Spark Plugs and wires?

[jeepgclwj]

I was looking at my owners menu and it doesnt say you have to change plugs and wires till 100,000 miles. Is this true? Ihave 77,000 miles. If I were to change them any recommendations on brand. I want my car to run the best and I know the aint broke dont fix it rule but, new plugs and wires cant hurt. Any thoughts?

[richtazz]

Don't believe that 100k stuff. My car (99GT) had 73k on it and was in bad need of plugs and wires. The rear bank was wasted, the front looked better, but were ready also. If your car gets a lot of stop and go driving, it's due.

[troy1]

Hey Richtazz not to jack the thread, but what did 99 GT's come with for plugs, Platinum or Irridum?


Troy

[BNaylor]

Hijacking threads is a

But to answer your question the '99 GT, '99 GTP and '99 SE with L36 all came from the factory with AC Delco Platinum, 41-921.

[MVGTP86]

When you do change your plugs dont put platinums back in....thats a big no no for boosted engines...Use autolight cooper core spark plugs instead i would go with a 104 heat range. Platinum plugs retain heat and can create knock.

[BNaylor]

Originally Posted by MVGTP86

When you do change your plugs dont put platinums back in....thats a big no no for boosted engines...Use autolight cooper core spark plugs instead i would go with a 104 heat range. Platinum plugs retain heat and can create knock.

I disagree since he has a stock GTP. There is no reason to run the Autolite Copper Core brand on a stock GTP or one with no mods. The Platinums and Iridiums last longer and are reliable. Also, he could use Autolite Copper Core but the 606 or 605 are the better heat range for stock. The 104 and 103 should only be used when you are running a smaller SC pulley (3.5" or less) or are getting noticeable amounts of knock retard (KR) based on testing. There is no need to run colder spark plugs unless you have to.

[richtazz]

Just a note, the 41-921 was replaced by the 41-101 Iridium. I also agree with Bob that they are the best choice for un-modded engines.

[BNaylor]

Actually the AC Delco Platinum spark plugs are still available. Now called the Rapidfire 14. Some people claim that they have good luck with them but I didn't. Out of 6, 3 had cracked ceramic insulator with carbon tracks within 3K miles of operation. Symptoms: Blinking SES light, fixed misfire DTC P30X.

[richtazz]

I agree on the rapidfires Bob, I had a set given to me as a demo (for my Cavalier convertible), and I wasn't impressed. I would strongly suggest sticking with the 41-101 Iridiums, or if not available in the area, go with the Autolite Double Platinum APP606.

[BNaylor]

Originally Posted by richtazz

go with the Autolite Double Platinum APP606.

Why the Autolite Double Platinums? The single electrode AP606 or AP605 work fine and you can't beat the Walmart price and packaging deal. I'm running the Autolite AP605 Platinums in my Regal GS. Got them back when gas prices were high and they are one range colder so it is safe to use mid-grade fuel when I have to. No KR over 2 degrees running mid-grade. Less than 1 degree with premium at WOT. Confirmed by Autotap.

I run Autolite Copper Core 103 in my GTP due to the 3.0" SC pulley and fairly moderate mods.

[richtazz]

I suggest the double platinums due to the fact that GM's waste spark DIS ignition system is hard on the ground electrodes of single platinum plugs. For longevity, they seem to work better, as the single platinums get more ground electrode erosion over time (they only have platinum on the center electrode, where double platinums have it on both).

[BNaylor]

Originally Posted by richtazz

I suggest the double platinums due to the fact that GM's waste spark DIS ignition system is hard on the ground electrodes of single platinum plugs. For longevity, they seem to work better, as the single platinums get more ground electrode erosion over time (they only have platinum on the center electrode, where double platinums have it on both).

I see Rich. Understandable. So both the ground and center electrodes are Platinum versus just the ground electrode. Interesting, we shall see. I have 19K miles on the AP605s and no noticeable wear to date and gap is still at .060". If they make it to 50K miles I'll be happy considering it is a less than $2 spark plug. The double Plats are alot more expensive.

[richtazz]

Yes, they have a single ground electrode with a platinum disc on both the ground and center electrodes, versus the platinum disc on only the center electrode on the single platinum design(AP606). They are not a gimmicky multi-ground electrode plug like Bosch +2/+4's (<----JUNK).

[MVGTP86]

Originally Posted by bnaylor

I disagree since he has a stock GTP. There is no reason to run the Autolite Copper Core brand on a stock GTP or one with no mods. The Platinums and Iridiums last longer and are reliable. Also, he could use Autolite Copper Core but the 606 or 605 are the better heat range for stock. The 104 and 103 should only be used when you are running a smaller SC pulley (3.5" or less) or are getting noticeable amounts of knock retard (KR) based on testing. There is no need to run colder spark plugs unless you have to.

It all depends on your specific engine in your GTP too...Mine came from the factory stock w/ 2* of knock, I switched to a copper core spark plug and opened up the exhaust a little and it fixed the problem. I have a powertuner and have scanned/tuned several GTP's and have seen knock on stock engines as much as 2-3*, several times i have changed the spark plugs only and it has helped the knock problem a lot. Even if he has small mods such as a basic Open-cone intake and maybe pushed the boost by-pass valve down it wouldnt be a bad idea to switch to a copper core plug. Especially if he plains to get a reprogrammed computer or drop down to a 3.5 or 3.4 pulley any time soon. Putting the 605's would probably be better than 104's on a stock engine, i still believe from my testing and experience that platinums shouldnt be used at all on boosted engines. Just my .02 cents though.

[BNaylor]

Originally Posted by MVGTP86

It all depends on your specific engine in your GTP too...Mine came from the factory stock w/ 2* of knock, I switched to a copper core spark plug and opened up the exhaust a little and it fixed the problem. I have a powertuner and have scanned/tuned several GTP's and have seen knock on stock engines as much as 2-3*, several times i have changed the spark plugs only and it has helped the knock problem a lot. Even if he has small mods such as a basic Open-cone intake and maybe pushed the boost by-pass valve down it wouldnt be a bad idea to switch to a copper core plug. Especially if he plains to get a reprogrammed computer or drop down to a 3.5 or 3.4 pulley any time soon. Putting the 605's would probably be better than 104's on a stock engine, i still believe from my testing and experience that platinums shouldnt be used at all on boosted engines. Just my .02 cents though.

You are entitled to your opinion and two cents worth but minds will differ and you will get replies that disagree, especially in this forum.

If you are or were getting knock retard in a specific engine based on accurate means of testing then that is called an idiosyncracy but not because the L67 engine was not designed to run on Platinum spark plugs but if you make it a general recommendation to other GTP owners especially if they are box stock not to use Platinums then the suggestion will be open to debate and criticism. There are thousands and thousands of GM cars with L67 engines not just the GTP but other GM makes like Park Avenue Ultra, Regal GS, Bonneville SSEI that use Platinum or Iridium spark plugs with insignificant KR of less than 2 degrees. Fuel grade and quality will affect KR.

Based on my extensive tuning experience with the L67 which spans 10 years I still disagree that Platinum spark plugs should not be used. As a matter of fact they can be used in modded engines. The only time I have seen where Platinums should not be used is when using a NOS system.

The primary reason why most GTP owner use Autolite Copper Core 605-103 to control knock retard is due to supercharger pulley mods in which you will get KR much higher than 2 degrees without dropping to colder spark plugs and without intake, exhaust mods and PCM mods. Intake and exhaust mods are superior in controlling knock retard. Headers is the most significant KR reduction mod/tool less going to an intercooler. A bigger throttle body reduces KR.

The second reason why a GTP owner will switch to the Autolite Copper Core if getting concernable KR is due to the fact that they do not know what the colder AC Delco Platinum spark plugs are and everyone recommends the ALs so they use them. They just happen to be copper core. The Autolites have an easy to remember numbering system and plenty of published data on what the colder range progression is. So ALs are a logical choice and the cost is reasonable (cheap). The primary factor why I use AL copper core in my GTP is they are inexpensive and I change out more frequently than normal. Typically they only good for 25K miles before they degrade significantly.

GTP L67 engines were delivered with the OEM AC Delco 41-921 spark plugs up until at least the 2001-2002 model years. The 41-921 are double Platinum and made to last to 100K miles. Older tuners like myself know and remember the colder AC Delco Platinum spark plugs that are still available and used today. See below:

AC-Delco "double platinum" plugs:

Stock..........41-921
1 colder.......41-932
1-1/2 colder..41-919
2 colder.......41-913

Starting gap all at 0.060"