My dash keeps reading reduced power

Is the same cylinder causing the problem? If so take a close look at the spark plug for fuel fouling. The cylinder may be over fueled causing plug fouling. You may also have a bad coil or defective spark plug. Try swapping coil and plug with one from adjacent cylinder to see if misfire changes to that cylinder

Advance Auto will read your codes for free and give you a print out of codes. This will save you $100 and a lot of guess work. I know MAF, MAP and PCM sensors are common problems on these.

the engine (there are more than one engine)
has a distributor.
"have spark at coil down to dizzy but no spark at plugs"
this can mean only 2 things.
1: spark wires are dead. all 4, kinda hard to believe huh?
2: the dizzy is way off time. so time the dizzy and now spark
lands on each wire term.
if not a dizzy engine, post exact version of engine and country.

needs new turn up, like new spark plug, new plug wires, air filter, clean throttle body and intake mainfold. make sure all the small vaccum tube not black up and has vaccum present when pull out the hose.

Hi
Does the starter turn the engine when you try to start it or does it seem like the battery is flat again ? If the engine is turning over with the starter you should check to see if it has spark to the spark plugs . You can check this by taking the coil wire off the distributer end , inserting a spark plug into it and hold the side of the plug against any ground or metal part of the engine and get someone to crank the engine. You should see a bluish white spark at the end of the plug. If you have spark reinsert the plug wire . Now do a fuel pressure test. You need a test gauge for this. There is a test point { usually looks like a tire stem like on a bycicle with a cap on it} on the fuel rail. The test gauge will screw onto it and when you turn on the key you should get a reading os 35 to 45 lbs. Those are the first things to check if its not the battery or charging system.

go again to the dealer or at any gm service center with complete tools and computer diagnostics, by using tech2 find out all the code history, and freeze frame failure record. if no diagnostic code read, there are some program that delete or disabled that cant read by the diagnostic, hptuners will help you for that, read the vehicle data by hp tuners and reset it to original program, review all dtcs that cancelled specially to charging syatem, after reseting, diagnose it again and you can read the trouble codes to perform in rapair

Did you change spark plugs wires? fuel filter? I do not know if your car has MAF sensor, but if it does, clean it. Use CRC- Mass Air Flow Sensor cleaner. also check Spark Plugs Gap and coil (s)

Try changing the fuel filter and checking the fuel pressure at the shredder valve. The readings should be 60 to 65psi with the fuel line pressurized with the engine not running, once the engine is running. It should drop by 5psi. Start with the simple things first. Keep me posted, be glad to help.

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I would try checking the Fuel filter and if none put one on their.