2003 Pontiac Grand Prix

Tiny
GONK24
  • MEMBER
  • 2003 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 136,000 MILES
My Grand Prix recently had the water pump go out. I changed that with no issue but now the car is shaking. It shakes at idle while still, the moment just before a stop, and when letting the car go forward without foot feed input. In park the shake goes away around 1500 rpm. While driving there is no vibration/shake whatsoever and it drives like a dream. Full power is there with no cutting out. It did kick a code which was for misfire in cylinder 3. I changed all plugs and wires and #3 is still kicking the code. The codes are always pending when read. I switched coils hoping the misfire would move with the coil but no, still #3. The shaking can at times be pretty strong. Along with that shake it has an exhaust chug keeping time with the shake.
Tuesday, September 15th, 2009 AT 10:36 PM

4 Replies

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Check the waterpump install again, look for any electrical connectors you may have missed, or ground wires that are not connected.

If car was running OK before waterpump install, then it is logical to assume something was not reconnected or a wire was pinched.
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Saturday, September 19th, 2009 AT 7:45 AM
Tiny
GONK24
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  • 3 POSTS
The water pump is belt driven and doesn't require and type of wires, plugs, or grounds. There's also nothing of that sort in the area of the pump. I've been able to trace the problem to a misfire in cylinder 3 at idle and very low rpm. Trying to get to the bottom of that now. Seems like there's too much fuel being dumped into the cylinder causing it to flood out at low rpm.
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Sunday, September 20th, 2009 AT 11:58 AM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Pull the #3 plug and hook to wire and use a calibrated spark tester, grounded to valve cover bolt.
Look for a blue snapping spark.

A weak spark could cause the plug to gas foul.

All I was suggesting with my previous post is that when changing a WP, you can sometimes (unknowingly) disturb wiring connections or spill coolant on them causing a bad electrical connection.
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Monday, September 21st, 2009 AT 9:16 AM
Tiny
GONK24
  • MEMBER
  • 3 POSTS
What would cause the weak spark? Ignition module? I have checked the coils by switching them around with no effect, but have not had the module itself tested.
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Monday, September 21st, 2009 AT 9:43 AM

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