You have to remove the upper Cadillac intake manifold to replace the spark plugs and coil packs. Most people don't realize this until they roll past the 100,000 mile mark and start setting engine misfire trouble codes.
The General recommends replacement of original equipment plugs at 97,000 miles or earlier depending on the year and engine size. Although we'll discuss individual problems with aging Cadillac models here, there's a more important point in this article.
General Motors installed paper gaskets on the upper intake Plenum. In their defense, they probably didn’t think it would require removal so often. After 10 years or 100,000 miles these paper gaskets chips off like pieces of glass.
If you replace the original equipment Cadillac intake manifold gasket with an ACDelco or aftermarket metal and silicone upgrade, you'll be able to reuse them in the future.
Reusing the gasket is fantastic and let me tell you why. On some Cadillac cars, I've removed the plenum upper intake four or five times during the vehicles life span. In fact, I have a customer with a CTS pushing 225k miles. I wish I could Velcro that thing on.
There is a lot of good stuff hiding underneath of the overly wide upper intake. This leads to many reasons for removing it. Whether it’s for regular maintenance or diagnosis of more complex car problems this puppy has to come off.
As long as you properly assemble and torque the bolts correctly, you can reuse the upgraded metal Cadillac intake manifold gaskets several times. This is why I say properly assembly and torque.
If you install these metal gaskets and decide to crank down on the Plenum bolts, without a torque wrench you might distort and destroy the silicone bead seals. For this reason it becomes extremely important to use an inch pound torque wrench to achieve the proper tightness. The torque on the Cadillac intake manifold bolts comes in at 17 ft. lbs or 204 inch pounds. Now let’s talk about why this thing has to come off.
It's no secret that the GM V6 finds its way into many different General Motors automobiles. Whether it's a Cadillac, Chevrolet or Buick, misfire codes remains a common issue. Unfortunately, it's an issue requiring some diagnosis.
It's not always the coil and it's not always the spark plugs. Thankfully, these cars are pretty good at setting individual trouble codes for misfires on particular cylinders. In the case of a single misfire this gives you a fighting chance of finding which hole is causing the problem.
With that said, if you have a failure on more than one cylinder you might set the dreaded P0300 random misfire code. This puts us at a disadvantage, because the only information we can gather from this code remains the misfire is on more than one cylinder.
You can remove the General Motors coil assembly and use an ohmmeter on the individual coil packs, but this doesn't always point to a failed part. Unfortunately, sometimes these coils become intermittent and will pass a standard continuity check using an automotive meter.
About five years ago, my approach to the General Motors ignition coil problem was to replace only coils that failed. However, my recommendation to customers changed. I push for a whole set of new ignition coils. This way they won't have to return over and over again to get the defective coils replaced.
This also means I won't have to remove the plenum six different times. With that said, I use the metal Cadillac intake manifold gasket kit the very first time I remove the upper intake manifold. This way, when the inevitable happens and it needs to come off a few more times, we can reuse these parts.
Some say that Cadillac spark plugs don't last long enough. In my opinion it's exactly the opposite. They last too long. If you look up the maintenance interval for the 2008 Cadillac CTS you'll find spark plug replacement recommended at 100,000 miles.
On the Cadillac V6 of this year, they used steel spark plugs threading into aluminum cylinder head threads. When you add the length of time and miles these original equipment parts remained installed, removal can become a game of Russian roulette.
In most cases the plugs break loose and thread out on a cold engine. However, in some cases, they put up a massive fight and can ultimately damage the delicate threads of the aluminum cylinder heads. There are a couple of things that you can do to turn the odds in your favor in this situation.
First thing you need to do is only perform the operation on an ice cold engine. The colder the motor is, the better. It couldn't hurt to soak all the spark plugs down in a liquid wrench type product for an hour or so.
Note that you want to go back and continue to wet the area and not allow the miracle fluid to dry. Some mechanics swear by the trick of slightly tightening the spark plug before attempting to back it off. I've tried this method and it does seem to work in some situations.
Another thing that we can count on is using a thread chaser on the aluminum threads to repair slight damage caused by the spark plug removal. Although it's rare, I have seen thread damage that required the use of a Helicoil repair kit.
Short explanation of this repair is the complete replacement of the spark plug threads in the existing cylinder head. This is a delicate operation performed by professionals. Failure to install the Helicoil correctly or allowing metal chips down into the cylinder could force this auto repair to snowball into a cylinder head replacement.
There is one thing for sure. Replacing the spark plugs on a 10-year-old General Motors V-6 engine is like a box of chocolates. You never know what you're gonna get. The job can go smoothly and leave you with a big smile on your face. It can also put you on your knees crying in the driveway. Of course, I hope your experience ends with a smile.
We filed this Cadillac intake manifold gasket article on the tune-up and maintenance page. We did this because removing the intake is a necessary evil when replacing spark plugs on a Cadillac V-6. Visit the homepage to find out what other types of information we cover here.