I I suspect that a wire could be linked to an injector. l noticed on the wiring harness a wire is loose. I jammed it back in with some electrical grease but it's still misfiring. IHow can I properly seat the wire?

 

Again, the coil pack going bad is rare. But I had the Cat below threshold reading too from the Big, Very Expensive Scan tool. "The Maniac" is right. A clogged cat will cause back pressure that can reach all the way to your MAF sensor, if the car runs at all, causing a a miss read and the PMC trying to composite. And the same is true for a bad coil pack. Check your cat first. It's a more likely failure, if it passes check your coil packs. If you have a miss fire on cylinders 1 & 4, 2 & 5 or 3 & 6, That's a coil pack. It could be that one is going bad. Each coil pack fires for 2 cylinders. So if you have any miss fire of the above sets replacing all 3 is the way to go.

 

Maniac, I get it, by putting the car in gear, engine off, and rocking it, the engine will move/lean forward. Then looking the rear wheels holds the car, and therefore the engine, in that position. Nice trick! That's why I love this site, always something new to learn

 

If you're cat was clogged you'd be having drivability problems throughout the rpm range, not just at lower rpm. I think the P0420 is being set by the misfire as you suspect. The injector wires lock into place. If you found a loose one it may not be properly seated and causing the misfire. There's a (blue) lock on the connector that needs to be in the up position when you slide it onto the injector. After you slide it on hold it in position and push down on the lock to secure the connector in place.

 

At this point, I think we need to know what the exact code numbers are the car is throwing. This thread started with how to change the plugs and is snow balling into more with lots of speculation.

FYI - As for the coil packs, with that style coil, I have yet to find a situation requiring replacement of all 3 packs. And my limited experience with them failing, I don't trust the after market ones (I've had those fail and a used OEM work 100% fine). Just my thoughts. Coils are one of the last spots to check.

To help diagnose coils, the link below from the Bonneville guys may help:
http://www.pontiacbonnevilleclub.com...topic1683.html

 

Yeah i never suspected a coil pack. When i think of misfiring i think spark plugs. Theyre cheap enough that its worth replacing them even just to eliminate them as the problem. Im going to go ahead and replace all 6 and see how it runs. This car has 190k and god knows when they were last replaced.

 

Maniac, I know Since GM moved the coil packs off the engine, they are a lot less likely to fail. What I am saying is that all the symptoms are the same and if 1 coils is found to be bad, all 3 should be changed so that the impedance on all 3 is the same.
I do electronics for a living. The impedance of the old coils is not going to be the same as the new ones due to heat and use. Just like if you have a bad spark plug, you change all 6 so they deliver the same amount of spark to each cylinder, well the current to the plugs come from the coils. If one coil has let's say a higher impedance than the other 2, then 2 plugs are firing hotter.
At any rate, I'm Not here to debate, But that does come from more than 30 yrs of electronics and shade tree auto experience. The coils being his problem or not still need to be seen. And I absolutely agree with you that it is rare that they go bad. Just offering a direction to go if all else fails. And with his symptoms even though low on the list of things to check, they do make the list! Good luck again!

 

Sorry, if I sound like I'm making it an argument or debate, I don't mean to. I understand what you are mentioning about the impedance and I won't dispute that a new coil vs old one will vary due to any number of factors related to age.
IMO, these cars are not tight enough in performance and/or tuning that one coil's impedance being a little off from another one will make or break a difference (I've replaced singular coils about 3 times total I think and no codes, no performance problems that I'm aware of). Average coil cost is $20-$30 per coil. For some, that cost times 3 is a lot on a tight budget, for others no big deal.

Best way to put it, I'm not trying to say your advice about the coils is better or worse then mine. It's different but has a logical reason for it. Since my experience with these coils has always been successful with swapping just the faulty one, I base my advice off that experience. Hopefully that makes sense

 

No Hard feelings, I been going through it with my car being down for a week and the wife's Lexus having a misbehaving vacuum hose. I know you have more experience with the Monte than I, and that one day I will need to pick your brain to solve something. Keep on doing what you do, you can help a lot of people. And don't pay attention to the Old Man behind the curtain with the YelloJAC Monte. He's a little Off sometimes!

 

lol! No worries man, it's all good. We have all had different experiences and different comfort levels. I know sometimes I spent money on "overkill" for a fix to a problem only to make myself feel better. By the same, I've had my share of bit in the butt by trying to save a couple of dollars.

I'm just hoping the OP of this thread is getting some help from our back and forth