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About GMTfour100

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  1. Indeed that’s what I’ve always heard to, until I read maintenance specs of replacing coils every 100k miles, which lead me down a road of different coil types. The real question here (regardless of whether coils need replacement prior to failure) is whether the “newer design” round D585 coils improve performance and/or gas mileage, compared to the square D581 coils. Hopefully someone who knows will chime in.
  2. Ahh okay thanks. I thought I read somewhere that ignition coils should be replaced every 100k miles. My truck has 150k miles in original coil packs. So if they are working, they don’t need to be replaced? And they’re firing just as well as brand new ones?
  3. Bump... Nobody here knows the differences between these two coil pack types? ..Really?
  4. Doing a tune up on a 2001 Yukon XL. Is it possible to swap round coils into a truck that came with the square ones? My 2001 Yukon XL came with the square coils (D581), however, I understand that the newer design coils (D585) are a bit "hotter" and began getting installed into Chevy/GMC trucks in 2003 (which is why many people swap them into LS motors). O'Reilly Auto, Amazon, Ebay, etc.. all state that both types of coils will fit my truck (00-02 GMC/Chevy). I know that the round (D585) coils will require slightly longer plug wires [9748GG vs the 9748HH for the square (D581) coils]. Does anyone know if I can just swap these into my truck or will I need a different mounting bracket for each side of the motor? (part 10457736). Thanks in advance to anyone who chimes in.
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