: Changing Spark Plugs in 2004 SLS

06-03-12, 11:10 AM
It appears that spark plug configurations on Cadillacs change frequently. In a search for 2004 SLS, I realized that the 2003 configurations appear different as do the 2005s. So in order to contribute to the forum (you can deem the contribution useless or the result of my inability to conduct a search, but so be it).

Here are the steps I ran through in changing the spark plugs in my 2004 SLS with 85,000 miles. BTW, the plugs I removed were black, but the electrode looked good and the gap was still right on, so the change may have been premature.

1. Remove pretty Cadillac engine cover (Figure 1).
2. Unhook the "spark plug wires" at the harness (see figure 2).
3. Remove the four (2003 appear to have 8) bolts that hold the spark boot manifold or rail to the engine (see figure 2).
4. Remove spark boot manifold (I had to pull up on the radiator hose and cover quite a bit to wrangle this out, it was a very tight fit). (Figure 3)
5. Now for what out of my own inexperience turned out to be a very time consuming process...but does not have to be to remove and replace the spark plugs. Love it when repair manuals write this as if it is like opening and closing a door.

One problem is that in the tight quarters, the radiator hose and vanity cover do not give you a straight shot. Not a good design for removing and replacing spark plugs in an aluminum block as you have to either pull the hose up to get a straight shot or use a U-joint, which means that a process that really needs to be well aligned at the very end of the plug removal and starting the threads during installation are "unstable" and hard to control. None the less, I prevailed by using my fingers as a guide during these important steps.

The problem I encountered is that not only are the spark plugs recessed what appears to be about 20 feet deep in the engine (at leas 6" to the base see Figure 4). Be sure and blow the dirt out before removing the plug. To make matters worse, there is a small "lip" on the side of chamber, at about the top of the plug, that apparently keeps dust and dirt out (or in) around the spark plug boot. I was using a cheap 5/8 spark plug socket that was binding on this lip. So it made it difficult to tell if the socket was on the plug and made it feel like the plug was turning hard. This lip caused the spark plug socket to disconnect from the extension and required me to pull it out with a pair of needle nose pliers. I mean this was no easy task and took a lot of force to remove. When removing the plug, I could continue to rotate the socket and that seemed to help, but removing the socket after installing the new plug took two to three hard pulls and numerous slips. The application of WD-40 did not seem to help much. Now for the embarrassing part. On the fourth plug in the front, I had had enough and dug through my tool box and found my Craftsman 5/8 spark plug socket that on first glance did not look much different than the cheap one I was using. I decided to try it because I had nothing to lose and it slid right in and out of the recessed spark plug hole with ease. So the key is use a thin walled spark plug socket on these.
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Back Four Plugs!!!
Most posts on here talk of the horror of the back four plugs. Having once replaced the back plugs on a Ford Tempo, I understood their concern and went into this with the whole afternoon and next evening at my disposal if things went wrong. Having said all of that, it was a piece of cake.

1. Remove air pump/valve. I chose to remove the rigid line at the bottom rather than behind the pump/valve. It seemed that the risk of dropping the nuts during R&R was better than cussing two bolts I could not see nor had good access to. There is a wire and the rubber tube that need to be disconnected. I disconnected the rubber tube last after the three bolts that hold the bracket to the engine and the nut that holds the rubber tube bracket to the main bracket. You will need a u-joint to get the back/bottom bolt as it angles toward the fire wall.

2. Unhook "spark plug wires" and plastic cover. Easy as it sounds
3. Unbolt spark boot manifold. This is pretty easy as it is held on by two bolts and two modified bolts that serve as the posts to hold the cover on. These are fairly wide at the top and may not facilitate the use of a regular deep socket. I did not have a 10mm deep socket, so it took a while to unscrew them with an open end wrench.
4. Unclip some pesky wire near the rubber hose for the air pump/valve and you are ready to remove plugs.
5. Remove plug. If you have a thin walled socket (see above) and a 6" extension, this is a piece of cake. Took less than 20 minutes to remove and replace all four plugs. Easy access compared with the front four.

I had the back four plugs in and out and the car back on the road in less than 2 hours.

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06-03-12, 01:06 PM
Your ignition system is the crossover between the 2000-2003 Northstars and the 2005+ model. All Northstars are a DOHC design, so all spark plugs are deeply recessed in the cam cover/cylinder head wells in order to maintain the semi-hemi pent-roof combustion chamber design. There are ideas and cautions to observe when removing these spark plugs from an aluminum head. Look in Discussions, Item Specific: Cadillac Tech Tips or the GM/Helm service manual. Use ONLY the recommended AC Delco double platinum plugs. It is worthy of note that some spark plugs in a high mileage engine (>80,000 miles) may have oily shells and insulators. Normal: The O-rings in the cam cover well seal tend to weep over time.

For pictures and illustrations of the 2000 - 2003 ignition system and its parts look in my albums.

EDIT: Good to see that you elected to remove the two 10mm nuts securing the flex pipe flange to the right exhaust manifold: Some wrenchers try to bend the flex pipe and AIR valve out of the way....... and guess what always happens..............

Good pictures and good basic info for any 2000 and later Northstar sidewinder engine.

For clarity, here is the 2000 - 2003 ignition coil cassette and plug arrangement..........some "2004" engines, depending on build date and country of delivery, will have the 2000 ignition system. Check before you order parts. (Pictures now in my albums)

00 Deville
06-05-12, 05:36 PM
Nice write up...

I did the plugs on my 2004 Deville yesterday the setup was exactly the same as yours. I found the front bank very easy to do once the top radiator hose was moved out of the way by flipping it 180 degrees towards the rear of the car. I also found that the ball on the rear studs was too large to be able to use a 10mm deep wheel socket on them and ended up using a wrench to remove them also.

07-04-12, 04:55 PM
Thanks for the great guide, much appreciated. For Bonneville GXP owners, it'll be a little bit more tight because of the cowl hanging over the back of the motor.

10-19-12, 03:37 PM
Looking at the pics, I see that the coils are slightly different for the front or rear. When I did the plugs on my 05 Deville, it had the same arrangemant. Looks like either would function front or rear, but the color of the coils and length of the flexible part of the spark boots are different, although the total length looks the same. Anyone have an idea why?