'03 Impala misfire problem

[ogre73]

OK. I have a problem I am trying to figure out on my own, since I have already dropped $100.00 on diagnostics that only partially help and I don't want to drop three times that before getting the problem actually fixed. Here is the concern:

About a month ago I took the car to the dealer because of a rough idle. It's wasn't throwing any codes, but they took a snapshot. The diagnosis was that cylinder 3 had a slight misfire. They swapped plugs 3 and 6 and the misfire still stayed on 3.
I asked about the wire, they said not the problem. They thought it was the fuel injectors being dirty, and suggested I try Techron.

The car has 57K miles on it. At around 40K I replaced all 6 plugs with platinum, replaced pcv valve, air filter, and I change the oil regularly. I had the garage down the street replace the fuel filter and change the oil before I added the Techron. I added two bottles after the fuel filter replacement and drove it for a while. It got no better, and continued to get worse.

I took it to the garage down the street two days ago because it is getting to the point where I don't know how much longer it will go without quitting on me completely. They said that by misting some water on the plug wires up around the coils they could get the Check Engine light to come on, and diagnosed "(can't remember the exact term here, but something like multiple) misfiring cylinders". Great. I already knew that. So the garage said I needed a tune up to replace the plug wires.

I replaced the plug wires the same day. No change.

So that brings me to a couple of things:
The fuel injector.
The ignition module.

Before I go and blow a ton of money on an ignition module or coils, or go spend too much to have the fuel injectors cleaned,:

CAN ANYONE THINK OF ANYTHING ELSE that I may be forgetting/overlooking?
Thanks.
Jim

[ATOZBODY]

I Had a poor run and stalling condition. I repaced to fuel pressure regulator (dealer friend told me they replace them commonly for this). Runs great. Its on the top of the engine in the front. 30 minutes to replace.

[ogre73]

After I replaced the plug wires the problem was still there. I misted some water on the wires in a dark garage, and could see a LOT of arcing going on around the coils and even halfway down the wires in a couple of places. My mechanic told me that I should have used AC Delco wires, so I will save up for those ($55.00-jeez!). In the meantime, we had a very dry couple of days and during that time the car ran much better, although not perfectly. So this all leads me to beleive the spark plug wires.

At about 36000 miles (20K ago) I replaced the plugs with Bosch platinum. Could these plugs be sending too much voltage through the wires, breaking the originals down, and being too much for these cheap Autozone wires from the start? Or could there be something else in the electrical system that allows too much voltage? Because something caused the original wires to degrade and is too much even for new cheap wires.

Any thoughts on that would be welcome.

[ogre73]

Update:
I had an accident in early February, so was more concerned about that for the last month than how the car ran.

Yesterday I finally decided enough was enough and I was going to figure out this misfire problem before I caused damage to my engine.

I went down to the local (reputable) parts store and shelled out $101.00 for six AC Delco (NGK) plugs and a set of AC Delco wires. I figured if this didn't fix the problem at least I would know that it WASN'T the plugs or wires. So I put them on.

Following the switch I took a test drive. The car first of all started much easier than before. Then, during the drive, I went up a little hill at about 30 MPH. This type of driving had always caused the misfire to be so pronounced that it was scary. So as I anticipated this and it didn't happen I felt really wierd, but happy! I figured, good, but the real test will be driving the 65 miles to work tomorrow.

This morning I drove the combination of highway and city driving 65 miles to work and not one problem.

From this I have to deduct: The plugs were the original culprit, as they were installed with factory wires. Whether it was too much voltage or something else, they broke down the wires. Replacing them with cheap Autozone wires made things much worse.

I will always use AC Delco parts for these critical components in the future!

Problem solved.