GMC Troubleshooting Questions? Ask a Mechanic for Answers
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Is this cylinders 1,3,5 and 7 misfiring instead of #4 cylinder by chance?
Let me know so we can continue,thanks Pete
O.k.,your model has 2 catalytic converters as shown in the diagram below.One right below the manifold pipe connection on each side of the engine.I suspect the drivers side is restricted.This commonly causes misfires with all cylinders under load on that side of the engine.If you have not had an exhaust back pressure test done this needs done.You can usually rent a back pressure tester from a local parts store.Remove the oxygen sensor before the catalytic converter on the drivers side,thread in the tester.Start the engine and rev it up.The back pressure should not exceed 1.5 psi at any rpm range.If it does then the catalytic converter needs replaced.
If you have already tested this and found it to be o.k. and not the issue here let me know but I do suspect this is the cause as this is most common for misfires on one bank like this here.
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