I'm trying to get a 2004 Impala 3.4L back on the road. I started off with a P0301 code, a #1 cylinder misfire. I replaced all the sparkplugs and wires, and the #1 was very worn, so I figured I had it. But when I started up the car again, now I'm getting the random/multiple misfire code. I've checked my coils, ignition module, fuel pressure, and I sprayed all around the intake manifold and vacuum lines with carb cleaner, no change in the idle. There are three electrical connectors to the ignition module, I checked for battery power, it'* good. I checked the crankshaft position sensor, it'* good. There'* one other connector, it runs from the ignition module to the PCM. The motor runs the same if leave that connector disconnected, I found that out by accident. I've checked voltages to the EGR, and they're ok. I'm hoping someone will have some ideas, rather than just randomly throwing parts at it. Thanks for reading this whole thing.

Be nice if you had a scan tool that counted misfires, but if you don't, then did you do a coil output check?

Did you use OEM plugs?

If spark is ok on all coil terminals, then you have an injector problem, mechanical/compression problem, or could have a leak at the intake manifold, be it air or coolant....narrowing it down to a cylinder makes it easier to diagnose.....

How long has this vehicle been down for and for what reason?

It hasn't been driven much, it'* the wife'* other vehicle, it had a check engine light, which was the P0301 code, and the plug on that cylinder was very worn. The plugs that were in the car were the factory originals, and I had a hard time getting the ones on the front side out, in fact #4 cylinder broke off, and I had to tap it out, and put in an insert. I used Bosch plugs that were recommended for this vehicle. I had thought perhaps it was an injector issue, I'll check that next. Oh, and I checked the spark, it was good on all cylinders. If I have to do the injectors, I can check the intake manifold at the same time. Thanks for your reply.