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New Spark Plugs


JasonA

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My 97, like all other 93-99 cars, says "Premium Required". I have run it on mid-grade before, but performance has suffered. It does run best on premium. That may change now with new plugs, I don't know.

In a slightly different angle to this topic, what damage could I do running the plugs at .050"? Even if .060" were correct, and that doesn't seem to be the case. I'd be much less confused if the gap on my old plugs were .080" or something, but since they're at OR LESS than the spec'd gap of .060", I know that's not what they were at when new, which doesn't match the sticker. Hmmph.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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You are keeping an open mind here thats good. Go to the source to get the info (Cadillac). I found this interesting reading to further confuse you: :lol:

Opening The Plug Gap:

On weaker or stock ignitions, opening up the gap CAN increase the spark kernel size, thereby creating a more efficient burn. The problem lies in that any added gap creates more strain on the other ignition parts.

Coils may not have enough stored energy to fire, or in the least case, not enough energy to cross the gap, creating a miss-fire.

Plug wires will break down due to the added resistance as the spark tries to reach ground.

Rotor and Cap, as well as points (if you still have an interest in prehistoric ignitions), and the carbon bushing in the center of the distributor cap will show early failures.

All of this is because the greater the gap and the higher the voltage requirement to jump the gap. Do not forget the gap between the rotor arm to the distributor cap too. A high performance rotor is a bit longer at the tip, allowing less spark loss or chance of spark scatter in the cap as the spark attempts to jump the plug gap.

As many of us know that race, it is also possible to slow down a car if the gap is too big. I will get into this later when I describe proper spark plug gaps.

Proper Plug Gapping:

Proper gapping of the spark plug is necessary to get maximum spark energy, lowest RFI release as well as what is best for the longevity of the secondary ignition components (coil, cap, rotor, wires, plugs).

When checking plug gaps, the correct way is to use ONLY wire gauges, though many of us are using the slider style gapping tools. These flat or feeler gauge style gauges do not accurately measure true width of spark plug gap. (ahem, I said this above, :lol: )

When increasing the gap size for our high performance applications utilizing advanced ignition systems such as Mallory, Accel, Jacobs, Crane and Holley ... it is important never to go more than plus or minus .008". This is to maintain parallel surfaces between ground and the center electrodes.

Something many do not know, is that with Higher Compression ratios and Superchargers as well as Nitrous, in many cases smaller spark plug gaps must be used as well as the use of a much hotter ignition system (see at link below). These higher cylinder pressures require more energy to jump the spark plug gap.

The rule of thumb on plug gaps is to open them up in .002" increments at a time. When the car (race vehicle) begins to lose power or slow down then go back .001-.002" and this in most cases is the optimum gap.

Good Reading:

http://www.centuryperformance.com/spark.asp

I guess the question is, what is your compression ratio compared to the compression ratios for the years that have the same spark plug? Hmmm... You could always put her on a DYNO! Anyone see a guru?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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You know, now that I think about it, when I did the plugs on my '97 I don't think I took out 41-950's. 41-929 comes to mind but I would not swear to that. Infact, I think I even posted about it. I think the 41-950's superceeded the original factory plug and that may be the answer to this mystery if my memory is correct.

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41-929 is what mine takes see the manual above and they are .050

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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My '98 Owner's Manual specifies 41-900 sparking bolts. The Service Manual says 41-929.

Both sources have dated information and I am running with 41-950.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Yes, I think the 41-950 has superceded most of the older part numbers out there. My old plugs are 41-950s. I guess I shouldn't claim that they're "original" plugs. The car came into the family at 42k miles, so it's possible these could only have about 108k on them, at the least. But I'm assuming they're original.

The bottom line is, I really don't care what the gap is. If it's supposed to be .060", fine. If it's supposed to be .050", fine, I'll re-gap them (removing them will be easy now!). If my original plugs had come out with gaps of .070" or more, I'd be perfectly happy with the .060" spec. What frustrates me is the decal on the car says .060", but the plugs that came out were even less in most cases...leading me to believe they were probably factory-installed at .050".

An interesting aside is the old Oldsmobile V8s used .080" gaps...up through 1985 I think. The roller cam 307s got different heads, and a plug gap of .060", but the older traditional Olds heads used .080" gaps.

Edit: upon further inspection, it's not accurate to say that ALL of the platinum pads had come off. The #8 plug still had the pad on the ground electrode. 149k miles! "Go #8!" <-- this is the only time I will mutter that phrase :)

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Jason, I went to Autolite.com and found this:

1997 CADILLAC SEVILLE

print | email this article

Autolite® Products

Engine Type V8-4.6L F/inj. (9)

Available Brand Name Part Number PlugGap Notes

Double Platinum APP104 .050 OE Style

XP Xtreme Performance™ XP104 .050

Platinum AP104 .050

Copper Core 104 .050

Pro-Fit™ 86642 Use until inventory is depleted

Professional Series 96642

Engine Type V8-4.6L F/inj. (Y) engine type?

Available Brand Name Part Number PlugGap Notes

Double Platinum APP104 .050 OE Style

XP Xtreme Performance™ XP104 .050

Platinum AP104 .050

Copper Core 104 .050

Pro-Fit™ 86642 Use until inventory is depleted

Professional Series 96642

Mike

post-2998-1136944114.gif

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thats a good idea, both the Champion and Autolite sites show .050 gaps, of course as Murphy's Law would have it, AC Delco doesn't show gaps. I would be amazed if .060 is correct, nothing that we have seen points in that direction other than the manual and the under hood label which normally would be good enough for me... If I get a chance tomorrow, I will go to my local Caddy dealer (one mile away) and pick their brain...

post-2998-1136945665.gif

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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http://www.acdelco.com/html/catalog/index.htm

EDIT.......

That link might not work; but, from the ACDelco home page you should be able to find a "Vehicle List By Part Number" selection.

Put the #'s in that page and you will see what ACDelco has to say about 41-900 and 41-929.

Paydirt on the 41-950.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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JIM you are a genius! Ac Delco states the gap is .050 also! WOW!

1997 CADILLAC SEVILLE SLS V8 4.6L 281cid GAS FI N Engine VIN = Y

Qty Req Qty ACDelco Part# Description

IGNITION / SPARK PLUG

08 41-950 SPARK PLUG, PLATINUM PLUG

GAP .050

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks guys -- so far, I have three people with '97s who say their decals indicate .060" (some on another board), and everyone else, including ACDelco, saying .050". Not sure what I'll do...I'll probably take them out and gap them at .050" like I THINK my originals were gapped at...and that would match what everyone else is showing...still odd that Cadillac tells me to gap them at .060".

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Jason see this link, this may shed some light as to why we are seeing different gaps maybe it was originally .060 and subsequently changed to .050, see this, I will look for other bulletins, Mike

http://www.acdelcotechconnect.com/pdf/tsb/tsb_03D-J-171.pdf

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Jason

I just checked out RockAuto for the correct plug and they list AC 41-950 with a gap of .050". You got me thinking and I went out and checked the old plugs and the worn gap was .060". I set my new plugs at .050"

I just looked under my hood and I have no sticker anywhere?

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The sticker shound be on the hood - when you open the hood, look at the front edge. I just checked the underhood sticker on my '96 and the gap spec is .050. I don't know why the '97s would be .060 but I wouldn't lose any sleep over it as long as the engine is not misfiring....

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I found the miss I had...after trying a few of the rear plugs the first time and not being able to get them out. I was re-inspecting my old plugs tonight and as I picked up the #1 plug, it rattled. Yes, rattled. I can spin the porcelin insulator inside the metal plug casing (where the hex head and threads are). I can't spin it completely around, but it's definitely loose. It won't pull out, but it's obvious that was the source of the miss. The #6 plug also had a small crack in the porcelin.

I am officially convinced that 149,000 miles is/was too long for those plugs. :)

I plan to do a write-up on the process, and to emphasize how important it is (or was for me at least) to procure the proper tools. The small 3/8" drive universal joint that I was trying to use on the rear plugs was not only not providing enough action on the plugs, but maybe damaging them in the process. With the proper universal joint and heavy duty extension, they popped right out.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Do you think the porcelin insulator was loose enough to lose compression?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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No, I think it was loose enough to provide an electrical disconnect. A dead plug. I was talking about the porcelin insulator on the outside of the plug -- where the plug boot connects. The ceramic insulator on the underside of the plug, that supports the center electrode, seemed solid.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Just to follow up, as I posted in another thread, I received this answer from a "reputable source":

The spark plug manufacturer and supplier has changed several times. The gap changed a little with the specifics of the spark plug supplier and their production process as I recall. Either .050 or .060 is really OK....not that big of a deal with that type of plug. .060 is the better gap as (generally speaking) the larger the gap the greater the arc and the greater the chance of contacting something combustable and starting ignition. If there is any doubt about the longevity of the platinum pads (as you noted) then the desire might be to run .050 so as to not have too great of a gap at .070 (which is starting to push the capability of the ignition system). As the platinum pad retention improved and the plug quality and process control improved over the years the gap could be allowed to creep up.

Based on this answer, I'll definitely keep my new plugs at .060".

Thanks everyone for their contribution to this thread.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Just to follow up, as I posted in another thread, I received this answer from a "reputable source":

The spark plug manufacturer and supplier has changed several times. The gap changed a little with the specifics of the spark plug supplier and their production process as I recall. Either .050 or .060 is really OK....not that big of a deal with that type of plug. .060 is the better gap as (generally speaking) the larger the gap the greater the arc and the greater the chance of contacting something combustable and starting ignition. If there is any doubt about the longevity of the platinum pads (as you noted) then the desire might be to run .050 so as to not have too great of a gap at .070 (which is starting to push the capability of the ignition system). As the platinum pad retention improved and the plug quality and process control improved over the years the gap could be allowed to creep up.

Based on this answer, I'll definitely keep my new plugs at .060".

Thanks everyone for their contribution to this thread.

One thing is certain, If there is a weak coil, or ignition wire, you will surely find out about it a lot sooner if your plugs are set to .060 instead of .050. moving up .010 is a 20 % increase in the gap that the spark has to jump.

The system may handle it just fine at low to medium RPM & load, but when you try to blow off that 5.0 Mustang, you could be in for a surprise when the firing voltages peak!

Elevated firing voltages cause the high tension insulation to break down sooner. That is the reason that GM decided to lessen the gap to .050 in the first place.

I seriously doubt that you can accurately measure any performance benefits of running a set of .060 gapped plugs over a set of .050 gapped plugs.

It is your vehicle, do with it what you will.

Take Care & Good Luck!

Britt

Britt
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Based on the fact that the plugs are supposed to be set at .060", and I didn't have trouble with them in 149,000 miles, I think they'll be fine. And as indicated, GM didn't specifically lower the gap to .050". The gap was apparently based on the supplier and specifics of the OE plug. In '96, the gap was .050". In '97, it was .060". In '99, it was back at .050". Pretty haphazard if you ask me, and not an indication of any limitation of the ignition system. This car sees full throttle every day I drive it, and it's smoother now than it's ever been.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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I completed a short "how to" page for the spark plugs. My main reason for doing so was to highlight my experience with the two different types of universal joints, and how much easier the job was with an impact gun universal joint.

http://www.jnjhome.net/cadillac/plugs.htm

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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