: Spark Plug question for N*

06-02-04, 02:09 AM
Ok, I've seen posts recently about spark plugs for these engines costing fifteen bucks a pop, but when I look them up on the napaonline.com website, it says Bosch Platinums are only $2 apiece, up to 6 for the +4. I'm heading out on the looong roadtrip in a coupla days and figure it can't hurt my fuel mileage if I replace the plugs, but which do I use? I'll eventually learn enough about this darn car to not be posting a new question every day, but I'm not there yet!
Thanks a bunch,

06-02-04, 02:35 AM

So far, what I've gathered is that most users on the forum like to use OEM products, Myself included, as these were the parts the engine was designed / validated with. No unexpected suprises, et cetera.

The OEM Plugs are supposidly good upto 100k or so..
Hell, I'm probably off.. but much closer than you - lol - kiddin'
Feel free to chime in and correct me, anyone.. Beuller, Anyone..

Guess it's like the "Which motor oil is better" debate
Have a safe trip..


06-02-04, 11:59 AM
Nothing wrong with the Delco double platinums. What was the cost on those?

06-02-04, 12:40 PM
Double's were like 299 or 399 a piece, less than five bucks...Guess I'll go with them. I'll pick 'em up before work and throw them in after...Ok, are the other plugs underneath the engine cover somewhere? I havn't had that off yet, so I'm guessing they are, but I want to be sure before I go ripping everything off to try and find them.

06-02-04, 02:12 PM
They are in the center of the heads. You will see the 4 plug wires going to the plugs. There are some threads about changing plugs and also about tuneups.

Bbobynski did an excellent run down on a tune up but you'll have to look for it as I didn't save it.

08-15-04, 10:47 PM
Greetings ,
some input on plugs

1) get a digital ohm meter
2) pick a few plugs at the place where you buy plugs.
3) puting the needle of the meter on the tip of plug and the other on the top of the plug.(Not the very tip, the inner tip where the white porcoline is)
4) get a good contact and read what the meter says

example : 4.15k is 4,015k ohms
1.5k is 1,500k ohms

5) the LOWER the #k ohm the more SPARK , meaning more combustion

Best plugs I found for my 99 Devile is the BOSH PLATINUM Line or Auto light Platinum. there IS A DIFERENCE IN PLUGS which is in direct perportion to performance and mpg, i get about 29-30 mpg in the deville.

NOTE: Do the same thing to the wires for your cady , get longest wire and test by both ends read the meter, same thing ,lower is better.

Best ones i found so far was the Splitfire ones , If they make it for the cady.
If not you can get a universal one from Splitfire, I think and make your own.
you will have to check that part out.
happy hunting

08-16-04, 12:18 AM
If the plugs in it look good and are properly gapped, leave them alone. Don't fix what's not broken. Why risk crossthreading something (especially in those aluminum heads) when they're working fine and probably don't need to be changed? It's very unlikely that new plugs are going to affect your mileage. If it's mileage you're after, make sure your air filter, PCV valve, stuff like that are in good shape, and there are no PCM codes.

If you do change the plugs, use a platinum plug of some sort. The engine was designed with AC Delco plugs in mind. Car manufacturers spend millions upon millions of dollars to keep fuel mileage up. Why would they skimp on a $3.00 item if it would affect mileage? The various brands, styles, etc., will make no noticeable difference in performance or mileage, so cut the risks and use what the manufacturer has tested in the engine. Gap them carefully. Use a torque wrench and be careful installing them to the right spec. Aluminum heads can warp if they're overtorqued, and then who knows what you might wind up with.

Good luck and happy travels...

08-19-04, 11:15 AM
You have a 94. If you haven't done so yet, take the plugs out and inspect them. Don't get scared about crossthreading. Just take your time. You have to get them out to check them. Do a search on the internet for spark plug problem identification.

When I first got my caddy, I took mine out to inspect. The platinum plugs that come in these northstars are usually good for at least 100,000 miles. My car had 90,000 miles on it. I knew their time was coming. When I got them out they didn't look too bad. However, one did have a hairline fracture in the porcelain. I replaced these plugs with Bosch Platinum2s. They work great. I cannot say they are any better they AC Delcos, though. I didn't compare the old Delcos with the new Boschs for gas milage.

You will get better milage if your plugs are really bad and you replace them with a decent platinum plug, though.

08-19-04, 01:29 PM
The ONLY reason that cacillac uses the platnium plugs is so they can claim the 100k mile tune up. Also if you go platnium make sure they are DUAL platnium (on the electrode and the ground) if you have the northstar engine because it double fires the spark plugs... (alternating current paths because of the 2 plugs to 1 coil). If you use regular plugs it eats them up, or single platnium it will eat it up because of the way it is designed.. A regular plug will work ( $1 plug) but it won't last 10k miles. Platnium actually conducts less electricity than copper, so the copper plug would make a better spark however it just won't last. again make sure they are dual platnium, the delcos work just fine. If you don't have a northstar engine you can pretty much use whatever you want (the 4.9 engine for example), unless they made a 4.9 with the coil packs (2 plugs per coil) which i'm not positive about. If yours has coil packs use dual platnium if you don't want to change the plugs every other oil change :>

08-20-04, 02:46 PM
:coolgleam Admittedly I spend most of my time on the Ford boards, but over there everybody who ever tried Bosches had problems with them.

08-20-04, 07:05 PM
I have about 16000 miles on them now. I will be taking them out to see how they look and to clean them up if they need it. I am about to replace my leaking radiator, change my drive belt, and replace one of my upper torque arms. I will check them then. I am getting over an issue of bad gas. See alternate thread: http://www.cadillacforums.com/forums/showthread.php?t=18690. I want to see if this had an effect on the plugs (from detonation).

08-28-04, 08:17 PM
I replaced the stock AC DELCO PLATINUM plugs at around 80,000 miles as they had started to misfire. I found that the plugs were definately burning a ton of oil as we all know N*'s do. Because of this fact with the N* engines it is extremely important to use a plug with a temperature rating at least as high as the stock ones from AC DELCO. If you use plugs with a lower temperature rating they will foul up from the oil in the cylinder that is being burnt, instead of burning the oil off the tip of the plug. This is why all spark plugs have a temperature rating on them. Depending on the engine and how many cylinders it has, if it is OHV, SOHC, or DOHC, and what the average operating temperature of the cylinders which is dependent on the efficiency of the cooling passages and system in the engine, all engines require different temperature spark plugs. I decided to replace the stock ones from AC DELCO with the BOSCH PLATINUM +4 plugs, which have a higher temperature rating than the stock AC DELCOs. As expected you can't physically feel any performance increase, but I would bet that there is some, maybe only a couple HP. It definately runs smoother now. Occasionally the engine would idle and run a little choppy if the car hadn't been opened up in a while as the plugs were probably fouling with oil, however with the BOSCH +4's it runs consistantly smooth now, especially up around redline, where you used to really feel it miss every now and then when it hadn't been run up there for a while. I would definately recommend these plugs. Although I can't speak on lifespan because I only have 116,000 miles on the car now, which is only about 36,000 on the plugs, but I think BOSCH guarantees them for 100,000 miles though.

08-28-04, 09:05 PM
What have you done to the ESC? I'm looking for anyone who has done anything at all to the NS engine because I want to mod the hell out of mine but i can't find much .. so if anyone cares to chime in let me know :) Any mods from stuff like intakes/tb to things like headers or removing egr, using a new intake manifold, porting heads, etc.. to things like NoS also :)

08-29-04, 01:40 AM
I checked my Bosch Platinum2s today after I replaced my radiator. They have 18000 miles on them. The #2 plug was the worst with some hard carbon build up on the ground electrode. I am thinking this is from possible detonation from the bad gas I had. All the plugs along the back side of the engine were in great shape. I cleaned them all and put them back in.