New coils in the Caddy

[G-MAN]

I posted here about the 2008 Cadillac STS I got a couple months ago. I also commented on how the 3.6 Pentastar in the Chrysler 300 I used to have was smoother at idle.

One of the first things I did after getting the Caddy was replace the plugs. After getting an oil analysis done by Terry Dyson, he recommended that I also replace the coils, which I did today. The old ones were the OEM Bosch coils from the factory. After installing six new Delphi coils I can report that this engine now idles just as smoothly as the Pentastar.

For those with over 75,000 miles on your OEM coils, replacing them is probably a good idea to optimize combustion dynamics, with some tactile results as well.

 

[Chris Meutsch]

Good to hear, but don't you think the real fix is that you changed brands and not the age/mileage?
I've put more than 450k on OEM Honda coils and never replaced them in my ownership. Never had any idle issues that changed between new and 220k miles/10 years.

 

[440Magnum]

I've never replaced a coil that hadn't failed completely, or visibly arced over at a terminal. Now boots and contacts, that's another matter. I assume its a coil-on-plug system, are the boots not separately replaceable? That might have been the only thing necessary if so.

On a related note, I changed the plugs in my 392 yesterday at 35k miles. The manual wasn't clear about factory plug type- the 5.7 engine has copper/ 30k mile plugs, but there's NO plug change interval indicated for the 392 (not even listed at 100k miles- odd). It had NGK iridium plugs from the factory and would have been good to go far longer, as it turns out, but they're so easy to replace that I don't feel too bad about it. I put in a set of Autolite Iridium plugs, and refreshed the dielectric grease on the boots so they don't stick to the plugs. Absolutely NO change in idle or other characteristics, and that's what I'd expect. The coil packs on that engine have twin boots (one per plug, 2 plugs per cylinder, 1 coil pack per cylinder). The boots look pretty easily replaceable when the time comes.

 

[WobblyElvis]

My son's 2008 cts had a misfire under load. Mechanic recommended changing a few coils and the plugs. Changed just the plugs and ever is fine. 110,000 miles on it.

 

[G-MAN]

Originally Posted By: 440Magnum
I've never replaced a coil that hadn't failed completely, or visibly arced over at a terminal. Now boots and contacts, that's another matter. I assume its a coil-on-plug system, are the boots not separately replaceable? That might have been the only thing necessary if so.


It is coil on plug and the boots appeared to be part of the entire assembly, i.e., not removable or replaceable.

 

[cptbarkey]

you might have saved a ton of money by analyzing it with a misfire pid but at least you are happy.

 

[G-MAN]

Originally Posted By: Chris Meutsch
Good to hear, but don't you think the real fix is that you changed brands and not the age/mileage?
I've put more than 450k on OEM Honda coils and never replaced them in my ownership. Never had any idle issues that changed between new and 220k miles/10 years.


I did not replace the coils to fix an idle issue. That was just a serendipitous result. The coils were replaced because oil analysis showed weak spark and less than optimal combustion dynamics.

I did the same thing with my Audi A4. I replaced the standard coils with the "Red Top" coils for the V10 in the R8. These coils are documented to produce a much hotter spark than the "Black Top" coils and it really showed in the oil analysis results. However, in the Audi, there was no noticeable difference in idle (but the OEM coils only had 26,000 miles on them).

 

[RoadRaceJosh]

My 1997 BMW had a misfire only under load. I changed the well worn plugs and found no improvement. No check engine light. Hooked up to the OBD port and found the CEL should have been on. Also found a misfire code for cylinder #3. I swapped coils between #3 and #5, got a misfire from #5. Swapped the old #3 coil for a used one from a BMW V8 that was being parted out and went on my merry way for $30. That $30 bought me 2 used coils so I now have a spare. The only lesson here is to change the plugs before they are so worn that the coil insulation breaks down.