I have a 2004 Trailblazer EXT 4.2 S6 that started misfiring about a week ago and I've replaced all 6 plugs and the coil but its still throwing a code for cylinder #3 misfire. Checked the compression out and it was fine but when I checked for voltage on the wires that connects to the coils, cylinder #3 only receives 12 volts while the other 5 are receiving 14 volts. How can I solve this problem so it will fire properly and I can get my horsepower back?

i think its the ecu, i had misfire codes come up in my 06 explorer, changed everything like you did, it was the ecu, i got one on ebay with keys for 150, it worked, also ford systems require a fully charged battery

Timing could have jumped. Could be a bad head gasket also. even possible to be a small hole in piston check the cylinder for compression. Check the fuel injector to that cylinder if you have bad air to gas mixture it will throw a code of misfire change fuel filter check fuel injector to see if clogged. most likely it is the fuel injector .

Here's a link to your code.

DO NOT go back to this ripoff artist, he either doesn't know what he doing or is taking you for a ride.
Misfires are usually caused by bad spark plugs or coil packs. Find another mechanic.

The code you got may not have indicated the correct coil, that was bad

I would put the old coil back in #6 & either walk the new coil to another cylinder, or get professonal help in the form of a scan tool in Mode $06,
if applicable on your vehicle & check for misfires that why

Forget the PO300

if its a multiple missfire then i would suspect your fuel pressure is dropping or your regulator has failed and is sucking too much fuel causing the computer to overcompensate, these engines are also known for intake leaks

Number one is closest to bumper then just count back they go in order 1-2-3-4-5-6 then the firing order is 1-5-3-6-2-4 also if your having a misfire check for lose wire and if I remember right those had a problem with water contaminating the coil packs check for white on the coil and on the boot inside and out, if they are chalky you need to replace the contaminated parts and the seal to keep water out at the back of motor where hood closes.

Hi, my first recommendation would be to take the plugs out and visually inspect each one and check to make sure they are properly gapped, if they look fouled at all i would replace them without hesitation. try throwing a set of NGK plugs in the car to fix the misfires. other than that you may want to look at the wires. good luck joe

ignition coil is the problem.

The concern is likely caused by the coil which sits on top of the spark plug. Your P0301 indicated misfire on cylinder 1. Your P0316 indicated it occurs on the first 1000 revolutions. Your P0171 indicated lean on bank one. Bank one includes cylinders 1,2,3 and 4. Your lean code is strange but could be related to misfire. I would recommend swap the coil on number one with number two. Clear the code and drive it. I would expect to see a P0302 which indicates the misfire traveled with bad coil. good luck.