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'98 SLS "tune-up"

Started by Greg McDonnell, January 15, 2008, 08:36:27 AM

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Greg McDonnell

I would appreciate advice regarding what, if anything, I should do regarding a "tune-up" for my SLS.  It will be 10 years old next month and I am sure it still has the original plugs/wires etc.  When I bought the car in '02, it had 29,9xx on the odometer.  I was advised at that time not to change the plugs as they are designed to last for 100,000 miles (so said the parts guy at the Cadillac dealership).  Well, in 10 years, the car has only 40K on its odometer.  It sits a lot as I don't need it fr daily transportation.  I do, however, want to maintain it properly.  It looks and runs fine but I did notice some hesitation and a little backfiring upon hard acceleration last weekend.  After I ran it a while on the interstate I had no further problems but that was a red flag as to something needing to be done.  Should I change the plugs and wires or just the plugs or is there a more comprehensive "tune-up" regimen I should follow?

Thanks in advance for any advice.  It is appreciated!

Greg McDonnell
CLC#20841
Greg McDonnell
CLC #20841

TJ Hopland

I always get nervous thinking about something like a spark plug (especially in an aluminum head) for 10 years or 100K.  They may last that long but are they going to come out when you want them to?   I would be tempted to do it just because of the age.  Maybe see what there is for filters?   Is the fuel pump making any unusual noises?  These engines were known for nasty carbon build ups when they were only used for short trips, GM even came up with a special procedure to try and clean them.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Rusty Shepherd CLC 6397

#2
Greg,
I would definitely change the spark plugs and wires.  Those are the most common source of misfire and/or backfire on a Northstar.  I've experienced that problem and solution on my Northstar cars and on a senior neighbor's and all of them had significantly less than 100,000 miles. Plugs wires particularly deteriorate over time. Even though they cost more, be sure to get at least the plugs (AC platinums for your year model) from the dealership; those engines don't run properly on generic plugs.

Greg McDonnell

Thanks guys for your input!  My inner voice has been telling me for the last few months I probably should have changed them long before now.  I do want to say I maintain the car (I think) quite well and twice since purchasing it, have had the fuel system professionally cleaned.  The method used was sort of like an i.v.-it dripped a solution into one of the vacuum tubes while the engine was running.  It helped tremendously.  I was amazed at the pickup and power the engine had after the cleaning. 

As for the tune-up, should I do anything else besides changing the plugs and wires?  I will definitely use the AC/Delco Platinum plugs that you suggested Rusty!

Greg McDonnell
CLC #20841
Greg McDonnell
CLC #20841

David #19063

Hey Greg,

ONLY use wires bought at your Cadillac Dealer as well.  They are pricey, I think mine were $171 for the set for my '96 Concours when the tune up was done at around 81,000 miles.  Fixed the micro hesitation and micro miss I noticed.

My tune up was done at a local shop as they are much better mechanics than at the local Cadillac dealership (that went out of business a couple years ago...hard to believe but it did).  And this local shop flatly refused to use any other wires on a Northstar as they said that it was inviting trouble to do so.  In fact, they would not tune up the Northstar without using the factory wires and plugs.

One thing to also note when you buy (or your shop) buy the Northstar wires, check the date code on them as sometimes they wires can already be several years old.  Time does degrade them even sitting new on a shelf.  Get the newest wires you can, even if they have to order more or you have to call every dealer in 500 miles to fine newer ones.

David
David #19063
1996 DeVille Concours

Greg McDonnell

#5
I got the AC platinum plugs and wires today along with a new fuel filter.  The mechanic who did the work said the plugs were easy to get out (even after being in the car almost 10 years).  The only problem he had was accessing a few that were more difficult to reach at the rear of the engine.  The plugs weren't fouled or anything like that but definitely had a 'used' look to them!  LOL! He agreed the wires ought to be changed too given their age. The fuel filter also needed to be changed.  As a test, the mechanic poured a small amount of clean gas through it and it left a stain on the white cloth he used to catch the gas coming out the other end.

The weather was bad here today so I just took the car directly home.  Was quick, responsive and, as usual, a pleasure to drive. 

Thanks for all the advice guys!  I really appreciate it!

Greg
CLC#20841 
Greg McDonnell
CLC #20841

Rusty Shepherd CLC 6397

Greg,
I know that was an expensive 'tune-up', but it'll probably be the only one you'll ever do to that car and you definitely don't want any car (especially those with catalytic converters) to backfire, even occasionally.  It should run like a scalded dog now when you need to step on it and will run better and more economically the rest of the time. Northstars aren't perfect, but they're smooth, powerful, and reasonably economical.

Greg McDonnell

Rusty,

I agree, I hope I never hear that car backfire again as long as it is in my possession.  It does sit a lot but up until last weekend, has never done that before.  I did put a fuel system cleaner in the tank but I also filled the tank after adding it.  It may or may not have had anything to do with the backfiring.  As I mentioned in another post, I did go ahead and run it on the interstate after the backfiring and I was able to get things 'blown out'!  It ran smoothly after that.  The experience did get me to thinking about the plugs and the amount of time they had been in the car.  So all things considered, it turned out to be a good thing. 

By the way, the tuneup was not all that bad-parts (that includes plugs, wires and fuel filter) as well as labor came to $346.72  It would have been a lot higher had I taken it to the dealer! 

Thanks again for your advice and interest!

Greg
Greg McDonnell
CLC #20841