GM 5.3 owners - MPG and Iridium plug question.

[mjk]

Hello,

First question - for anyone running a 00 + Tahoe/Suburban, what do you typically get for MPG (summer and winter).

Second question - In September, I removed the original Platinum plugs in my 01 Tahoe, and had the replacement Iridium plugs installed. Without doing a 'scientific' MPG study, I knew right away that I lost at least 1 mpg after they were installed. In all the threads I've read, I've never heard this happening. The vast majority of people indicate a slight uptick in MPG and performance with the Iridium plugs installed.

My driving is very consistent, and the winter blend was not online yet, when this downturn in MPG occurred. I didn't do the wires at the time (has 72k on it), and now am wondering if I shouldn't get these installed soon.

What are your thoughts?

 

[Y_K]

Gap?

 

[Brybo86]

I thought Iridium plugs always have a preset and unadjustable gap

 

[147_Grain]

You should ALWAYS verify and double-check the sparkplug gap. Your gap might be too narrow - hence the lower mpg's.

 

[Paulfix]

15-16 combined on my 01 Silverado. Has 187k on it and the mpg has been consistent since new in 01.

 

[Rat407]

Originally Posted By: Paulfix
15-16 combined on my 01 Silverado. Has 187k on it and the mpg has been consistent since new in 01.


Same here on my 02 Silverado and it is a 4x4. I even went with NGK copper plugs and no change in mpg.

 

[mcrn]

I used to own an 03 Yukon that was full time AWD and I would avg 3 to 15 mpgs.

 

[SteveSRT8]

Check the MAF sensor. Cleaning that part routinely was a huge factor in my 05 5.3 Silverado averaging nearly 18 mpg across 125k miles before its recent sale.

Both the TB and MAF are easily cleanable. Also check the PCV as some engines have the orifice style with no valve and they get gummed up easy in colder climates...

 

[mjk]

Thanks for the info. Did check the PCV this summer and it was fine. I actually had the 'rattle can' vs the fixed orifice replacement PCV. In an approximate 3500 mile 1st interval, oil level didn't move at all.

Will be looking into the MAF sensor in the next week!

Originally Posted By: SteveSRT8
Check the MAF sensor. Cleaning that part routinely was a huge factor in my 05 5.3 Silverado averaging nearly 18 mpg across 125k miles before its recent sale.

Both the TB and MAF are easily cleanable. Also check the PCV as some engines have the orifice style with no valve and they get gummed up easy in colder climates...

 

[mjk]

I don't think you are supposed to touch the gap on Iridium plugs....

At least, the vast majority of threads I've read indicated to leave it alone.


With regards to wires, I assume just to stay with AC Delco? And to make sure to check the serial# on the coils for the proper set (GG or HH)?

 

[wirelessF]

GM changed the spark plug gap for iridium spark plugs. They are speced at .040, not the old .060 that is listed in the manual or engine bay. It's in TSB 03D-J-171

http://www.ls1.com/forums/f6/spark-plug-gap-123602/

 

[mjk]

Originally Posted By: wirelessF
GM changed the spark plug gap for iridium spark plugs. They are speced at .040, not the old .060 that is listed in the manual or engine bay. It's in TSB 03D-J-171

http://www.ls1.com/forums/f6/spark-plug-gap-123602/


Yeah, I remember reading that... and that is how they come pre-gapped now.

The .060 gap was how the Platinum plugs were to be installed.

 

[Y_K]

Originally Posted By: Brybo86
I thought Iridium plugs always have a preset and unadjustable gap


True for the 'Performance' series, the ones with the thin electrodes, around or less 0.4mm. The spark is rich there, and it's impossible not to kick the tiny layer of the precious alloy off, unless you work with the ground electrode exclusively.

Double plats seem to be a bit safer and more practical in some applications.

For a Lexus LX I buy exactly the Denso Ir they spec in the manual. For a retired Police Interceptor Autolite Double Plats are more than good enough, in fact, Ford switched to Nickel there later

 

[Merkava_4]

I lost acceleration and fuel mileage when changing to ACDelco iridium plugs.

I'll be switching back to NGK double platinums next time.

 

[wirelessF]

Originally Posted By: mjk
Originally Posted By: wirelessF
GM changed the spark plug gap for iridium spark plugs. They are speced at .040, not the old .060 that is listed in the manual or engine bay. It's in TSB 03D-J-171

http://www.ls1.com/forums/f6/spark-plug-gap-123602/


Yeah, I remember reading that... and that is how they come pre-gapped now.

The .060 gap was how the Platinum plugs were to be installed.


That one post could be relevant to OP's problems:

Originally Posted By: 99RTA
I use 40-45 thous if i want a smooth idle....55-60 if i want more fuel mileage and a little better throttle response.

 

[mjk]

Why I left the gap, as is....

Quote:
Subject: Information on New Spark Plugs and Gapping #03-06-04-060 - (10/24/2003)



Models: 2004 Buick Ranier

2002-2004 Cadillac Escalade, Escalade EXT

2003-2004 Cadillac Escalade ESV

2004 Cadillac CTS-V

1997-2004 Chevrolet Corvette

1998-2002 Chevrolet Camaro

1999-2004 Chevrolet Silverado

2000-2004 Chevrolet Suburban, Tahoe

2002-2004 Chevrolet Avalanche

2003-2004 Chevrolet Express, TrailBlazer

1999-2004 GMC Sierra

2000-2004 GMC Yukon, Yukon XL

2001-2004 GMC Yukon Denali, Yukon XL Denali

2002-2004 GMC Sierra Denali

2003-2004 GMC Envoy XL

1998-2002 Pontiac Firebird

2004 Pontiac GTO

2003-2004 Hummer H2

with 4.8L, 5.3L, 5.7L or 6.0L V-8 Engine (VINs V, P, T, Z, G, S, N, U -- RPOs LR4, LM4, LM7, L59, LS1, LS6, LQ9, LQ4)

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 1.01mm (0.040 inches) when the spark plug is made. 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 gapped should not be used.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

 

[mjk]

Has anyone returned back to the Platinum plugs, after installing Iridiums?

If so, what were your results?


Funny thing was that I could have easily waited until this upcoming spring to do anything. At around 71k on the Platinum plugs, they looked fine (at least for the next 6 months or so).

 

[mjk]

Well, this bulletin is throwing me for a loop; just found another update for older 5.3s.

Feedback?

Quote:
Date: May 21, 2013 Bulletin Number: 13D-070
To: DDG Headquarters and Branches Category: Product
From: Brad Brunken, Product Development Line(s): 41

Subject: ACDelco Spark Plugs 41-110 and 41-962 - Application Update

Description
ACDelco announces that 2006 and older, as well as some 2007, spark plug service applications
covered by the iridium spark plug 41-110 have moved to the platinum plug 41-962. For the
older model years, GM used a double platinum spark plug in production, and these older
applications are to be serviced with the double platinum plug 41-962. 2007 and newer
applications used iridium plugs in production and service requirements will remain assigned to
the iridium plug 41-110. Both plugs meet original equipment specifications for the applications
designated. Catalog changes for the Epicor and WHI systems will be updated in the June
release 2013. ACDelco recommends you begin adjusting your stocking requirements for the
41-962 in preparation of the upcoming catalog updates. The estimated sales volume split
between the two spark plugs is 50/50 based on these application changes and vehicles in your
markets.

 

[mjk]

Hate to bump this, but has anyone else heard about the bulletin I listed above?

I wonder what prompted this move back to Platinum, on the older 5.3 engines?

Feedback is appreciated.

 

[deanm11]

I don't recall what plugs I put in but our 140,000 mile 2002 Tahoe 4wd (never on) gets 15 Suburban driving, 18 ~68mph highway like clockwork its whole life. Maybe a smidge lower with winter gas and slightly better rest of the year. I keep the tires inflated slightly high to spec and have always run a K&N filter kit.