How can you tell if you have a bad coil pack? Does it set a code? 2000 tahoe 4.8L?

it can set and usually does set a code po300-po308 depending on the cylinder that is misfiring. only has to detect the problem once to set the code in pending codes and twice to set it as an active code to turn the MIL on. scan the car and see if there is a code...like I said the light doesn't have to be on for there to be a code. you can use a spark tester and plug it into the coil to ground to test it or use a secondary ignition scope to determine if its bad. or use scan tool data and do a cylinder contribution test. but most of these tests can only be done with expensive tools and with somebody trained.

to add,

on the surface, i'd be Qing the anit-knock sensor.

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but in the dark of night, engine running, have a look see. note any arcing. look closely. starting at the coil pack all the way to the plugs.

if this is a coil atop plug config, could be arcing under the coils. can't see that.

in any event,

there would be at least an intermitant issue. in that case, the CEL may not remain lit. or just flash. even if you didn't notice any CEL, there should be a code stored. retrieving that info should narrow down what's going on if a visual doesn't turn up anything.

Spark plugs with gaps that have burned too wide or short pig-tail ignition wires which have been installed for ever will cause any one of the individual ignition coils to overheat and fail do to high electrical resistance.