At 08:10 PM 4/3/02 -0600, you wrote:
>For quite some time my 99 R/T has done a peculiar thing. If I coast down
>from highway speed like approaching a red light and the light turns green
>before I come to a stop say from about 20-30 mph and I punch the throttle
>hard it may backfire into the tb one time then takes off like normal. Has
>anyone had that happen? It only does that occasionally and I cannot
>demonstrate it to anyone because I never know when It is going to happen.
>Jim in Waco. My truck has 41k miles on it. 180 thermostat, 3923 plugs,
>high flow cat. I never get a check engine light.
Hi, Jim.
It hasn't happened to me as yet. I do coast down for lights but it usually
in city and not highway situations.
For a backfire into the intake manifold and thus into the tb to happen, the
spark
must be meeting with a not fully-seated intake valve on the compression stroke.
When coasting down, the pcm goes into open loop and reduces pulse width
to lean the a/f mixture. Under certain rpm and closed throttle position
conditions, the pcm will cut off fuel injection until idle speed is reached.
I'm guessing that fuel injection cutoff has occurred and on the odd occasions
after you've punched the throttle hard, ignition timing, unseated intake valve
and a still lean condition just "happens" all at once to cause the backfire
in the tb.
Bob
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