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Re: lean mixture fault code on "new" engine Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 14 May 2008 11:57:52 In Reply to: lean mixture fault code on "new" engine, Jeremy, Tue, 13 May 2008 21:55:24 Members do not see ads below this line. - Help Keep This Site Online - Signup |
That code is indeed a lean mixture fault. Remember how the control system works - it estimates the amount of fuel needed from measuring the airflow through the AMM. It then fine-tunes that with the O2 sensor signal.
If the O2 sensor says the mixture is lean, the ECU adds fuel until the O2 sensor says the mixture is right. But it will richen the mixture only so much; if the O2 sensor is still reading lean, the ECU has reached the limit of it's authority to richen the mixture, and it declares a "Lean" fault.
So you'll get this fault if (1) you're running really lean, or (2) the O2 sensor is lying, and it's saying lean when you're really runnigh rich.
Step 1 - pull the spark plugs. Do they look rich or lean? If they look lean, then the O2 sensor is telling the truth. You can be running lean due to a vacuum leak, low fuel flow/pressure, etc. If the plugs look rich, then the O2 sensor is lying. Or just not hooked up. The O2 sensor output is near 0 volts for lean, and near 0.9 volts for rich. Notice that lean looks the same as the wire shorted to ground or possibly an open.
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