1998 GMC 1500 Misfire


Asked by Aug 17, 2017 at 04:37 PM about the 1998 GMC Sierra 1500

Question type: Maintenance & Repair

After taking a 3 hour round trip in June, my truck began to misfire on the way
home, so I had to keep it revved to keep it started.  Initially, we did a full tune
up (spark plugs, plug wires, cap, rotor, oil, antifreeze, etc.)  This didn't fix the
problem and it turned out to be a cylinder 7 misfire.  The head was removed
and reviewed and no cracks were noticed.  It was put back together and ran
smooth until a couple weeks ago when it started misfiring heavily on the first
drive each morning.  It didn't seem to do it as much after that first drive each
day.  We replaced the plug wires and spark plugs thinking it may be defected
parts.  Nonetheless, it was not.  Cylinder 7 continues to misfire based on the
spark plug residue.  Please give me any and all recommendations.

2 Answers


Gasket not sealed in the area of #7. When heats up it seals. Look this up on these gm products. Manifold gasket?

1 of 1 people found this helpful.

What does the spark plug electrode look like? Wet and oily? Worn rings or valve guide seals. Dry black fluffy deposits? To much gas. Clean and wet? Leaking head gasket. Dry and white? Too little gas or leaking intake manifold. HTH. -Jim

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