Having problems with your 1999 GMC Yukon ?
1999 yukon spark plug diagram - 1999 GMC Yukon
Answers :
Firing order 1-8-4-3-6-5-7-2. looking from front of vehicle driver-side front to rear 1-3-5-7 passenger-side 2-4-6-8. hope this helps Tim 
Repair Help & Product Troubleshooting for 1999 GMC Yukon
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