Take a standard automotive 12V bulb that has wires on the bottom that you can straighten out, and use it to see if the #3 injector is getting a signal to fire. You switched the injectors, so the problem is not the injector itself, but you need to confirm the signal. When you know the engine is misfiring, shut it down, pull the electrical connector off the injector, and touch the two wires to the contacts in the connector. Crank the engine and observe the light. If it doesn't flash, or flashes irregularly you have a problem. If you are not sure what a normal flash frequency would be, try it on a good cylinder first for a reference.

You are taking all the right steps to track this down, so now its time to start digging a little deeper.

Did this and the flight flashes at a steady pace. Now since he'* switched the injector from 1 to 3, when the engine is off, moving the fuel rail, a slight fuel leak appears. When engine is running it doesn't appear to leak. Will pick up some o-rings today and change them.

Any other suggestions?

Are you still having a misfire?

Yes Dan - he'* going to change the "O" ring on the injector in cyclinder 3 and pick up some carbon cleaner. Not sure what else to try.

UPDATE: Dh went to replace the "O" ring(*) and on injector 1, 3 & 5 = one had cracked ceramic and the other two injector'* ceramic were missing. He didn't think this could be the cause of the misfire code P0303 - could it? He'll pick up three injectors tomorrow and replace them. I'm crossing my fingers. Poor guy is about done with this code!!!

No, that wont cause a misfire. The injector is not in the cylinder, it'* in the intake. Here'* your check list.

Spark plug
plug wire
coil
ICM
injector
injector plug
valve spring
damaged valve
damaged piston, chipped

{Insert spouse haking his head}

These items in red have been completed:

Spark plug
plug wire
coil
ICM
injector
injector plugvalve spring


He'll be checking these three items with a "compression tester" tomorrow or Monday?

damaged valve
damaged piston, chipped
damaged piston, chipped

When he takes the belt off the super charger, the rattle noise goes away. So, he'* ordered the supercharger coupler to hopefully take care of this problem. So, we'll wait and see on the compression test. Crossing our fingers....

Thanks

Not sure what happened above - here are the last three items for the compression test:

valve spring
damaged valve
damaged piston, chipped

A bad valve spring will not show up with a compression test, and neither will a chipped piston.

Ok, dh finally made it back home from being held over at work.

The COUPLER worked! YEA!!! One down and one to go.

We still have the misfire P0303

spark plug
plug wire
coil
injector
injector plug
valve spring
damaged valve
damaged piston, chipped
damaged piston, chipped

I was mistaken before. The ICM is the only item not done above. Is there a way to test the ICM? Can they be removed and taken somewhere to be tested? If not, we'll probably try a wrecking yard prior to new purchase. If we have to go this route, does anyone know what years of Buick Regal Supercharge GS'* interchange with our 1998 with regards to the ICM, or another Buick product?

Here'* the symptoms: There'* a misfire at idle. While driving you don't feel or hear a misfire. It does flutter when you throttle up.

Thanks everybody!