: 50 Deville - Code = P0300 current

08-07-08, 10:07 AM
I have a 05 Deville and it had an intermittent miss that is now constant. Code only gives me "misfire".

Miles = 85,000

I have listened to all the injectors fire and the front coil packs individually with a stethoscope. The front coils have a strong spark sound as they fire, the rears sound very weak.

It looks like the rear coil pack has crapped the bed. If that is an incorrect assumption, please advise.

Any tips on how to get to this piece. I don't really like doing things the hard way.

Any other troubleshooting advice would be appreciated.

Thanks in advance.


08-07-08, 11:24 AM
i had the same thing on my '01 DTS. my front coil was bad. i bought mine on ebay for $20, its used but works fine. the front (gray) & back (black) are interchangable so if you do find a deal on one it will work for either side. the back wasnt too hard to change. hardest part was getting off the unit that sits above the back coil. its a tight fit but isnt too bad.

08-07-08, 11:34 AM
Thanks for the info. I searched for two days to find the part. ONLY availability was local caddy house ($354) or Rockauto ($236 shipped overnight). Rockauto had one left.

I even did a search of salvage yards and came up empty.

Not excited about swapping this part out on a car with 85k miles. If it was 1970, I could understand a coil giving up the ghost.


08-07-08, 06:07 PM
85K miles? That won't be the only thing failing in the near future.

08-07-08, 07:15 PM
85K miles? That won't be the only thing failing in the near future.

Care to throw me a bone here?

08-08-08, 01:17 PM
Well this is about the least fun I've had recently. I have managed to get the valve over the rear cam cover off and the plastic cover off the coil pack assy. At least I can see it now. I'll try and take some pix and a list of hand tools needed for this when I'm done.

Anyone that wants to chime in with their experience on this would be helpful.

08-08-08, 01:36 PM
Look here. Ask him to e-mail you the instructions (with nice photos)


08-08-08, 01:43 PM
Hopefully he will stop buy. As a newly registered user, I don't have PM privleges yet. :(

If anyone would be kind enough to forward them to me I'd appreciate it.

mrodeniii at gmail dot com

Thanks in advance


08-08-08, 07:24 PM
OK last post on this problem. I got the coil swapped. It was indeed bad. Thought to myself.... plugs? Nah, this has factory platinums in it.

Bad bad bad decision. Put it all back together and it is better but you can tell one hole is missing pretty regularly. Not happy now. I pull injector leads and isolate the bad hole. Second from the right as you look to the rear.

So I pull it back down - hot. That is a real treat :)

Let it cool down and snatch the plug out. Carbon fouled - badly. I'm amazed it ran as well as it did up until it just dead shorted. The others are pretty bad but not dead.

So off to scrotumzone for a new set of factory plugs. Whip those babies in and it is now purring like a caddy should.

Live and learn I guess. Oh, for you GM engineers that thought mounting a DOHC V8 transversly was a smart packaging idea... here is a high hard one.

08-08-08, 07:42 PM
You might want to clean the throttle body and give it a few wot runs.