P10304 Cylinder 4 misfire

My 2004 Trailblazer 4.2L, with 75,000 miles started idling rough (seems to run ok down the highway) and the SES light came on. I plugged it into a codereader and it is saying P10304 Cylinder 4 misfire. I replaced the plugs but it did not fix it. Would the coil pack be the next thing to check? I was thinking about switching around the coil pack on that cylinder and another and then plug it back in and see if it reads misfire on another cylinder then I would know. Anybody else had any coilpack problems to speak of?

Anybody else should be changed to almost everybody that has them will have problems sooner or later. :grinyes:

Yes you can switch them or remove it and put a spark test in the end of it to check for good hot blue spark.

And always use the good AC Delco spark plugs.

Good luck
MT

Ok. I swapped coils 2 and 4 around and its still showing cylinder 4 misfire so it wasn't the coils? Has there been any trouble much with injectors on these? What else should I look for?

Ok. I swapped coils 2 and 4 around and its still showing cylinder 4 misfire so it wasn't the coils? Has there been any trouble much with injectors on these? What else should I look for?

I would try a new or different spark plug and check compression on that cylinder and a couple of other cylinders.
Check for vacuum leaks on that cylinder.
And egrv valve leaking.

Is it a steady miss or one you can feel when driving.
Is fuel pressure and fuel trims good?
On some of them I have saw a wiring problem at injector plug in.
Remove plug in on injector and check for injector pluse and put it back on.

I don't notice the miss going down the road, mainly just at idle, and yes it is all the time at idle. You don't really notice it either right when you start it, but within 15 seconds or so you can tell. Oh, and another thing, if you leave it idling for a few minutes before taking off...the cruise won't work. If you start it up and then get up to speed fairly quickly without a lot of idling and set the cruise it will work.

I just put new plugs in it but I think I will try a different one in that hole, no harder than it is. I will also do a compression check.

I was looking at some documentation on the internet and it appears that it may be quite a pain to change injectors. By the looks of it you have to pull the intake.