Auto Service Professional

APR 2016

Magazine for the auto service professional

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17 | April 2016 Circle 105 on Reader Service Card It's tempting to think these symptoms indicate a vacuum leak or low fuel pressure, but this is an article about mass air fow sensors (MAF), so at this point you already know that's the problem to be considered. The clue is in the fuel trim numbers and the lack of power at WOT. Fuel trim is negative at idle, the oppo- site of what you would see with a vacuum leak, and it changes to positive at higher speed/load but the oxygen sensor readings still indicate it's running lean. That could be caused by low fuel pressure, but the engine continues running smoothly even at WOT. So the question is, if this really is a bad MAF sensor, how can it have such a dramatic affect on fuel delivery and engine performance without setting a code? Before exploring that question, let's review how a MAF sensor works. Description and operation Although there are some differences, electronic MAF sensors all work on the same principle. A resistance-calibrated wire is mounted in the engine's intake airfow Powerplant

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