Okay,

Two weeks ago I started having a pinging issue on all but the lightest acceleration. I thought maybe it was cheap gas I got a Sam's Club so I bought a bottle of octane booster and it went away. I refueled at my trusty Quiktrip that I had been going to for the last 4 years and the pinging returned. I've never had a problem with this station's gas, so I think "Maybe that damn plenum gasket's blown again." Yesterday I pulled the TB and the inside of the keg was a clean as could be.

What the heck's going on here? Nothing else has changed that I'm aware of. Is there anything that sounds similar to pinging that I might be misdiagnosing?

 

You don't have Autolite plugs do you? If so I'd replace them with Champions and see how if it helps. Are you running a programmer?

 

I'm running the NGK V power plugs, but I've had those in there for months.

The SCT tuner hasn't changed settings either. I haven't done a thing to the truck recently, as I've been trying to save up for the head & cam swap.

 

pinging = predetonation.
causes:
1. timing too far advanced (firing too much before TDC)
2. cylinder too hot
carbon buildup holding heat.
fuel too lean, from computer or vac leak.
3. fuel octane too low.

check for other vac leaks, maybe a booster hose or something.
you mentioned a stumble, possible vac leak maybe that's gotten worse ? you could try to temporarily plug off as many vac's as possible

could the 02 sensor be telling the computer to lean out too much ?

fuel - you covered that, but - could QT have changed their gas. maybe try another place, brand name, etc..
carbon - try seafoam or mopar cc cleaner.
timing - i know you don't want to remove SCT, but could you temporarily remove it

 

I bought a bottle of octane booster just to be sure it is pinging, but it sure sounds like it. Hopefully after it mixes in the gas overnight I'll know for certain. I'll also restore the stock tune which should be well retarded of the SCT flash. If that fixes it I'll at least know and talk to Sean about pulling a little more timing out. That's not the route I want to go, as detuning it isn't much better than what Dodge did.
I did run some MCCC last week thinking it might be carbon, but that didn't fix it.
Ambient outdoor temps have been cooler recently, the coolant temp gauge hasn't budged off of halfway between 140* and 210* in over a week.

I'll have to trace down the vac hoses this weekend. But I would have thought I'd hit the ac vent through the defrost problem before I hit a pinging problem.

Would it be possible that there was enough bad Sam's Club gas left in the tank to "water down" the QT gas octane? I did add Octane booster to the Sam's gas, but my understanding of octane boosters is that they don't alter the gasoline, so I could have "watered" it down as well. Maybe?

 

i image that the sct advance is contributing to the problem, but, its been fine up until now, right? so don't reprogram back to stock until its a last resort. and certainly don't change the sct tune either.

i don't know much about octane booster. i suppose its possible that the QT gas is borderline and the sam's is so low in octane, that there's not enough boost for the whole mix. an easy way to find out is to dump in another can of boost.

here's another ugly thought. i wonder what was in the sam's gas ? if it was something other than gas, it wouldn't be the first time that a tank got filled up with diesel or heating oil or kerosene or who know's what.

i filled up my old chevy with diesel fuel one time and it ran sort of sluggish. i can't remember if it pinged or not...

 

Yea, that's what's bothering me. Damn Sam's Club. I should have known better. I'll have to grandpa it until I can get the tank down to about empty before I fill up again.

 

I've been having this problem lately, actually my mechanic and I are diving into it tomorrow. Could cracked cylinder heads have anything to do with the pinging? I have same stumble and its driving me nuts right now.

 

Squirrels, you may want to try a tank of the Chevron high-test and see what that does. I'm thinking it's just bad gas you're dealing with.