Why does the engine on 98 chevy blazer skips and shake in park and driving ? Could it be spark plug wires are bad ?

could be a sensor...have it scanned...sounds like the problem....and good luck.

My initial thought is that you have no spark in one cylinder. This could be from a bad spark plug or other ignition component failure. Have the spark plugs ever been changed? I would rule this out first, as they are inexpensive, and also under more stress than any other part of the ignition system. If the problem persists, then it's time to look at the spark plug wires or ignition coil.

Start the car and open the hood when it's dark. Do you see/hear sparks coming from the plug wires? Another inexpensive place to start looking.

sounds to me like your cat is pluged.

Spark plugs and wires,
Bad or leaky vacuum line
Bad 02 sensors, (check engine light would likely be on)

If it doesn't do it at idle, then motors mounts should be good and the problem is one of the listed above.

bad relay or a bad wire

If your engine timing is good, (meaning the cam is timed to the crank, and distributor) and you have spark and fuel, your engine will run. Try a compression test, and back up and re-test fuel and spark. Make sure the spark works with a HEI spark tester. (Coils can go bad and give a weak spark)

could be a bad plug even know they are new one might be bad , first check in the dark for any arcing (blue sparks) coming from wires might be a split in one of the spark boots ,make sure on there good,also a chance you put wire to wrong cylinder

low compression - worn spark plugs and wires - weak coils-clogged fuel filter.

Does it crank the engine ? If not take a look at the starter connections and the starter.Replace the starter if nessesary.
Ok, now that you got the most common problems out of the way, you should check for spark at the spark plugs. Remove a spark plug and attached to the wire. Get a good pair of rubber gloves and put the thread of the plug to ground and crank the engine. The spark plug should spark a bluish spark. If it has an orange spark the spark plug or wire may be bad. if it does spark fairly good.

Check the fuel pump. if it has an electric fuel pump you should hear it when you turn the switch to on. It is a whirring sound. if you can't hear it. the Pump is bad or the shutoff valve turned off the fuel system. Check it to see if the button is up. If it is then the valve clicked off. Press it down. If it is down and there is no fuel the fuel pump is bad.

If it is a mechanical pump, take off the hose to the carb if it does have one. crank the engine . It should pump gas right away.

If it does have spark or fuel to the sytem, then it is a sensor or other problem.You will have to get a trouble code for it. to narrow everything down.

Check the timing belt or chain to see if it is still good and tight. If it is not your timing belt or chain skipped or cut off. you will have to replace it.

I hope you can get some help from this info . good luck

Look for a bad coil pack. If you have the bank of three coils on the front passenger side of the motor, it is possible that one of them is going bad. This can be an intermittent problem since it failure is frequently heat related, and may not show up until the car is all heated up. It is simple enough to change one of these if you can figure out which one it is. There is a little device ( Spark detector) that can sense the sparks inside the wires. Get one and hold it close to each wire... away from the coils. The wire, that does not make the spark detector light up...is coming from the bad coil. (It is also possible that a spark plug wire is bad instead.) Good luck. Chip