1998 Cadillac Deville-change out plugs and wires

Need to change out plugs and wires in my cousin’s Caddy when she arrives. Not being familiar with this vehicle, I’m worried it could be a bigger job then I’m willing to take on. So, I’m wondering if anyone can shed light on whether or not I need to roll the engine forward to access the 4 rear plugs, or just how difficult this job could turn out to be. Her mechanic gave her an estimate of $370 total.

According to this guy it’s pretty straightforward, but I can’t vouch for the correctness of his answer:

Thanks “jesmed” for the link. It sure doesn’t look all that difficult. I’m trying to justify the $370 estimate for doing this. The car hesitates, or runs rough, while accelerating then smooths out when at speed. The plugs and wires are thought to be the originals and may be the cause for this problem.

Repairpal.com gives an estimate range of $280-$370 just for changing the plugs ( based on labor rates in my area). So the $370 estimate your cousin got for the plugs and wires is not unrealistic.

A NorthStar tune-up can be somewhat of a challenge…

Especially if the plugs have truely been in there since 1998.
Honestly, you might want to simply explain that you’re uncomfortable with doing the job, afraid you migh damage something, and bow out of the job. Or point out that if the plugs won’t come out you won’t force them so she may have to bring it to a shop after all.

Thanks guys for all the info. I’ll take a look under the hood when the car gets here, but I’m now nearly convinced to take it to a very reliable local shop base on all your input.

If at all possible, find a mechanic who specializes with caddys. I found one, and he’s without a doubt as good as they get ! You really can’t compare prices for repairs to other vehicles, because a caddy is going to be more complicated depending on the repair. The newer ones, not so much, but if it’s 10 yrs old or more, it really takes a talented mechanic with knowledge of a caddy.

Thanks “Free Wheelin”, we decided to take the car to a reliable local mechanic who has work on my vehicles and I have full confidence in him. I am relieved that we are sending it out rather then trying to do it myself. Car Talk and you guys kept me from biting off a bigger job then I imagined prior to these conversations.

If its a Northstar engine, you can gain rear access by unbolting the coil pack and moving it out of the way (don’t disconnect anything I think except the main plug for the ignition module and just unbolt the module with the coils intact-its been a while). Also try it cold first and gently see if the plugs unscrew or not.

Thanks Bing, it is a Northstar engine and I’ve been hearing more and more about how difficult these engines are to work on. I’m anxious to see how my local mechanic does when he gets started on this project, (which I didn’t think would be any big deal).

Ah yeah. Well, plugs aren’t that bad if you have small hands. The water pump requires a special tool. I finally took it to the dealer. There is a small serpentine belt for the water pump that you should make sure is OK. They are cheap and easy to replace but will cause instant over-heating if they break. The radiator comes out the bottom so need a lift. The starter is under the intake manifold and cleaning the EGR tubes requires taking the transmission out. The EGR itself is $500. I needed the factory manual to figure out changing the serpentine belt and if you ever get a head gasket problem just forget it. All in all though its been a pretty good engine but has a tendency to eat coils and spark plug wires. I’ve got the Olds version without the computer speed limiter so I think it’ll do about 130. Never had it past 90 though. Still it gets 25-28 mpg on the highway but we only put a couple hundred miles a year on it anymore. Have fun.

The Caddy is now in the hands of my mechanic so we’ll see how this turns out by tomorrow, I would think. I just hope those coils are alright, although I would think they are easy enough to replace…not sure what they cost!

If I remember right the coils are about $80 each and the full wire set another $60-80. If you start to get a slight miss at idle, suspect the coil and/or wire.

Turns out the Caddy had one cracked plug, the mechanic thinks the plugs are originals. He knows the wires were the originals. Replaced plugs and wires…car runs smooth now. I’ll be sure to tell my cousin (her car) to listen for a slight miss at idle. Thanks for all your help.


By cracked plug, do you mean that the ceramic cracked and you were able to remove normally?

Or the plug broke off and you had to extract it?

In any case, congratulations!

I suppose this goes to show that sometimes maintenance IS the repair