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Discussion Starter #1
I've been seeing some guys talking bout setting the gap of the plugs in a vortec down to 0.40 instead of 0.60, mine are at 0.60 and it runs good but if dropping it down to 0.40 will help it out I will do it but I aint found a straight answer on it really so lets get some feedback on this cause Its stuck in my head. Thanks
 

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Gapping them at .060 will give you a better spark & fire the mixture better & with gas approaching $4.00 a gallon this is where I'd leave them. Gapping them down to .040 only gains you if your coil is weak, or your wires are marginal because a .040 gap is easier to jump. Also some lazy types set them at .040 because as the gap erodes after millions of fireings they don't have to R&I the plugs & regap them. They just erode from a .040 gap to the .060 or beyond & by the time the gaps are getting too wide, it's time to replace them anyway so they never have to R&I the plugs except to replace them.
 

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Mike Heartbeat just sent me an email with a link that tells why you DON'T change plug gaps on iridium or platinum plugs. He said the iridiums are gapped at .040 & the platinums are gapped at .060 & you should not try and change them. Mike knows a lot about this stuff so I would follow his advice. Since yours have the .060 gaps I'm guessing you have the AC Delco platinums, so if you have the platinums gapped at .060 leave them there. Here is Mikes' link.
http://www.gmtruckclub.com/forum/sho...=Damaged+Plugs
 

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Discussion Starter #4
The Plugs I just put in the truck are Iridium AC's and they were gapped 0.60 out the box and I checked to make sure they were and it said Iridium plugs on the side of the box and the truck runs pretty good.
 

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Leave them at 0.60.
 

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The Plugs I just put in the truck are Iridium AC's and they were gapped 0.60 out the box and I checked to make sure they were and it said Iridium plugs on the side of the box and the truck runs pretty good.
If they are iridiums & are gapped at .060 then you are stuck between a rock & a hard spot because they are suppose to be gapped at .040 as per GM, & you can't regap them from .060 to .040 as per GM. Here is the GM tech bulletin. If you haven't installed them yet I would take them back & get a set that are gapped properly to .040

This bulletin is being revised to bring attention to the Set Gap Per Vehicle Specification on the ACDelco® Iridium Spark Plug Boxes. Please discard Corporate Bulletin Number 03-06-04-060 (Section 06 -- Engine/Propulsion System).

• A new spark plug has been released for use in the above vehicles. The new spark plug has an Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the spark plug has also changed.
• The new spark plug, P/N 12571164 with AC Delco P/N 41-985, is gapped to 1.01 mm (0.040 in) when the spark plug is made.
Notice: The spark plug gap is set during manufacturing and should not be changed or damage to the spark plug may result. Any new spark plug found to not be properly gaped should not be used.
 

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.040" regardless of the composition of the plug (copper, platinum, iridium). It's nothing to do with laziness, and the bigger gap will not produce any economy/performance benefits. Rather, the occasional misfires will result in poor driveability and impact economy. Furthermore, tightening the gaps will greatly reduce the load on the entire ignition system resulting in longer component life. The energy required to spark a .060 gap vs .040 is about six times more.

These engines run so lean that a big gap is not required to avoid plug fouling.

As for the Iridium at .040 vs platinum at .060, GM is conveniently using a new plug coating to bury a long standing problem. The coating on the plug does not change the physics of sparking a gap in the intense pressure of the combustion chamber. By recommending the Iridium with the .040 gap, they increase customer satisfaction with the improved driveability resulting from the tighter gaps.

As for my personal experience....I was running Bosch +4 in my 97 K2500 w/350 at 140K. If you look closely at the +4 plugs, you will see the gaps are huge. The truck was very poorly. Low power, sloppy idle, quick to overheat, and unstoppable pinging/spark knock. I figured I was in for some major engine work, if not a new long block. At the advice of a friend, I put in the AC Delco Platinums gapped at .040. I was very skeptical that there would be any change at all. Much to my surprise, it felt like a new truck. All the symptoms I listed immediately disappeared, and economy improved.

As for gapping plugs, it's OK to adjust the gaps on Platinums, which is why I run them when available.
 

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Discussion Starter #8
Well I know my truck still is getting **** gas mileage and thats after a full tune up, oil change, and fuel filter and bottle of lucas injector cleaner and im just running 16x8 M/T's and 265/75 Mud tires so it should be getting better than what its doin I can drive 30 miles and there goes a 1/4 tank I know it a 350 and a big truck but my 2000 Silverado got 18/20 mpg and I know these vortecs get good mileage so my question is if I get a set of Platium Plugs and take them down to 0.40 would the truck get some better mileage??
 

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Well I know my truck still is getting **** gas mileage and thats after a full tune up, oil change, and fuel filter and bottle of lucas injector cleaner and im just running 16x8 M/T's and 265/75 Mud tires so it should be getting better than what its doin I can drive 30 miles and there goes a 1/4 tank I know it a 350 and a big truck but my 2000 Silverado got 18/20 mpg and I know these vortecs get good mileage so my question is if I get a set of Platium Plugs and take them down to 0.40 would the truck get some better mileage??
You want the..... A/C Delco iridium spark plugs are the latest evolution in high performance plugs. The natural properties of iridium, with a melting point of approximately 700 degrees Celsius higher than platinum, help enable the plug to burn fuel more efficiently and to deliver better performance. As a result, the iridium plugs have a minimum service life of 100,000 miles (service life varies with individual driving conditions.)

These are the Plugs I'm running in my Truck......and It Runs Great!!

ACDelco 41-985 - ACDelco Iridium Spark Plugs

large image $6.95

  • Spark Plug, AC Delco, Iridium, Resistor, Each


---------- Post added at 01:30 PM ---------- Previous post was at 01:21 PM ----------

Edit:......By the Way.....What year is your Truck??

---------- Post added at 01:31 PM ---------- Previous post was at 01:30 PM ----------


 

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Discussion Starter #10
Its a 98 K1500 Ext Cab with 5 speed, and I'm gonna check on getting them plugs 99'heartbeat but I was looking around and seen some guys have gotten poor mileage from the thermostat and mine will run up to bout 210 then after that it'll drop to 160 and does this the entire time I drive up and down could that be a issue with it not stay at a constant temp I know I changed the one out in my moms sunbird it was doing the same now it runs alot better and gets amazing mileage.
 

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Its a 98 K1500 Ext Cab with 5 speed, and I'm gonna check on getting them plugs 99'heartbeat but I was looking around and seen some guys have gotten poor mileage from the thermostat and mine will run up to bout 210 then after that it'll drop to 160 and does this the entire time I drive up and down could that be a issue with it not stay at a constant temp I know I changed the one out in my moms sunbird it was doing the same now it runs alot better and gets amazing mileage.
Now that I see that your Truck is a 1998" with the 5.7 liter 350......you will not be able to get the A/C Delco Iridium plugs as they are for the 1999" and up NBS Trucks and SUV's.....Your Truck being a 98"....the A/C Delco Plugs you would be looking at are the ones below,


SPARK PLUG ASM
Part Number: 12
Product Notes:
[Rapidfire Spark Plug]; Reg cab ; .060 GAP

Per Vehicle: 8; Years: 1996-1998






SPARK PLUG ASM
Part Number: 41-993
Product Notes:
[Platinum Spark Plug]; .060 GAP

Per Vehicle: 8; Years: 1996-1998
 

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So sorta kinda off topic but still on the AC Delco plugs. When I changed them out on my truck and put new AC Delco iridiums in I noticed (either the stock AC Declo or new ones, I dont remember) that on one side of the plug it said AC Delco and on the other side it said NGK. the only reason I say this is because in the post referenced by stephen a poster complained about the NGK's then went to AC. Has anyone else seen this? Are they made by the same people? I use NGK in the imports I have had (nissan, toyota, etc) and AC delco in my truck and now the new commuter (Saturn. .040 was the gap on those too for the rapid fires). I guess I will look to see which set of plugs it was on. the new plugs were pregapped at .040 and said not to adjust.
 

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Discussion Starter #13
Would my thermostat be causing poor gas mileage after the truck warms up and will driving the temp gauge is up and down the entire time between 160 to 210 and I've also noticed in the mornings it will leak alittle anti-freeze but after it warms up it stop and wont do it again till the next morning and I see were it leaks right at the bottom of the radiator support on the driver side but looking under the hood I cant see were it comes from any thoughts?
 

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I have 2002 silverado with 5.3 litre. Code P0300 and P0327 keep appearing. Whenever I clear the code it takes another 2 days for the engine light to come back on (not flashing). I just found that my plugs, ACDelco #41-961 are gapped at .039. For this truck irridiums should be at .040 and platinums should be at .060 from what I have read. So, are my plugs mis-gapped? You no longer just go be the manufacturer gap specs?
 

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Well I know my truck still is getting **** gas mileage and thats after a full tune up, oil change, and fuel filter and bottle of lucas injector cleaner and im just running 16x8 M/T's and 265/75 Mud tires so it should be getting better than what its doin I can drive 30 miles and there goes a 1/4 trank I know it a 350 and a big truck but my 2000 Silverado got 18/20 mpg and I know these vortecs get good mileage so my question is if I get a set of Platium Plugs and take them down to 0.40 would the truck get some better mileage??
 
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