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Round vs square ignition coils??

GMTfour100
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GMTfour100 Enthusiast

GMTfour100

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Posted (edited)

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. 

 

 

 

Edited by GMTfour100
GMTfour100 Enthusiast

GMTfour100

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Posted

Bump...

 

Nobody here knows the differences between these two coil pack types?

 

..Really?

 

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

I do know that the dwell settings for the coils are different in the calibration.

 

If you are asking me here, it's not worth changing them. I've worked on many LS engines in the past and I've rarely ever ran into a coil issue. If they work now, they should be just fine.

C/K Man Enthusiast

C/K Man

Posted
Posted

The round coils are made by Delphi, the square ones are made by Mitsubishi Electric (even though they are stamped 'AC Delco').  The round ones are supposed to be 'better', but don't ask me why!  It seems to be random as to which trucks get what coils, and I have always replaced kind for kind.  I agree they don't go bad very often.  Usually if one does go bad, it's #8 because a bad heater hose fitting leaked Dexcool all over it. 

GMTfour100 Enthusiast

GMTfour100

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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?

 

 

GMTfour100 Enthusiast

GMTfour100

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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.

 

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

There will be zero difference in performance or fuel mileage if just changing them out for the hell of it.

 

Only if there was a problem with them would replacing them bring it back to what it was like before an issue.

 

I've watched people spend $500+ on "performance" coil packs for LS engines, 3800's and others only to gain nothing but a lighter wallet. Half the time these new coils would be bunk out of the box or die within a year. Then they look at the guy with 300k miles still running his 17 year old coils without a single issue.

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  • 1 month later...
Dev_the_dude209 New Member

Dev_the_dude209

Posted
Posted

If you swap over to the round coils you will also have to swap out the rails that hold them to the Valve covers! I did this swap on my 5.3 lit 2001 Silverado. Runs great and looks a lot cleaner, performance style gave my truck a little more pep. Better than the stock Square ones!

Dev_the_dude209 New Member

Dev_the_dude209

Posted
Posted

If you swap over to the round coils you will also have to swap out the rails that hold them to the Valve covers! I did this swap on my 5.3 lit 2001 Silverado. Runs great and looks a lot cleaner, performance style gave my truck a little more pep. Better than the stock Square ones!

  • 3 years later...
Jollycats Photography New Member

Jollycats Photography

Posted
Posted
On 7/16/2020 at 7:00 PM, Dev_the_dude209 said:

If you swap over to the round coils you will also have to swap out the rails that hold them to the Valve covers! I did this swap on my 5.3 lit 2001 Silverado. Runs great and looks a lot cleaner, performance style gave my truck a little more pep. Better than the stock Square ones!

I appreciate this information so much! I have just become the new owner of a 2001 Suburban (Bernice, 300k, still sassy) and I was really stuck on this coil thing trying to buy parts. I'm planning to replace all 8 when I do (or help with/have done) the plugs and wires in a few w

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