2006 Pontiac Grand Prix engine misfire. V6 3.4L.
The check engine light is on.
I replaced
spark plugs and new wire harness,
tranny flush.
Question:
My check engine light is on. This started when I
set my cruise one day and it started to chug
immediately so I shut cruise off and engine light
was flashing then stayed on. So put it in computer
and it said cylinder 4 misfire so I changed all the
plugs and wires and it continued to do it.

I took it to shop and got a tranny flush and had
them check why engine light is on and they said it
was just a malfunction so they reset it and I left
there and my car chugged and light came back on.

The chugging happens when I am gradually
accelerating and my RPM gauge is right above the
2. Not sure what's wrong any ideas?
Answer:
An engine misfire under load like you describe is usually
caused an
ignition system component. I would assume you
have a code P0300 or P0302.

Accelerating from speed puts a big load on the ignition system.
Most common cause for this is the spark plugs or plug wires.  
Since you replaced them, that of course was not it.

Next you need to look closely at the ignition coil towers. If there
is any corrosion, that would be the cause of your misfire. See
picture below. Also look for a crack between the towers.

If that checks out OK, then next would be to diagnose a
possible
fuel injector problem. Either the #2 injector is not
firing, is restricted, or has no signal. Using a test light to check
for pulse signal is needed. If it has pulse, then a flow test would
need to be done. A restricted injector will usually only cause a
misfire at idle, but can also when accelerating.

If all this checks good, then another possibility that is not as
common is a rocker arm coming loose. This can happen if the
lower intake manifold gaskets were replaced in the last few
months. Improper torque can lead to a rocker arm bolt coming
loose from the cylinder head. This can also cause an engine
ticking noise.
2006 Pontiac Grand Prix Misfire And Chugging
A good GM ignition coil makes engine run smooth and no hesitation.
Corroded GM engine ignition coil and spark plug wire causes misfire code p0300

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