I have a 1994 Pontiac Grand Prix SE, 3100 v6. She developed a miss. Thinking
she needed a tune up, I replaced the plugs, and the wires. No change, after
testing the ignition system, and finding nothing.. I sent her off to a
mechanic. The mechanic replaced one coil pack, and said the previous was bad
and the spark plugs, but the miss was still there. They did a compression
check, and all seemed ok. They wanted to replace all the injectors, after
$250.00 and what seemed like the throwing of parts, I took the car to a
family mechanic. He's a good guy that knows his stuff, but he's stumped. I
have one cylinder that the spark plug is fuel fowled. Going from the
previous mechanics suggestion, we replaced the fuel injector. Nothing
changed. We have good spark to all cylinders. My family mechanic thinks that
maybe the cam lobe could be bad, allowing compression to check out, but not
allowing fire to ignite the fuel. We are going to remove the valve cover and
see how the valve movement goes, but again if that isn't the trouble, he is
stumped. Does anyone have any other ideas about what could be causing the
problem?

clevere wrote:

It wasn't real common on your generation of 3.1 engine, but you
might want to check for an intake manifold gasket that is leaking
vacuum internally. This was much more common on the older
engines that used a paper gasket. You can check this quite
easily by simply removing the oil filler cap and then spraying
something like brake cleen or throttle body cleaner down
into the valve cover/lifter valley area. If you have some sort
of vacuum leak inside there, you will notice a difference in how
the engine runs. This is really just a guess.

Ian

had one with similar problem and it was the wire from ignition module to
crank sensor