Codes showing both banks "lean"
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Senior User
Joined: Oct 2006
Posts: 165
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From: Calgary, Canada
Codes showing both banks "lean"
99 f150, 4.6 occasionally sets check engine light, when I put the scanner on it it shows the codes for both cylinder banks "lean" (sorry don't remember the code #s). what can cause this code to be set??? Any ideas?? thanks
Hotshot
Joined: Jan 2004
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From: St Louis
This is NOT an O2 sensor problem. Do not waste your money on them.
This combo is almost always due to a vacuum leak, especially the elbows on the PCV valve hose. Other intake tract leaks post-MAF, and dirty/faulty MAF are also possibilities, although thay are well down the priority list.
Steve
This combo is almost always due to a vacuum leak, especially the elbows on the PCV valve hose. Other intake tract leaks post-MAF, and dirty/faulty MAF are also possibilities, although thay are well down the priority list.
Steve
Posting Guru
Joined: Oct 2005
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From: Louisville, Kentucky
Originally Posted by gregshively
you might want to check the o2 sensors in front of the cad. conv. my 97 had 1 bank to lean couldn't get it right replaced o2 sensor in front of cad conv no more probs.
Elder User
Joined: Nov 2001
Posts: 892
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From: Duluth, MN
It COULD be O2 sensors, yes. But the odds that both go bad and stay lean is remote. A single side lean code is more likely. Check fuel pressure too. Less then spec. pressure could affect fuel delivery and throw a lean code. But like everyone else ALWAYS states: dirty MAF, Vacuum/Intake leak, PCV elbow. If you can hook a scanner up and watch the O2 PIDS, and try to richen it out with propane to make sure the O2 sensors are working, then go from there. Clean the MAF with GOOD brake cleaner(We have MAG 1 at work) or better yet electrical cleaner, then check for vacuum leaks by fitting a propane bottle with a rubber hose and spraying it around the intake manifolds and vacuum hoses and watch for an idle change in the engine....
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Lead Driver
Joined: Sep 2006
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I will throw another wrench into the wheels.
The code does not mean the..engine..is running lean.
It means the PCM has leaned out the..fuel..tables so far that they are now out of range, hence the codes.
The 'un-accounted for air' going in makes the PCM richen up the fuel tables , then the OX sensors are the only way this condition is detected.
Fix the air leak!. It's not the OX sensors.
The code does not mean the..engine..is running lean.
It means the PCM has leaned out the..fuel..tables so far that they are now out of range, hence the codes.
The 'un-accounted for air' going in makes the PCM richen up the fuel tables , then the OX sensors are the only way this condition is detected.
Fix the air leak!. It's not the OX sensors.
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Senior User
Joined: Nov 2006
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when the truck is idling, spray some carb cleaner down all over the intake manifold(upper and lower-spray it up!!!), if it misfires or accelerates in RPM you have a leaky intake. Believe it or not that is how the guys at the dealership diagnose it. usually on any V style motor only 1 intake side leaks.... But its the plenum aka upper intake (almost like a precombustion chamber) and the plenum is sucking in too much air, you would have a lean code too. your PCM wants to see 14.7 air to fuel... anything whack and joe(the little guy inside your PCM) gets pissed off and sets codes. anything like too much air, too little fuel, both are gonna **** joe off!
Try the carb cleaner for starters, otherwise its probably a vaccuum leak.
Try the carb cleaner for starters, otherwise its probably a vaccuum leak.
