My tuck is 2014 GMC Sierra 1500 6.2 with 55,000miles have had afm turned off with tuner since 6000miles. I have always ran 93 from top tier then about 3 months ago started getting sam's club 93 gas and then for first time filled up with Sams 87.
The day after put in the Sams 87 I changed my oil, changed my serpentine belt and both stretch belts and I had to turn the crank pully to put on the stretch belts. Finally I removed throttle body and cleaned it. Also clean MAF sensor. The first start up after all this sounded horrible like it struggled to start for few seconds but then started and ran normal.
Then that week driving it bogged down 2 or 3 times. Then that weekend I did a full throttle acceleration and had a CEL for misfire cyl 7 and traction control light come on and lost power and truck was chugging. Next day swapped coil packs with another and cleared code. It ran fine that day and drove 50 miles and I was at half tank so filled up with BP 93 and added octane booster. A couple days later CEL for cyl 7 and tract control light again when accelerated hard. Next I changed plugs/wires and it drove fine for 4 days and even with hard full throttle accelerations no issues. Then 4 days later accelerated hard and CEL came on but only flashing but no traction control light but it didn't drive any different and no loss of power. CEL flashed for about 20-30 sec and went off. It was Cyl 7 misfire again. I brought it in to shop 5 days later and he tested Fuel injectors with scan tool and drove it reading data for misfires and fuel pressure. He floored it a bunch of times and had no CEL and injectors were all ok. He said he has had failed AFM lifters before with Cyl 7 misfire CEL but he said mine is not driving or sounding like any of the ones he has seen.
He said there is a bulletin for upper fuel system cleaning with cyl misfires but the dealer would have to do it as he didn't have the machine. He thinks it is bad gas or a gummed up intake valve and it is coaked up with carbon.
Would a bad tank of gas cause these issues I am having or could turning crank pulley to put the stretch belts on the ac compressor and vacuum pump done something.
Anymore suggestions? Should I use up the half tank I have then refill with top tier and a fuel cleaner?
I have always ran 93 f
waste of money
have had afm turned off with tuner
did you try un-tuning it?
CEL for cyl 7 and tract control light
If the traction control light is on, then there should be trouble codes other than misfire. Need a good scanner for that.
See the misfire section in the FAQ for more troubleshooting
My truck has a 6.2 which strongly recommends 91-93 in the manual but can run of 87-91 but says to switch back to 91 if any knocking occurs. The traction Control light with check engine is the limp mode I guess. The only code ever coming up is cyl 7 misfire. I guess I could try turning afm back on and dry a little to see what happens.
My bad. I didn't realise the 6.2 was a high compression engine.
Is it a flex fuel engine?
What do the fuel trims say?
No it isn’t flex fuel. Im an not sure what fuel trims are I will have to check but the shop I just went to today said everything fuel wise was normal when he checked and drove it. He thinks it needs upper engine carbon cleaning which is possible based i. The GM Tsb for what I have going on. Valve may be sticking and its a GDI engine and I do all short trips 3-5 miles around town
I agree that's a likely possibility.
Why did you turn the crankshaft pulley instead of using the tensioner pulley?
The tensioner pulley is for the serpentine belt. The AC compressor and vaccuum pump each have there own stretch belt that runs of the crank pulley with no tensioner.
There has to be some way, like a slot on the alternator, to adjust the belt tension.
no doc, they are stretch-to-fit belts.
Wow - sounds like another money saving feature. Thanks @mmj.
They seem to work well doc. No tensioners to wear out.