Ford F150 with 4.2l 6 cyc. with 5 speed. Can not stop getting these codes. Mostely get 1074 lean on bank 2 but sometimes get both. So far I’ve done O2 sensors fuel filter. Do I have a leaking intake? 103000 miles.
The DTC P0171 and P0174 do indicate that both banks of the engine are running lean. That’s what the original oxygen sensors were telling you. Didn’t you believe them? If someone had looked at the voltages from the oxygen sensors, they could have determined if the oxygen sensors were telling the truth, or not.
An engine can be lean from two causes: too much fuel; or, too much air (fuel/air mixture ratio). Let’s say the fuel delivery is ok, where could extra (unmetered) air get into the cylinders? One place could be a leaking, cracked, or damaged air intake tube, or poorly sealing intake manifold. Another, an egr valve stuck open. Another, an idle air control valve stuck open.
Besides actual extra air, some sensor may be mistaken, such as the MAF (Mass Air Flow) sensor, a coolant temperature sensor error, an air temperature sensor error, etc.
The right hands, with a scan tool, can diagnose this.
check the PCV hose for cracks.
So you have assumed that I didn’t check the O2 sensors but I did, and the driver side rear showed to be defective (lean bank 2, the most frequent code) That’s the only one I replaced. This led me to think that I had solved the problem. But the code came back. Also, every so often I’ll get a lean bank 1 code just to mix things up.
I’m not sure I understand your comment about too much fuel causing a lean condition. To much fuel would give you a rich condition.
The reason I asked about the leaking air intake is because the engine has a plastic air plenum that supplies the intake. I guess Ford thought this would save a little weight on the engine? The only thing I can tell from reading about this is that it saved some engineer’s job by having to design a new intake on later models? They appear to be problematic at best and a down right pain in the butt at worst. I have checked for leaking vacuum hoses, I even hooked up a propane cylinder to a hose and waved it around all of the vacuum hoses and around the intake. The thougt being if I had a vacuum leak the engine would suck in the propane and increase the idle for a second or two while the computer adjusted. I was not sure this would work on a computer controlled engine or not. It was a big help in finding EGR valve leakes in the 80’s.
It would be helpfull if you could give me a list of all the of the sensors I should have checked out by the “right hands”. I want to at least sound knowlegable about this stuff when I go to the garage. That way they will be less inclined to try and get one over on me. If you get my meaning? And it may accually save me some money!
“…too little fuel, or too much air” would be correct. “Too much air” is unmetered air (by the MAF) which gets to the cylinders through any means. The wrong pcv valve, with excessive flow, is one way. A brake booster vacuum to a ruptured booster diagram, is another. An egr valve which is open too long, is another.
Use a vacuum gauge, on the intake manifold, to determine is there is a partial loss of vacuum. The lower vacuum could be from a leak.
The MAF could be telling the ECM that there is less air flow than actual. Temperature sensors which indicate higher than actual are another possible cause. Low fuel pressure, or flow, is another.
A scan tool would be used to look at the values from the sensors and actuators to determine if they are in correct ranges. The judgement, and knowledge, are in the mind of the scan tool operator, NOT in the scan tool. It’s just a dumb machine.