P0302 then P0303

Compression and injector for those cylinder

What do you mean by replacing the coil pack? This only has to coils and 2 wires?

compression and injectors are good. moved coil over cyl. 3 to cyl 4 ond then moved wires from cyl 1 over to cyl 2. when i do this i get the misfire to move from cyl 3 over to cyl 2.

Inspect the coil more closely for cracks on the side. You may need to replace the other coil as well along with the wires. Also make sure you have Volvo spark plugs installed on here. Trust me on this. If you have some after market plugs especially bosch, you will be getting misfire codes. Also when do you notice the misfire? Is it more when cold, under load? Does the check engine light flash on you when you accelerate? Let us no.

this is the volvo that had the timing belt snap a few months ago. did a rebuild on the top half of the engine, valves, head gasket and so on. we needed to rewire the leads to the coil packs because some of the wires were exposed. we're thinking something with the rewire job. there was one wire that seemed to be coiled around another wire. i believe one led to the ground. that is the only thing that we were unsure of and did the best we could to duplicate the original wiring. thats all i can think of that would be causing the misfier problem. the car does its misfiring while at idle and low speeds{ under 25mph that i've noticed} when hooked up to the obd scanner the low end fuel trim varies between 3.6 and 4.8 don't know if that helps but there it is.oh, and keep in mind that i put new wires in and one coil, new spark plugs{got the ones the owners manuel listed}

Well to be on the safe side I would use Volvo plugs. As for the wiring harness on top of the cam cover, I have replaced maybe 2 of those for misfiring codes. The harness is under $100 from the dealer. Now has it been running rough ever since you put it back together or is this a new problem now?

i'm guessing the mis fire was an issue after we put the engine back together. i did take it into the shop because i could not fire it up. we had a pair of wires connected incorrectly and one banjo bolt not tightend down properly. after that the car started with its misfire problem. i may end up running it back to the shop to find the problem. i don't mind doing the work, just don't want to replace 18 things when i only needed to replace 2 things.

Did you have anything done to the head like a valve job or had it straighten if warped? Also did you mark all the tappets and put them back in there same place when you reassmbled the head? Your valves could be out of adjustment and for that you would need to remove the cam cover again and use a special tool to check the clearance. If they are too tight that could be your problem?

yes had the head sent into machine shop and had to replace 4 valves. the valves and caps were numbered for us to make sure each one was matched up. i'm pretty sure that the fellow that took care of the valves did a good job, he has had several years experence and has been with the same shop for about 11 years. i asked all kinds of ? before letting them do the job there. i'm just beside myself on this one and really don't know whet to do on the car next. guess i'm going to have to pony up the cash to get the shop to check it out for me.

Well if you had the valves replaced then there is a good chance you will need to adjust them by installing the correct size tappet. Like I mentioned earlier, you will need the special tool to do this procedure.

found out that the plugs are the cause of the mis fire. used champion plugs{same ones owners manual recomended}. also have oil leak and thought it was oil return line. not the case, turns out that the gasket sealant we used did not hold on the head gasket. going to dive into the engine again in a couple weeks to fix the oil leak problem. i'll keep you posted on the progress

The manuel never gives a specific brand they recommend? On any Volvo it is always better that you use Volvo plugs like I had mentioned earlier. Any other plugs will cause a misfire for sure like in your case? Well this has been a very long prject for you so I hope this thing is running good now for you.