Question about 1999 GMC Yukon

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The engine has a skip.i have replaced the plugs.

The engine has a skip.i have replaced the plugs. i had the engine scanned,and it showed the 3 and 5 cyls are where the miss is occuring.what is best guess, cap, rotor, plug wires or head gasket? engine is a 5.7 gm with 160K .

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It is possible that the head gasket has blown between 3&5 cylinders, a leakdown test would confirm this, remove both plugs, put air to one, if you hear it leaking out the other, this is it, it should be at or close to TDC on one of the cylinders to have all valves shut for testing. Hope this helps, I know it is never good news when someone suggests you have a major engine problem,,, that is why a thorough test is allways the best plan!

Posted on Apr 27, 2010


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  2. the spark plugs all 4 must spark, not just one.
  3. the CEL lamp must turn on key on or fuses are blown.
  4. connect scan tool,
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  13. ill stop at fueling,,, you need a fuel pressure gauge next..
  14. btw, wide open cranking clears floods.

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How to replace spark plugs. Engine seems to skip?

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This will sometimes show a Code 401 and all you need to do is clean it. You can save yourself some work. If the scan guys think it needs plugs they will show you what you need. Remember to gap them if you do replace them.

I think this is the best thing to know whats wrong before you start taking things apart.

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