Hey all...I know it has all been heard before. 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
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99 Exped XLT 4x4 5.4L
Frisbeetarianism is the belief that when you die, your soul goes up on the roof and gets stuck.
you may have latent codes that aren't tripping the PCM enough to trigger a CEL.
Also, your description is pretty indicative of a O2 sensor, or that Coolant Temp Sensor mentioned. If you have a higher mileage motor, you might be burning a bit of oil or some blow-by. That gets into the exhaust and can foul the sensor
1st thing I would do is pull codes. See what is going on from the PCM perspective.
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you may have latent codes that aren't tripping the PCM enough to trigger a CEL.
Also, your description is pretty indicative of a O2 sensor, or that Coolant Temp Sensor mentioned. If you have a higher mileage motor, you might be burning a bit of oil or some blow-by. That gets into the exhaust and can foul the sensor
1st thing I would do is pull codes. See what is going on from the PCM perspective.
Interesting. I'll need to stop by a shop and see if there are any pending codes. Thanks...and yes, I'm burning about a quart every 1,000 to 1200 miles or so.
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99 Exped XLT 4x4 5.4L
Frisbeetarianism is the belief that when you die, your soul goes up on the roof and gets stuck.
Interesting. I'll need to stop by a shop and see if there are any pending codes.
If you have an exhaust leak ahead of the upstream O2 sensor, in between the exhaust pulses it will pull air into the exhaust. The O2 sensor will see the excess oxygen and comand that bank rich to try and eliminate the extra oxygen.
Or a vacuum leak in ONE intake runner will do the same thing. (Since the O2 sensor can't distinguish WHICH cylinder is lean, only which bank is lean, it will richen up the whole bank to try and compensate.
If the shop can read pending codes, they should be able to read the fuel trims. Have then compare the STFT and LTFT at different engine speeds. Bank 1 and 2 fuel trims should be somewhat similar. (IIRC, the PCM maintains 9 different fuel trim blocks for various engine loads/rpms.) Long term fuel trims should be under ~12%; if it gets above 20% the PCM will set code P0171 and/or P0174).
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Jim in Central NY
'79 2WD F-150 Lariet w/302,4spd OD, 228,965 mi. (Original Owner!)
'02 4X4 Navigator w/5.4L DOHC 32v Intech V-8.
If you have an exhaust leak ahead of the upstream O2 sensor, in between the exhaust pulses it will pull air into the exhaust. The O2 sensor will see the excess oxygen and comand that bank rich to try and eliminate the extra oxygen.
Or a vacuum leak in ONE intake runner will do the same thing. (Since the O2 sensor can't distinguish WHICH cylinder is lean, only which bank is lean, it will richen up the whole bank to try and compensate.
If the shop can read pending codes, they should be able to read the fuel trims. Have then compare the STFT and LTFT at different engine speeds. Bank 1 and 2 fuel trims should be somewhat similar. (IIRC, the PCM maintains 9 different fuel trim blocks for various engine loads/rpms.) Long term fuel trims should be under ~12%; if it gets above 20% the PCM will set code P0171 and/or P0174).
BINGO DUDE! I do have an exhaust leak...the exhaust manifold on the passenger side is leaking and getting worse...I actually ordered parts (gasket kit, stud and nut kit) for that side this weekend and will have it tomorrow.
Typically the leak has only been on cold engine...once the system heats up it would go away. Didn't think much of it in this manner. One day we were coming down a steep incline, 2nd gear going less than 25mph, I could hear it, fully warmed. That's when I decided it was time to do something about the leak...
Thanks man...I'm going to try and forget about it until after I get the leak fixed.
Question about the intake runner leak probability though...audibly my exhaust noise is about equal up top as it is below. In the off chance I have an exhaust leak (which I've visually confirmed 3 studs sheered off on the passenger side manifold) AND an intake runner leak...how do I trouble shoot and confirm the intake runner?
Thanks again man!!! Nail on the head me thinks!
Sam
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99 Exped XLT 4x4 5.4L
Frisbeetarianism is the belief that when you die, your soul goes up on the roof and gets stuck.
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