I have replaced my Plugs, Wires, And Coils twice I have even cycled new injectors. None of the plugs were fouled either time. Here is the kicker, sometimes it runs smoother then others but never 100% smooth at idle .

I've even change my fuel filter. Check engine light has been on about a month now.

Can a dying battery be it ? or a table error?

Can the harness that leads to the coils be replace independently?

 

Constantly getting just cyl 5 even after swapping stuff around?

Try the injector. Lack of proper fueling can cause the misfire.

 

Yep and I have .
I did the fuel filter, no change . My mechanics free blind advice was the change the harness that leads to the coils. Is that a independent harness? or could it be something silly and cheap only grizzled vets know about. Like the battery which is pretty old and should be bad but not giving any indications of being bad.

 

I believe it's all one harness.

 

Low voltage to an injector can alter its duration which would impact the amount of fuel being introduced. A battery in good condition and a full charge is important. Have your battery checked and if it shows signs of a bad plate and/or won't retain a full charge replace it. Before replacing the wiring harness test the resistance. Since it is only one cylinder it may be a loose/dirty connection or a frayed wire. Here's a how-to describing the resistance test:

Part 1 -Fuel Injector Test (GM 3.8L).

 

Bad coil will cause misfire on 2 cylinders. Were they new injectors or used? I would start by ohming out all the injectors and flow testing them.

 

Actually, most times a bad coil will cause 2 cylinders to misfire, but it is possible to have a problem with one tower/post on a coil to cause one cylinder to have a problem. But in this case, the OP said all coils have been changed and the result stays the same.

I would not suspect the ICM, as it would cause 1 coil to have a problem, thus 2 cylinders misfire. At this point, you are up against a wall, it may not hurt to remove the ICM, take it to a parts store and have them test it. I expect it to pass.

Before going crazy, I'd do a simple vac leak check. Use a can of starting fluid, mist around all vac connections. In this case, I'd pay special attention to the #5 injector and where the LIM gasket meets in that region (this is checking for a bad seal around the injector in the #5 spot or a problem with the LIM gasket sucking in air around the #5 position). If you have a vac leak, once you mist starting fluid around that spot, the car will suck in the fluid and the idle will change.

Another random though, I am not sure which position #5 is in the firing order, but it might be worth checking the fuel pressure. Ensure the pump is not beginning to take a crap or the fuel pressure regulator is not failing.

Personally, I have never heard of a dieing battery causing a mis-fire. Once the car is started, even with all the computer controls, the alternator should be able to sustain power. Heck, I just changed a battery that since I owned my Monte, if it sat for a week, I had to jump it (since I park the Monte during the winter, the battery lasted longer then it should have). It now got to about 3 days and it needed jumped. Parts store did a free battery test and that was it.

 

I have a cylinder 1 misfire code that's been on for a while now. Changed coil pack, wires, plugs, and even the injector. Running a compression test tomorrow. We'll see how that goes providing that I can get the f***ing plugs out and run the test before the engine cools down. Low compression is the next possibility after the injector, which could tell you a bunch of things about how the cylinder performs mechanically from a blown head gasket to worn rings, etc.

 

It goes like this:

coils | (2) (4) (6)
6/3 |
5/2 | --ENGINE--
4/1 |
.... | (1) (3) (5)

 

3 coil packs later. BWD pack from pepboys , first 2 were duds. I don't know if thats a brand problem or a bad shipment. My previous packs where from jegs