96 Sunfire 2.2L Misfire after new Batt. & Alternaotr

[Epoxx]

1996 Pontiac Sunfire
2.2L 2200 OHV w/ DIS
190,000 Miles


Background
Vehicle had been shutting down on owner when engine speed got too low.
First the battery was replaced. Problem persisted.
Next the alternator was replaced. Problem went away.
Since the installation of the new alternator a new problem has come up.

Problem
Vehicle misfires. Hesitates on acceleration. Can totally die if it misfires too much at one time. But starts right back up.
Misfires increase in frequency as engine warms up under use.
Quick check with voltmeter of charging system = OK;
12v at battery terminals after sitting overnight
14v at battery terminals in idle, after cold start
13v at battery terminals in idle, after cold start with A/C & High Beams on
The death of the engine in these cases has been much different than how it would die before the alternator & battery were changed.
This death is pretty sudden after a rash of misfires. Whereas beforehand it was a gradual fail of systems due to lack of power.

Personal Take
Given that this happened so suddenly I'd want to say something happened during the battery or alternator installations.
That, or something decided to give out coincidentally.

I have searched the forum. Commonly seeing items pointing to the ignition system so like the plugs, wires and especially the coil pack(s). There is also a CEL. Given that it had been around for months now (don't ask me why they didn't get it checked, I forget what they said) I opted to not stop to have it checked at AutoZone at the time. Now that I look back on it, I should have had all the codes pulled (probabily new ones since the misfire started) and then had them CLEARED (Not even sure AZ will do that).

I am personally not very familiar with the common problems with GM systems (I am Honda) so I have come seeking recommendations as for what could be suspect/what to check on this vehicle. Also looking for any tests I can perform to help isolate the source of the problem.

Thanks in advance.

[J-Ri]

If the problem started immediately after installing the new alternator, then 99.9% of the time it is either something was damaged during the install (or it was already bad and a simple nudge pushed it over the edge), or the new part is bad. I'm assuming that since you listed it as a possibility, you checked for anything around the alternator that could have been broken or disconnected? It's been so long since I worked on a 2.2 OHV that I can't really think of what's over there, just check everything if you didn't already. The other possibility is that the alternator is leaking enough AC voltage that the PCM isn't getting a good DC signal back from anything as it should. The other .1% is that something just happened to fail at the exact time that the alternator was replaced. It happens. Diagnose it just like you would a Honda, they all work the same... suck, squeeze, bang, blow! When the battery was replaced, the body ground that connects to the battery tray may have been damaged. The tray corrodes from battery acid vapors condensing over it, and the ground can come loose. I knocked one off while replacing the fan once, had similar symptoms to yours, only adding that it was very hard to start. I cut the cable at the ground, installed a new end, and ran a new cable from bat- to the new ground on the upper radiator support where the two cables were joined. There probably won't be much left of the tray there if the batteries had been neglected for 10 years.