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1998 Pontiac Grand Prix Shake on start-up after sitting ove

Tiny
ANDERP70
  • MEMBER
  • 1998 PONTIAC GRAND PRIX
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 148,800 MILES
2 days ago I had new wires and plugs installed due to misfires on cylinder 2 under load. Plug on C2 was burned at wire connection, most likely arcing. Prior to having the wires and plugs done, the car would shake for 10-15 seconds, not violently, but noticeably after sitting overnight. This was a recent development that has happened before but gone away on its own. RPMs would remain at normal idle range, no SES light. Felt similar to a misfire while driving. Now that the plug/wires are replaced, shaking continues on start up but I can't get it to misfire under load, and I've tried. Mechanic did mention small amount of coolant in cylinder near the bad plug. I have no coolant loss, no overheating issues, no oil issues, no smoke in exhaust.
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Thursday, September 10th, 2009 AT 10:01 PM

3 Replies

Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
You may have the beginning of a (the common) lower intake gasket failure. Do a compression and leak down test on all cylinders.
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Friday, September 11th, 2009 AT 2:46 AM
Tiny
ANDERP70
  • MEMBER
  • 6 POSTS
Already had the intake gasket replaced about 4-5 years ago. Discovered that when there was oil in the coolant. Hasn't been a problem since. Anything else it could be? Head gasket maybe. That's what I thought, but I have no other symptoms and my mechanic said if it is the head gasket, I'll know within a couple weeks b/c it will fail completely.
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Friday, September 11th, 2009 AT 10:52 AM
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Your mechanic is correct. But a compression and leak down test will confirm any type of head gasket or intake gasket failure.
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Friday, September 11th, 2009 AT 4:55 PM

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