Check Engine Light
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New User
Joined: May 2001
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Check Engine Light
For a couple of years now, the light has been on. I can clear it for a while, but it always comes back. The codes say "left bank lean", "right bank lean". I've changed the fuel filter, but it didn't help.
Any ideas? O2 sensors bad?
1996 F-150, 4.9L, automatic, E4OD
Any ideas? O2 sensors bad?
1996 F-150, 4.9L, automatic, E4OD
Postmaster
Joined: May 2002
Posts: 3,241
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From: Broken Arrow, OK
Codes 171 and 174 (lean bank 1 and bank 2, respectively) are caused when the MAF reading doesn't corresond to the fuel trims and O2 sensor reading that the computer is expecting to see. The most common causes of the codes are contaminated MAF sensor element and vacuum leaks. You can clean the MAF element with a Q-tip and some rubbing alcohol, but be very careful because the element is very delicate. Vacuum leaks can be a royal pain in the butt. I would check all the obvious vacuum lines, and if you don't find anything take it to a shop and have it smoked out. They will probably charge you $25-30 to smoke it, but then you will know where the leak is. The PCV system is the most common vacuum leak to cause the problem, but leaks between the MAF and throttle body are common as well. Fuel supply issues can also cause these codes, but that isn't common.
These are two of my least favorite codes to see when I plug in the scanner. Have fun.
These are two of my least favorite codes to see when I plug in the scanner. Have fun.
Thread Starter
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New User
Joined: May 2001
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OK. I pulled the housing with the MAF sensor, and carefully cleaned both elements with alcohol on a Q-tip. I did see some residue on the Q-tip after cleaning.
I also had suspected I had a vacuum leak for a while (just sounded like it). I pulled the PCV valve and found that it had two connections on the side. The larger one had the hose connected to it. The smaller one had a 1" piece of hose with an open end on it. The new valve came with a cap for the top connector. I looked at the vacuum routing under the hood and it only shows one hose to the PCV valve, so I capped it. I seem to vaguely remember the last time I changed it the short hose was on there, so I stuck the cap in the end of the hose (maybe). Doesn't seem likely but maybe it came out. Anyway, it may just be in my head, but I don't notice what I thought was a leak as much as before.
I'll post back if the CEL comes back on.
Thanks for your help.
Now if I can figure out the tapping noise I have under load. Think it's some kind of exhaust leak, but don't really know how to find/repair it.
I also had suspected I had a vacuum leak for a while (just sounded like it). I pulled the PCV valve and found that it had two connections on the side. The larger one had the hose connected to it. The smaller one had a 1" piece of hose with an open end on it. The new valve came with a cap for the top connector. I looked at the vacuum routing under the hood and it only shows one hose to the PCV valve, so I capped it. I seem to vaguely remember the last time I changed it the short hose was on there, so I stuck the cap in the end of the hose (maybe). Doesn't seem likely but maybe it came out. Anyway, it may just be in my head, but I don't notice what I thought was a leak as much as before.
I'll post back if the CEL comes back on.
Thanks for your help.
Now if I can figure out the tapping noise I have under load. Think it's some kind of exhaust leak, but don't really know how to find/repair it.
