Last night while towing a 20ft enclosed trailer with my truck i heard it starting to ping when i got to the 2,800-3,000rpm range when i back off a little i didn't hear anything it was just around that RPM range. i also towed in the tow mode in 3rd gear. My truck is a 4.8L 2001 GMC, i've up graded to AEM air intake, JBA headers, 3in flomaster exhust,from the cats back on back, 4.56 gears on 35's . no check engine light came on or anything. any thought's or suggetions to what would cause this ? the truck does have a 130,000 miles on it, mostly freeway.

thanks,

 

maybe bad gas or some kind of valvetrain/exhaust noise. trying running some chevron 93 for a tank.

 

Might be time for some seafoam or top end cleaner. The build up can often increase the CR past 87 octane usage.

 

+1 Try cleaning the induction system/combustion chambers with some Seafoam, with 130K you may have alot of carbon build up that will cause hot spots which lead to detonation. If you search "seafoam" you will find some info about the product. I usually clean the throttle body at the same time that I do an induction service. Basically you want to use a vacuum line such as the brake booster hose to slowly suck 1/2 to 3/4 of a can of Seafoam into the intake (engine must be in operating temp first). Then let the stuff soak in for about 15-20 min (I think the can says 1/2 can for 5 min, but I like to use a little extra and let it go a little longer). Then start it up and get ready for the smoke show!! Beat the **** out of it for a bit and you should be good to go.

If this service doesn't help, you may have to look for a lean condition, EGR issue, vacuum leak etc. Might be worth it to use premium gas while your'e towing if necessary.

 

sounds like bad gas to me.

 

What octane do you run currently?

 

i did forget to mention i have a hyperhand held tune in if for the 87 octane, but i run 91 from different chevron's and 76 station out her in california, i was thinking of maybe changeing out the fuel filter thinking its' partial clogged and the motor isn't getting all the fuel it's suppose to, i just changed my fuel pump last month so i know it's not that.

thanks again

 

that would be a good idea. check the plugs and sea foam it while your at it just to be sure it's nice and clean.

 

You need a real tune to compliment the exhaust.

 

Ever replaced your knock sensors? The back sensor is prone to rust/corrosion due to a chitty design where the hole it sits in is like a big funnel for water. When it happens the knock sensor doesn't make a connection and if it starts knocking it doesn't send the signal to retard the timing as needed. IIRC it turns on a check engine light but with that hyperpoo on there its hard to say.