Sorry, this first post is a bit wordy, but I need to explain the situation.
So our family wagon is a 2001 Chevy Suburban 2500 4x4 with the 6.0L engine that we have had now for around 4 years. The previous owner had installed some Edelbrock Headers. He also had the ECM reprogrammed for economy and towing. I'm not sure how that is possible, but he said you get one or the other, not both at the same time. He said when towing just put your foot into it when climbing a hill and the vehicle will pull hard. Otherwise, just normal driving will produce the economy. His acid test was the commute his wife made with it everyday to work. Before the mods they were filling the tank every 5 work days, after the mods they were filling every 7 to 8 work days. Not bad.
Anyways, I have found that when driving up a grade at speed, especially with the whole family aboard, the engine would ping a little. Typically I would back off the throttle or cause it to downshift to eliminate that. I always suspected the econo tune was the culprit.
So a few weeks ago we needed to make a trip to the coast from the interior. I decided it was a good time to replace the spark plugs and air filter before our trip, I had never touched them since we bought it and it had a bit of a rough idle and hesitation as of late. I also did a Seafoam treatment of the upper intake to clean things up before I changed the plugs. The plugs that came out were the NGK TR55 plugs that have a factory setting of .050" gap. As far as I know, these plugs were never recommended for this engine. The plugs looked good with a clean burn. I checked the gap on the old plugs and they seemed to be anywhere from .061" to .065" gap. I checked the manual and it said to use .060" gap. I have since learned that GM has updated their recommendation to a plug with .040" gap. I went to Lordco and their computer suggested using NGK TR5GP, a platinum plug with .040" gap. I bought them and installed them. On our trip to the coast, as we passed through Kamloops by climbing the steep hill out of town, the engine pinged very badly like I had never heard before and even caused the check engine light to come on (knock sensor code). I pulled into Canadian Tire and bought a few bottles of octane booster, one for the way down and one for the way back. No more pinging during that trip.
I have since filled up with regular gas a few times since the trip and notice some pinging when the engine labors up a hill. It is certainly more pronounced now then from before I changed the plugs. The rough idle and hesitation is gone too, but the pinging is not good. I cleared the engine code but it has since returned, even when the engine is NOT pinging.
Not sure what to do. I am considering opening up the gap to .050" and see what happens. I understand that too small of a gap will result in an incomplete burn. Anyone else have similar issues? Did you find an solution to the problem?