Tips for diagnosing system lean codes presented by
Auto Service Tech training today for tomorrow's challenges
www.autoservicerech,com the majority of "system lean" codes seem to be the result of vacuum leaks. Any air entering the engine DOWNSTREAM of the MAF will result in a lean condition. Of course, this in not the only possible cause. Here's a method that works on and will quickly tell you if unmetered air is your problem. First, start the engine and monitor and monitor short and long term fuel trims at idle.
Now do the same with the engine running, no load, at 2500 rpm. If fuel trims at idle are correcting to limits for the lean condition, but are more normal at higher rpms, there is unmetered air getting in. And the best way to find it is with your EVAP system tester... smoke function! Case in point... a jaguar with unmetered air getting in. visually, there is no fault found. Another tech tried the old "carb spray" trick without success. Let's add smoke by connecting the EVAP tester to the intake.
Where there's smoke, there's air getting in! Let's pull the plenum and take a look... this simple rubber elbow connected the crankcase vent line to the separator... not visible or accessible with the plenum installed. With everything back together, fuel trims will tell us if we were right. Now short term is shifting the other way at idle.
And that's OK for a quick verification of the repair... but always reset the adaptive (KAM) memory when repairing fuel trim codes to prevent new problems for you and your customer. Hope you enjoyed the presentation!
Auto Service Tech Training today for tomorrow's challenges www.autoservicetch.com
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