 town, and 16.5-17 highway. Now, no matter where we go, we get 10.3. City/highway, doesn't matter....10.3.

I'm not getting codes, I'm not running rough. I am noticing heavier than normal black stuff accumulating at the tailpipe...of course because it is running rich.

My first instinct was to check the Coolant Temp Sensor....it is the only thing I can think of that besides stuck open or shorted, will not throw a code, but will make the engine run as if it were cold all the time. Then I discovered that I don't have a Coolant Temp Sensor...that seems to be Navigator only this year this engine.

Anyway, any other guesses, other than someone siphoning the tank, or a flat out fuel leak that I can check for? Again, running great...just sucking way more than normal fuel.

Thanks guys.

Sam

Fishin76 · #2 (**permalink**) 06-15-2009, 08:44 AM

Air temperature Sensor will do the same thing.

torkum · #3 (**permalink**) 06-15-2009, 09:13 AM

Try cleaning your MAF with a approved cleaner. A little dirt on the wires could cause a false reading.

yosemitesamiam · #4 (**permalink**) 06-15-2009, 09:48 AM

Yeah, tried the MAF. Its been hosed with MAF cleaner. LOL. I have not looked at the Air Temp Sensor however...any ways to check it via volt meter, etc?

Also in regards to oil consumption. Now using about a quart every 1,000-1,200 miles or so. Checked the easiest thing, PCV...it is fine darn it. Have lots of pooled oil down in the gully below the intake.

wb6anp · #5 (**permalink**) 06-15-2009, 10:51 AM

Check the torque of your rocker cover bolts, loose bolt could account for the pooled oil.

Fishin76 · #6 (**permalink**) 06-15-2009, 08:33 PM

Yeah, there is a way to test, but I don't know what it is. The air temp sensor is cheap enough, I say just replace it. Thats what I would do. As I grow older, I'm finding that time is more expensive than parts, (most of the time), And I have less and less of it to spend diagnosing cars.

JJ98 · #7 (**permalink**) 06-24-2009, 02:20 AM

what the miles on the vehical at might be time for 02 sensers or the or the plugs could be bad by miles to many little what if

yosemitesamiam · #8 (**permalink**) 06-24-2009, 02:26 AM

Quote:

Originally Posted by JJ98

what the miles on the vehical at might be time for 02 sensers or the or the plugs could be bad by miles to many little what if

Wow dude! All over the place there, but I think I get ya. bad O2 would trip codes though man...

loudford · #9 (**permalink**) 09-03-2009, 09:05 AM

I had a similiar problem with my 03 5.4, poor gas no codes and only 60K. Finally threw a code for cylndr and I replaced all the plugs. They didn't look that bad but it was enough, after I replaced all is good. Mileage is up and throttle response is much better. Depending on you mileage it may be time? Before replacing the plugs I changed air/fuel/pcv valve that didn't help much.

GL

Lou

yosemitesamiam · #10 (**permalink**) 09-03-2009, 10:02 AM

Quote:

Originally Posted by loudford

I had a similiar problem with my 03 5.4, poor gas no codes and only 60K. Finally threw a code for cylndr and I replaced all the plugs. They didn't look that bad but it was enough, after I replaced all is good. Mileage is up and throttle response is much better. Depending on you mileage it may be time? Before replacing the plugs I changed air/fuel/pcv valve that didn't help much.

GL

Lou

Hey, thanks man! That is kinda what we deducted as well...just don't have the time right now to handle it. No codes by the way, no pendings, no nothin! Scanned it using my dad's equipment...shop grade scan tool. Oye Vey I say! Plugs she will be!