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Discussion Starter #1
Bank 1 and 2 lean on 97 F-150 w/5.4. Had my brother take it to the mech's, scanned it and got that. Figured it was prob a bad tank of gas...tank was full when i got home Thurs night and Sat is when it threw the code. Had been driving it all weekend pulling wagons, bouncing through corn fields, etc. Still ran fine. They suggested running the gas out and filling up again to see if it fixes it. Any other suggestions on what it might be? I really don't think it is the O2 sensors since it happened all at once. I didn't get the exact code # either. Heading home tomorrow again, we'll see what happens with it. TIA

Joe
 

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Our '99 5.4 F150 had the exact same codes two weeks ago. Wife and daughter filled the tank and went out of county shopping for about eighty miles. As they got near home, the cel came on and those are the codes I read. I speculated water in fuel, so I poured in a bottle of water absorber and cleared the codes. It has been way over a hundred-fifty miles and no cel yet. Maybe they had a lot of little misfires as the engine took in water/gasoline, that would have made the computer think they were leaning out.
 

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cheap start

A buck and a half for water absorber like Heet. Clear the codes. Verify that no spark plugs have water or antifreeze in the hole. Sometimes when an F150 drives through too much water during a rain, the cops will short out a little and those missfires make the computer think you are running lean. If no change after that, you might have a vacuum leak causing a missfire condition. Check the hose between the throttle body and firewall, then follow to its end (charcoal canistor) looking for rot and breaks. Bad oxygen sensors trigger their own oxy codes (several). I think maf wires are heated and self cleaning under normal conditions. Did you recently re-oil a cotton performance air filter? Too much will ultimately coat the maf wires, but that should lead to bad running you will really feel. Did you also check with the F150 sites first? Lots of those have your type of question routinely.
 

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Missfire = running rich. The computer may log a missfire code but it won't ignore the oxygen sensor data which will read rich with a missfire. Granted this only holds true if the oxygen sensors themselves are even working as they should be.

Bad oxygen sensors don't always trigger the code they are supposed to (generally slow response). They can read incorrectly with no clue as to what is wrong except decreased power and economy.

And a dirty MAF won't always make the car run like crap. It can cause subtle alterations to the fuel trim tables (hence running rich or lean, generally lean) and go as far as affecting transmission shift and TCC lockup schedules.
 

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Discussion Starter #7
Prob start with a bottle of heat and see how that works and I'll check for vac leaks. Truck is bone stock, farm vehicle, so no K&N to get the MAF extrmely dirty.
Thanks for all the replies.

Joe
 

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Misfires

Little missfires make the computer think it's running lean , and it will richen up the mix. So while the engine physically is "running richer", the extra air in the exhaust from occasinal misses makes the oxy sensors read "lean". Only little water-born missfires can do this. A cronic miss from any cylinder will trigger a missfire code. A huge vacuum leak will richen up everything so much that plugs will foul and then trigger missfire codes for themselves while some lean codes will also be set. Computers get lied to a lot, and they believe everything, truth or not.
 

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Huge vacuum leaks cause engines to run lean! Any vacuum leak is letting in extra air past the metering device, and this extra air is not factored into the computer's calculation for fuel and the car will run LEAN.

And misfires (of any degree) won't make the car run lean! Oxygen sensors read the content of oxygen in the exhaust, not "air". Plain and simple, if a plug has misfired then there is unburnt fuel being let into the stream of exhaust gasses. This unburnt fuel causes less oxygen in the exhaust stream, and if the sensor works it will read this as running rich. Conversely, not enough fuel causes an excess of oxygen in the exhaust stream, and this reads as lean. The computer doesn't "think" one way or another. In closed loop, the oxygen sensors tell the tale, and if everything is working as it should it won't read incorrectly.
 

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Discussion Starter #10
Brother filled it up w/some better gas, was near empty. Reset EEC and he said it came back on afterwards. Haven't had a chance to put any HEAT in it, but I cleaned the MAF with some electric contact cleaner tonight and reset again. They hooked it up to a smoke meachine at the mech's and found no vac leaks, which is good. I will see if cleaning the MAF helped any tomorrow, but I still have a couple weeks to figure it out before I take it back to school w/me.

Joe
 

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An oxy sensor reads oxygen content only, we are all correct. A few missfires let that cylinder's air pass thru unburned. The oxy sensor reads the unburned air and believes this to be running lean, and therefore richens up the entire mix for that bank. If there are some misses on both banks, then both sides report a lean condition , and the injectors are richened up. If the missfires never cease, as in a fouled plug or contaminated fuel , those missfires will always allow oxygen in the exhaust to be read as running lean. The computer can never make the correct trim. Finally, when the fuel trims are maxed out, you can get lean bank one and two codes even though the engine is physically running richer.I think we are all saying this, aren't we? A lean bank one and two code then can really be that if the metered air is missadjusted by the maf, or it can be excessively rich but missread by the oxy sensor if missfire induced. A big vacuum leak will cause major missfires, you will really run lean at first, then the computer will ultimately overcorrect to over rich and the motor will run so bad you will struggle just to get down the road, but you'll get lean codes set by the oxy sensors. I think it's water in the fuel today. Maf tomorrow. Computer codes are a lot like interpreting the bible,don't you think?
 

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Edit: After a lot of research stemming from the information from svtbird88, I have determined that edman is correct. Oxygen sensors can't read the "fuel content", only the air that enters and exits the cylinder. I stand corrected and apologize for my ignorance.
 

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Discussion Starter #14
Even though I can detect no major misfires, it runs good, I think I am going to change the plugs. I bought it w/90K on it, and now has about 118K on it, and I have never changed them. I'm just dreading doing it though...there isn't much room. I think I will change the fuel filter and do the other minor tune up items as well. Still trying to run a couple tanks of good gas through it, kind of hard when I only drive it on the weekends. Hopefully I can get this done this next weekend and repot back on what's going on.

Joe
 

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i didnt know vacum leaks could set off a code
 

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Maxion$Mulla$ said:
i didnt know vacum leaks could set off a code
If big enough they have the potential. Small ones will normally just make the car run weird, idle high, lose power, etc. But with a big enough leak, the car will hardly be driveable, so you can't trust any codes at that point.
 

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what happened to my daughter's '96

My daughters 4.6 LX had two problems at the same time. I feel bad for all the costs she incurred, even though I did all the free labor. Two and a half months ago, she began her five mile drive home from work with the following conditions ( all seen as hindsight after the fixes ) : her driver's side sparkplug boot became more contaminated with coolant , and her primary vacuum line from the back of her throttle body was so brittle that it ruptured open. She said she could barely get past forty, vertually flooring it to get home. By the time she made it here, her cats had melted and were rattling in their shells. The engine clearly was running on seven or less cylinders. I pulled a few plugs and many were soaked with fuel. Her code was a missfire at one cylinder ( a fuel fouled plug) and a lean code for one of the sides ( forgot which). The exhaust reeked of gasoline smell even with a lean code. That's when I realized you have to read between the lines when it comes to understanding cel codes. Her periodic miss from the coolant-short riched up her mix to start with, and then her vacuum line rupture compounded it by trimming the mix richer still. Finally, several plugs became gasoline fouled , all the while the computer was thinking it was leaner still. She just passed smog this past Saturday after I found the worn hose that set her p1443 code. She is cel-free now, and I finally have time for my own '97 LX again.
 

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Discussion Starter #18
Well, tonight I got around to start changing the plugs...what a nightmare. I got the front two on each side, but the back ones...well, lets just say there are people who get paid to do that, and that's who will be doing them. But both sides, the plugs were white. Also changed the fuel filter and poured the gas out of it, it was brown. Prob never been changed before. Reset it computer, I've got some driving to do tomorrow, I'll see if the CEL comes on again. It runs good yet, so I'm hoping the fuel filter took care of things.

Joe
 
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