Rust on ignition coil terminals - replace?

[StevePT]

While replacing the spark plugs on my mom's 99 Regal GS 3.8L SC, the 2-5 coil had what appears to be arc rust on both the terminals. I checked the resistance on all the wires and everything checks out at about 1000 ohms per foot, except the 2 and 5 wires are about 90K ohms each.

The car has been running decent, but this is obviously a problem. Is replacement of the ignition coil necessary? Any ideas on what is the cause of this rusting of the terminals?

Thanks!

[StevePT]

Now the plot thickens I checked the resistance on each of the coil packs and they all came out around 5.2 ohms.

I cleaned the terminals on the ICM and checked the resistance between the two blades for each coil. I didn't get any resistance on the top and bottom to pair of blades, but on the middle two, which the coil pack for 2-5 sits on I got about 1.2m ohms.

Are these things usually a go-no go type of ignition part or could I possibly have some resistance in the wires leading to the ICM or in the ICM itself which is causing the 2-5 coil to arc on the wire connector pins?

[BNaylor]

How old are the plug wires? 90K ohms is way too much for #2 and #5. GM specifies no more than 30K ohms on the longest wire which should be to cylinder #6.

In comparison on my '01 Regal GS, the AC Delco Premium Silicone 7mm wire for my cylinder #2 shows 4.65K ohms.

Don't remember off the top of my head but I'd have to check the service manual and see what the coil resistance specs are.

[StevePT]

The plug wires are the standard AC Delco wires so I would assume they're the originals that came on the car in 99. The car has about 60K miles on it.

Like I said, all of the wires had low resistance, (1-3K ohms) per wire except the two wires that were connected to the coil pack which had rust on the terminals measured out at around 90K ohms.

This evidently isn't a very common problem because I did a search on the words "rust coil terminals" and only came up with one thread where a guy had the same issue.

[BNaylor]

Originally Posted by StevePT

The plug wires are the standard AC Delco wires so I would assume they're the originals that came on the car in 99. The car has about 60K miles on it.

Like I said, all of the wires had low resistance, (1-3K ohms) per wire except the two wires that were connected to the coil pack which had rust on the terminals measured out at around 90K ohms.

This evidently isn't a very common problem because I did a search on the words "rust coil terminals" and only came up with one thread where a guy had the same issue.

I don't believe rust on the coil terminals is common but it probably depends on where you live. I don't have any on my 3 "W" bodies but I'm in the desert Southwest.

I have heard of moisture contamination under the coil packs causing ignition control module (ICM) problems. Arcing may be visible.

[StevePT]

Well I ordered some new AC wires and a new coil. The car needs to be used inbetween now and when the stuff arrives, so I put it all back together with new AC iridium plugs on all the cylinders except 2-5 (I used the original NGK platinums).

First thing I noticed is that the 2 and 5 boots going onto the coil pack were extremely loose. I didn't feel any positive retention when putting the caps back on so either it just so happened to be those boots were built a bit loose, the terminals on the coil were under the acceptable diameter tolerance or the coil is weird and was arcing on the clip in the boot and everything got spaced out over 60K miles of driving.

Anyway, I squeezed the clip in the boot together a bit, put it back together, drove it and everything drives fine.

I know it drives fine now but I think I would have got to a point eventually where it would have been arcing completely at the coil terminal and never sent any voltage to the plug and then started running really bad. Glad I caught it now and it's not going to hurt to have new wires and replace that coil...


BTW- I'm in the Pacific NW and it's wet here 9 months out of the year. But then again on my 97 GP when I did spark plugs about 10K miles ago there wasn't any sign of this rust so I think it's independent of climate.

[BNaylor]

Nothing like good preventive maintenance.

The loose fit is common after the wires have been removed off the coils a few times. The new wires will take care of that.

BTW - The new replacement AC Delco Premium Silicone 7mm plug wires will not have any cylinder markings on them so exercise caution during installation. Good luck!

[StevePT]

I'm pretty sure I know which spark plug wire goes where.

I think it has something to do with the coil though and in the process of arcing onto the terminal in the boot it wore off the coating on both surfaces and the terminal lost its sprung form. It seems too coincidental that both the wires on just that one coil were rusty like that.

I know some guys that think on older engines with distributors the wires go from No. 1 cylinder and then clockwise around 2-3-4-5-6-7-8 and they couldn't understand why it ran worse after they changed the plugs and the wires...