: Changing spark plugs on a Northstar



dstarr
08-04-07, 09:34 PM
The 99 Deville is up to 95K miles and the engine was beginning to run rough. The check engine lite came on. Pulled the Diagnostic Trouble codes and found one that says "cylinder missing" and another that said "engine stalled once or twice" and a couple of others that meant ignition troubles.
I first thought about having my friendly local garage change the plugs after looking at the engine. The cross wise mounting puts one bank of cylinders right up front and easy to get at, but the other bank of cylinders is up against the firewall and buried under a load of stuff. I finally decided that I'd have to turn in my shade tree mechanic's license if I couldn't even change the plugs on a V8.
So, picked up 8 Autolite plugs and some antiseize compound at the local auto parts place. Asked the counter man about the Autolite for a Caddy, Autolite used to be a Ford brand. Counterman says that's all old fashioned and now GM cars are speced for Autolite as well as Champion and AC.
Got the front plugs swapped out no trouble. They needed a change, the center electrode was damn near burned away and the gap was double that of the new plugs. Then I tackled the ugly rear plugs. It wasn't as bad as I feared. Take off the plastic engine cover, and the cross member running between the spring towers and the rack of ignition coils. Then you can get a 1/2" drive deepwell socket onto the plugs with room for the rachet handle to swing. And they did come out with out busting anything. Whole job took about three hours.
Tools required. 1/2" drive rachet handle and 6" extension. 5/8 inch deep well socket. 1/4 drive rachet handle, 6 inch extension and a 10 mm socket for the bolts on the coil rack. 1/2" socket for the cross bar nuts.
Tricks. Take duct tape, fold it double sticky side out and press it into the deep well socket. This will stick to the plug and pull it up out of those deep deep spark plug tubes in the heads. Beats fishing for the old plug with long nose pliers.
Washed the black off my hands and started her up. Purred like a kitten.

David Starr

Gibbi
08-04-07, 10:28 PM
Thanks for the report. I will be changing mine soon even though I've only 69k on my 98. I think I'm going with the fancy Bosch with the 4 electrodes. They're costly but you don't change these things very often anyways.

afroney
08-04-07, 11:44 PM
Woah there... Do a little internet research on the Bosch Platinums. I installed a set in one of our Dodge Caravan's. They lasted about 1 year and 10,000 miles before the electrodes were completely worn out... According to my mechanic, Denso, NGK, or AC Delco platinum/iridium plugs are the way to go.

Gibbi
08-05-07, 08:28 AM
Didn't know that, I'll do a little research first, thanks. I did see that Bosch 4 is available in platinum/iridium now too. The iridium must be needed for longevity??

Zorb750
08-05-07, 09:59 AM
Forget the bosch. Their center electrode insulators are garbage. Go with NGK or Denso if you want an aftermarket plug. The $3 Denso basic platinum plug is better than any of Bosch's stuff. You can also not go wrong with AC Delco Platinums.

And to dstarr: Autolite plugs are worse. This is a Cadillac. Even used, it's hardly the most cost effective car you can buy. Why must people go cheap? I'm all for saving money, which you are by doing the work yourself. Don't buy junk parts. Leave the Autolite to your leaf blower.

Ranger
08-05-07, 10:44 AM
I seem to recall the Guru once telling about someone using Autolite on a Northstar and the engine blew up. Something about the wrong heat range or something like that. Autolite would not stand behind it. I'd stick with A/C Delco.

Gibbi
08-05-07, 11:12 AM
I've read a number of threads now for research and I'm now going with 41-950 AC/Delco's. Cost vs performance it appears to be a no brainer! Got all three volumes of FSM coming from ebay, $45 including shipping, so I'm gonna get a whole lot wiser soon.

dstarr
08-05-07, 04:48 PM
Forget the bosch. Their center electrode insulators are garbage. Go with NGK or Denso if you want an aftermarket plug. The $3 Denso basic platinum plug is better than any of Bosch's stuff. You can also not go wrong with AC Delco Platinums.

And to dstarr: Autolite plugs are worse. This is a Cadillac. Even used, it's hardly the most cost effective car you can buy. Why must people go cheap? I'm all for saving money, which you are by doing the work yourself. Don't buy junk parts. Leave the Autolite to your leaf blower.

On parts, I tend to go with what the counterman at my local auto parts place says will fit. It's his day job, and he probably knows more about it than I do. Parts is parts. I only do this stuff occasionally, he does it every day. Autolite has been around for ever, they used to be owned by/associated with/married to Ford. I've had several Fords over the years and they all took Autolite, they all ran fairly well, and lasted a long time.
Modern electronic ignitions (like Caddy) are so hot that they will fire the cylinder even with badly worn plugs with a gap way too wide. It's the electrical zap from the coil[s] that sets the mixture off, not the metal in the plug electrodes. It also keeps the plugs clean. Even with 95K miles on them, the old plugs were clean as a whistle on all eight cylinders. A little eroded, but clean.
Took the car out for a drive today. The "Check Engine Soon" light went off all by its self, and the Northstar pulled me up three mile hill running smooth as silk. I'll reset the history DTC's tomorrow. Instantaneous indicated gas mileage was up. Should have changed those plugs back about 20K miles ago.

Submariner409
08-05-07, 06:36 PM
:rolleyes: If you're new here, and dig back a couple of years, you'll read horror stories about Bosch plugs and N*'s. AC 41-987 (late N*) platinum electrode is made in Japan, so now we know where Denso went (Denso is the plug named in my '02 STS manual....)

Zorb750
08-06-07, 02:30 AM
On parts, I tend to go with what the counterman at my local auto parts place says will fit. It's his day job, and he probably knows more about it than I do. Parts is parts. I only do this stuff occasionally, he does it every day. Autolite has been around for ever, they used to be owned by/associated with/married to Ford.
...


No. Parts are not parts. Champion was/is Ford. The parts counter guy is not a mechanical expert. He is a monkey who works for an auto parts store. He knows what will fit, probably not much beyond. I love when some old school grease monkey tries to tell me things I can do to make my car run better, prevent a problem, or fix a problem. I tell him "This is a Northstar V8, not a 1965 Chevrolet 350. My engine's more complicated than a lawn tractor engine." Believe it or not, my Cub Cadet's engine is about as mechanically complicated as the afore mentioned 1965 Chevrolet. It has a carbuerator, a fuel pump, all the filters, a vacuum actuated AND a manual choke, an overspeed governor, overhead valves actuated by rockers connected by pushrods to a chain driven cam in the center of the engine parallel to the crank. It even has a pressurized oil system with a full flow filter.

ewill3rd
08-06-07, 06:37 AM
Do not use Bosch platinum plugs in any GM car. They might seem to work great for a while but it won't take long to develop some drivability issues. Heat range is pretty darn important on the plugs, at least in a GM car. If it is too far off the car will never run right.
No real reason not to use Delco plugs that were designed for the application.

Also you can buy "spark plug sockets" that have a rubber sleeve built into them that are designed to hold onto the plug when you pull it out and slide off the plug once it is tight. They are not too expensive.
I use a "locking" extension that holds onto the socket so it all comes right back out.

jadcock
08-06-07, 12:27 PM
I pulled the original plugs out of my '97 SLS at 145k miles (or thereabouts), just to say I changed them. The car didn't run much different after the change...and it ran fine beforehand. There was a little gap widening, but not bad...especially for plugs with well over 100k miles on them. I replaced them with ACDelcos.

And by the way, I used to work at Advance Auto. To the person who said that the counter guy at the retail store is just a monkey working at a parts store...YOU ARE CORRECT. There is NO mechanical knowledge required to work at those shops. Most of us did it because we liked cars, but would absolutely sell you a Champion plug for your Northstar because it worked good in a buddy's friend's cousin's little baby brother's Mustang. Nobody knows anything about the Northstar engine at those places (I sure didn't when I worked there). Parts isn't parts!

z06bigbird
08-07-07, 05:04 PM
Parts guys are not nearly as dumb as they look. That is what the mechanics at my dealership tell me.

LOL

codewize
08-08-07, 12:56 PM
From what I understand Bosch plugs suck in the N*. AC Delco OEM plugs provide the best performance.

Don't waste your money.

tateos
08-24-07, 08:17 PM
I Have Had Good Luck With The Oem Ac Delcos - Don't Really See A Need To Try Something Else - Imho

fixitagain1
08-24-07, 08:34 PM
Hey I also have a 99 seville with the same problem....gonna start swapping plugs tomorrow fingers crossed thats whats wrong ...quick question for you about resetting / getting engine error codes off the car....how????

Ranger
08-24-07, 09:33 PM
See the "sticky" in the Tech Tips section.

nigelb
08-25-07, 12:24 PM
the FSM says that the motor can go for 100k miles before the plugs need changing, thats by using the recommended OE plugs.
the fact that GM would say their plugs can last 100k miles is good enough reason for using them.
would bosch stand behind such a claim?

jimfulco
08-28-07, 04:26 AM
My AC platinums died with only 70K or so (they came in a used engine). I put some basic everyday Champions in and they work fine.

Using a magnetic spark plug socket makes the whole job a whole lot easier. I paid excess bucks for one off a famous-brand tool truck, but you can get one for <$10 from one of the mail-order joints if you don't mind the wait.

Dadillac
08-28-07, 03:10 PM
I paid $5 for my spark plug socket, and it works great for the N*. I got it from www.harborfreight.com. It is an extended socket that is about 5 or 6 inches long. To retrieve it from the spark plug hole, just use a pair of needle nose pliers. The socket and the holes are the same depth.

Don

jh225
08-29-07, 12:02 PM
I paid $5 for my spark plug socket, and it works great for the N*. I got it from www.harborfreight.com. It is an extended socket that is about 5 or 6 inches long. To retrieve it from the spark plug hole, just use a pair of needle nose pliers. The socket and the holes are the same depth.

Don

Don't use a needle nose pliers or any other pliers, why risk cracking the plug or scuffing the head?

Changing plugs on a N* is simple.

Just loosen all the plugs with a plug socket, and leave the plugs in the holes. Then take a 12" piece of 3/8 fuel line, stick it into the plug hole, over the plug, push it on a little bit and pull the plug out.

Installation is reverse of above.

This is actually the way I change all plugs in any car. No chance to screw anything up, and you can easily get the threads started without crossthreading.

Dadillac
08-29-07, 08:49 PM
Don't use a needle nose pliers or any other pliers, why risk cracking the plug or scuffing the head?

Changing plugs on a N* is simple.

Just loosen all the plugs with a plug socket, and leave the plugs in the holes. Then take a 12" piece of 3/8 fuel line, stick it into the plug hole, over the plug, push it on a little bit and pull the plug out.

Installation is reverse of above.

This is actually the way I change all plugs in any car. No chance to screw anything up, and you can easily get the threads started without crossthreading.

No chance of breaking the plug or scuffing the head. The socket is even with the top of the head, and you only need a little pull to get the spark plug out of the rubber insert in the socket. It is faster than using a rubber hose. But thanks for the input.

Don

Rafterd
10-02-07, 10:34 PM
Well I have always been the guy that dances with the girl who brought me.
While working on the STS I will use AC Delco. If working on my Ford Diesel Piuck up, I use Motocraft. My wifes Dodge Diesel Pick up gets Mopar. That is the parts they come with and seem to last the longest.
My 2 cents
Bill

willseville
11-05-07, 02:50 PM
I read some posts here, and I agree completely about original parts for replacements.

So I just bought original plugs AC 41-902 here in France for my 1992 Seville 4.9L, And I don't know what is the gap...

Is it possible for somebody to give it me ? I searched in the books , and I have no shop manual, I will order one !

Thank you !

muzizman02
11-05-07, 04:20 PM
ya don't use bosch the ac or champs plugs cost too for this car and work very well.leave the bosch plugs for the bmw's and such

willseville
11-05-07, 04:30 PM
Muzizman02,

I agree, my Cadillac I purchased last 16th october, is going to run only with original parts !

Is somebody here able to give me the gap for my new plugs I have to change tomorrow.
It is written on the box, like you know " set the gap with vehicle specification"

It is the first time for me, and I don't want to brake something...

Thanks !

Submariner409
11-05-07, 05:21 PM
willseville,............the spark plug gap is .050".

Perhaps someone with a 4.9 can give you more details........look in the other engine forums, as 4.9 is next one down from N*.

Ranger
11-05-07, 05:27 PM
I read some posts here, and I agree completely about original parts for replacements.

So I just bought original plugs AC 41-902 here in France for my 1992 Seville 4.9L, And I don't know what is the gap...

Is it possible for somebody to give it me ? I searched in the books , and I have no shop manual, I will order one !

Thank you !
Plug gap is .060
Northstar is .050

willseville
11-05-07, 06:46 PM
You are great !

Thank you so much to you, Submariner409, and Ranger !
Tomorrow afternoon I am going to change it, and just after, when hot, oil and oil filter, I bought a "PF 58 " AC oil filter.

A bientôt !
Will.

PS : sorry for my mistake : "I don't want to "break" something", sometimes I write like I hear.

willseville
11-06-07, 01:35 PM
One more time great thanks to you !

I have changed my plugs this afternoon, my Cadillac runs very well, idle is very good now, there was waves before, even on the road, at 80 km/h for example.

You are going to understand because the car did not run well before, I never have seen that in my life :
The last plugs AC had ... 1.55 instead of 0.60 !!! mounted from the box to the engine.:annoyed:

I wait for my air filter, and gas filter, and I will look the ignition cap, wires are good.
And the evening, it is 6.20 PM here, my car gives its power, with a very nice V8 "music", smooth and very comfortable to drive.
I am very glad.

It was very funny to place the plugs under the windscreen engine side, I was on a carpet, on my engine:lol:

It is easy to do, with good tools, I am a quiet guy, one hour to do that job.

cadillacrick
11-13-07, 12:52 PM
I'm not sure how to feel about this......I called a couple of shops to see what the price would be just to supply the labor to change the plugs in my 1993 Northstar, Seville. The costs range anywhere from $110-$145. They all said it was about 1.5 hours for labor. I just changed the plugs in 30 minutes. WTF?!?!

Don't get me wrong, I don't paying.....but that's getting a little outrageous!

Submariner409
11-13-07, 04:32 PM
Changing the spark plugs in a rate shop is priced on the published time charged for the average repair.

Depending on the speed of the mechanic, its entirely possible to complete a job in less than half the "accepted" time.

In other words, its routine for a shop to bill 2 jobs which were completed in half the time required, gaining the shop "double time".

ewill3rd
11-13-07, 09:49 PM
Flat rate is kind of goofy for plugs and wires.
It is like .4 for one and then .2 for each additional or something.
Labor is not usually added in time guides for both.
I think I usually charge like 3 hours or something to do plugs and wires together.
Of course that depends on the year and model. Some N* engines don't have wires at all, but the coil packs can be a nightmare to get off if they have AIR.

You have to remember flat rate is based on book time, not necessarily actual time.
There are things that can make it take longer than what the book shows.
It is a broken system but that is what the industry goes by. The total cost will vary based on local labor rates.

Ranger
11-13-07, 10:30 PM
I think I usually charge like 3 hours or something to do plugs and wires together.
How does that work? I thought you got what book calls for and the dealer has a flat rate. Are you saying that each tech sets his own prices and any given job could vary depending on who does it?

ewill3rd
11-14-07, 09:55 AM
Ranger, sometimes yeah that is how it works.
I use the book as a guide and add or take things away based on how much diagnosis I have involved and if I see other things that need to be handled along the way.
There are things the book doesn't take into account.
I always try to be fair and I usually end up selling myself short to be honest, but I want my customers to get their maximum quality of work for their dollar. Sadly there are guys in the industry who don't play fair.
Some guys take the book time and indiscriminantly add to it for whatever reason.
I have seen guys try to charge as much as twice the book labor for a given job.

It can vary from car to car, based on circumstances as I described.
It is kind of hard to explain, but I think you get my point.
What it boils down to is to give an estimate I like to have the car in my stall to see what I am up against when I check the book time and figure how much time I am really going to need to fix the car.

I'd be the first one to admit the flat rate system is broken.

Cadillacattack
03-20-08, 04:28 PM
On the 1996 Northstar the front plugs came out in a jiffy. The rears look harder, but come out in a snap. I had no need to remove any coil packs or covers. Just a good steady hand. As for the plugs to use it is best to do as the slogan says. Keep your car all GM. So the best bet was to use the AC Delco 41-950 plug. These plugs aren't cheap like they used to be close to 6 smackers a piece from the auto parts store. However they will last a long, long time. The specs are what is needed for original performance.
Professional are designed to meet increased performance and reliability requirements while satisfying drivers who demand the best.
Features include:

Dual tip provides outstanding performance and exceptional durability
Ceramic insulator is nearly diamond-hard and provides added strength and shock resistance
Nickel/chrome alloy electrodes resist wear from gap erosion and corrosion for maintenance-free service
Hot-tip insulator heats fast and fires hot to resist fouling
Copper-core center electrode fires hot to resist fouling and improve heat dissipation
Fits older engines that originally used conventional plugsHope this helps.

Submariner409
03-20-08, 06:30 PM
Considering that this is essentialy a dead thread, I doubt it. All been covered many times.

stngh8r
03-25-08, 07:09 PM
Cadillacattack: Thank you very much for your information. It was very helpful, despite Sub-Naysayer's opinion. I just bought plugs, but thank goodness I haven't put them in yet. I will take them back and exchange them for the 41-950's. The info you posted is the type of details I was looking for.

Submarine: I commend you for your knowledge of the N*, but for crying outloud man, you don't have to be so negative all the time.

khubla
10-14-09, 03:31 PM
There is a much easier way to change spark plugs on a Northstar engine. I just finished changing all 8 plugs on my 1996 Deville and did it in one hour including a short test drive. First here are the tools that you will need: A 3/8 " ratchet, a 12" extension, a 3/8 swivel end, a spark plug socket, a flashlight and a small telescopic magnet. You do not need to remove anything on the engine to access the plugs. The front plugs are easy and simple to change out. Now for the rear. The rear bank of cylinders are numbered 7-1-3-5 and starting on the left side facing the firewall is #7. You will need to position yourself on top of the engine to see behind the distributor. Remove the 2 distributor wires over #7 to access the S. Plug wire end directly below, pull out the plug wire and remove the plug with your socket set. Replace the S. Plug and before moving to the next plug replace the two distributor wires you removed. Repeat this process. The magnet is handy for placing the new plugs back in the plug well. The last plug, # 5 does not require removing any distributor wires.

Submariner409
10-14-09, 04:03 PM
Check your plug numbers and wire connections. Your rear bank sequence is wrong, and you should remove and clean the entire coil pack and ICM contacts (pre-2000) or both cassettes (2000+) - no distributor in a Northstar.

Ranger
10-14-09, 05:06 PM
Distributor? Are we talking about a Northstar?

bammer21edm
05-06-13, 02:35 AM
I am about to change the plugs on a 98' Deville. I notice the local Walmart carries Champion platinum. Would be these okay?
Or do I go to the dealer and pick up Delco plugs at a slight premium? Thanks

maeng9981
05-06-13, 03:05 AM
Stick with AC Delco Platinum 41-950. Rockauto has them and is offering rebates. Even without rebates 8 AC Delco plugs are just $40 or so.

rodnok01
05-06-13, 01:23 PM
Ac only or it'll hate you. Aftermarket plugs last a short time then you will get misfires and you'll spend as much anyways fixing the problem. The guy who owned my 98 before me put 99 cent plugs in fried a coil then sold to me cheap. I put ac plugs back in and it runs like a champ.
I put el cheapos in my 99 PA and fried a coil after 6 months maybe due to resistance in the plugs so I learned the hard way too.

JoeTahoe
05-06-13, 01:31 PM
A/C Delcos all the way

JoeTahoe
05-07-13, 12:25 PM
Rock auto has A/C Delco platinum for $4.58 ea with a mail in rebate for $1.50 ea