I have misfiring in cylinder #3 in my 2002 trailblazer. this only started happening after a recent tune up. i first changed the spark plug and it helped a bit. but not cured. then i changed the ignation coil and that didnt seem to help...should i change both together or seek a mechanic?.

could be plug or plugwires...have a tuneup maybe ??

cylinder #1 misfire, could be the spark plug, the cables or the coils, did you do a tune up to your car lately? or a fuel injector is failing, go for the plugs first and cables, some times is a process of elimination, Thanks

With a service engine light blinking...don't drive it.

When replacing the spark plugs, double check that the boots on the coils are installed correctly. Check these again, and make sure to either listen for or feel a little click which tells you it's properly seated on the top of the spark plug. This is a common thing, happens all the time to people with TB's and Envoys. I've even done this myself.

In case you didn't know, # 1 cylinder is up front near the fan, then it runs in order to #6 at the firewall. Possibility....(don't take this as doubting you), maybe the wrong coil was replaced and one or more coil boots weren't set properly? Some things to check anyway.

P0300 is the random misfire code. P0301 is the misfire code for Cylinder #1. When was your last tune up? non platinum spark plugs should be replaced around 30-60k along with the wires. With platinum plugs that extends out to 100k. I would try a tune up first plugs and wires. Reasonably cheap fix that is a prevenitive maintenace item anyways. If you have just recently had a tune up or it does not solve your problem you most likely have a bad coil pack on cylinder#1.

Hope This Helps.

Zeppelinx12

if you started out with no misfire at all and then got a misfire after the tune up that does seem strange, my best guess would be that the plugs are not gapped correctly or the spark plug wire is, not completely snapped on, or the wire on the 4th cylinder was damaged when it was removed, i would start out making sure all the wires are on, you will either hear of feel a small snap when the wire is seated on the plug good, also make sure the wire is connected to the coil good

Did you recently have your spark plugs changed? If so, putting the coil boots back on correctly can be a problem. When installing them, slowly push down until you hear/feel a snap. Another common problem is a bad coil, it happens, but lets hope not. There are 6 coils, 1 per cylinder and they cost around $75 each. Those are the 2 main problems that will trip that code for Trailblazers.

did you replace only one spark plug? that can cause issues because of differences in resistances between cylinders. also, did the map code stay off after replacing
?

Try the catalytic converter. I have the same problem and that's what i'm changing next.

misfire :-------- try checking your 02 sensors /fuel pump and filter.

for 51 cylinder misfire :---
Change the coil. Period. Very easy to remove from the vehicle if it's a 4 cyl. Follow that spark plug wire from the spark plug to the other end. What it's attached to you should replace
for 54 cylinder 5 misfire :---First you have to eliminate the most obvious problems, like spark plug and spark plug wire. If you replace those and you still have a misfire, then it's a good idea to look for a vacuum leak in the intake manifold

Since you have a misfire, the fuel in that cylinder isn't burning. Are you sure you have the firing order correct. Also try using one of your old plugs and wire for that cylinder and see if it works. If you only checked for spark at the wire, you might just have a faulty new plug- it happens.