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