engine cods
Postmaster
Joined: Oct 2009
Posts: 3,432
Likes: 7
Typically these codes are set when the computer has attempted to correct a lean condition and it has hit a critical cutoff point. Common causes include: low fuel pressure, vacuum leaks, faulty MAF sensor, misfires, and major exhaust leaks. Lets start with the basics.
Intake leaks are probably the most common. These can come from a number of sources. The PCV valve can be stuck open, vacuum hoses can be cracked, broken, or disconnected. In addition, the seal in the upper intake manifold can have shrunk or cracked. A ruptured brake booster can also be a leak source, though you will most often notice the brakes to be hard to press if this is the case. Any leak of any kind between the MAF sensor and the intake valves can contribute to these codes.
Fuel delivery problems can't be ignored either. If the fuel pump is cutting out or has a low output or the filter is plugged, or the regulator is faulty, you can get a lean code. The fuel filter is a maintenance item, since you just bought the truck, make it a policy to replace all fluids and filters. Test the fuel pressure with a gauge, and route it so that you can see it while driving. If the pressure ever drops below minimum specs (I'm not sure what those are for your year), then you probably have a weak pump. If the pressure is constantly low, or constantly high, the pressure regulator is bad.
Misfires result in unburned oxygen entering the exhaust. The computer may not always detect the misfire, but the extra oxygen is picked up by the O2 sensors, and the computer will attempt to correct the reported lean condition by adding more fuel. Since you just bough the vehicle, unless you have evidence to suggest otherwise, assume the plugs have not been changed, and replace them with Motorcraft or Autolite double platinum. If you vehicle has traditional wires, replace them with Motorcraft.
Typically a faulty or fouled MAF will set a MAF related code. Just to be sure, you should try cleaning it with a specialized MAF cleaner. If that helps, the MAF is part of the problem. If it doesn't restore the LTFT to within 5% with a simple cleaning, the MAF needs to be replaced.
Exhaust leaks rarely contribute to this condition, though any that are found should be corrected. An exhaust leak in the manifolds, or in the pipe ahead of the primary O2 sensors can adversely affect their accuracy. O2 sensors are also maintenance items and should be replaced on approximately 80,000 mile intervals. They will pay for themselves in fuel savings, and by sparing you the expense of replacing catalytic converters. In and of themselves they will not set a lean code, but if they are old and worn out, they can contribute. Replacing them can bring the calibration enough in line to correct the lean codes.
After replacing the required part(s), the vehicles long term fuel trims should be checked to ensure the issue has been fully corrected. A smoothly running vehicle will have a fuel trim within 5%.
Intake leaks are probably the most common. These can come from a number of sources. The PCV valve can be stuck open, vacuum hoses can be cracked, broken, or disconnected. In addition, the seal in the upper intake manifold can have shrunk or cracked. A ruptured brake booster can also be a leak source, though you will most often notice the brakes to be hard to press if this is the case. Any leak of any kind between the MAF sensor and the intake valves can contribute to these codes.
Fuel delivery problems can't be ignored either. If the fuel pump is cutting out or has a low output or the filter is plugged, or the regulator is faulty, you can get a lean code. The fuel filter is a maintenance item, since you just bought the truck, make it a policy to replace all fluids and filters. Test the fuel pressure with a gauge, and route it so that you can see it while driving. If the pressure ever drops below minimum specs (I'm not sure what those are for your year), then you probably have a weak pump. If the pressure is constantly low, or constantly high, the pressure regulator is bad.
Misfires result in unburned oxygen entering the exhaust. The computer may not always detect the misfire, but the extra oxygen is picked up by the O2 sensors, and the computer will attempt to correct the reported lean condition by adding more fuel. Since you just bough the vehicle, unless you have evidence to suggest otherwise, assume the plugs have not been changed, and replace them with Motorcraft or Autolite double platinum. If you vehicle has traditional wires, replace them with Motorcraft.
Typically a faulty or fouled MAF will set a MAF related code. Just to be sure, you should try cleaning it with a specialized MAF cleaner. If that helps, the MAF is part of the problem. If it doesn't restore the LTFT to within 5% with a simple cleaning, the MAF needs to be replaced.
Exhaust leaks rarely contribute to this condition, though any that are found should be corrected. An exhaust leak in the manifolds, or in the pipe ahead of the primary O2 sensors can adversely affect their accuracy. O2 sensors are also maintenance items and should be replaced on approximately 80,000 mile intervals. They will pay for themselves in fuel savings, and by sparing you the expense of replacing catalytic converters. In and of themselves they will not set a lean code, but if they are old and worn out, they can contribute. Replacing them can bring the calibration enough in line to correct the lean codes.
After replacing the required part(s), the vehicles long term fuel trims should be checked to ensure the issue has been fully corrected. A smoothly running vehicle will have a fuel trim within 5%.
Elder User
Joined: Jan 2008
Posts: 589
Likes: 0
From: Stockton Ca.
Try to remember to let those who want to help you know what engine you have.
That being said if your truck has a V8 most of the time those codes are caused by the PCV lines rubber boots failing, usually it's the boot on the back of the intake.
Good luck.
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