I found a short article in a trade magazine relating to the 4.7L in the
Gr. Cherokee, soon to be in the DAK. I cant find the page I ripped out
and brought home, but thought I'd share the info to be filed away for
future reference.
Apparently, and for what reason I'm not sure, the 4.7L is calibrated
to run rich at idle when the transmission is in Park or Neutral. Once
the transmission is shifted into a forward gear, the computer changes
the mixture so that emissions will be acceptable.
If you go in for an emissions test and your state doesnt use the new
dyno type, "IM240" test, but uses the old test, they will be running the
vehicle in Park or Neutral, and you are almost guaranteed to fail. This
reminds me of Ford 4.9L. Many built in the 80's ran rich at idle, and
you had to shut them off and restart them when you pulled into the test
center to make sure you didnt automatically fail.
Patrick
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