5.0 - Sluggish & Pinging Under Load..What Should I Check?

[Thallarsen]

Although I’ve got a good idle, and a smooth running engine, my ‘99 Limited is sluggish going up hills at highway speed, and I’m noticing an increase in pinging under light loads at speeds above 45/50 mph.
My mileage isn’t too bad, and I’m using major brand regular gas. I’m not getting bucking or rough running under heavy acceleration....something that fuel starvation would cause - just lack of power at highway speeds & pinging under load.
New Autolite plugs, Taylor Spiro wires, new fuel filter, MAF is clean, and the air filter isn’t too bad.
I’m not hearing a vacuum leak, but I can’t figure out what else to check.
Seems like either vacuum, or a timing advance issue.
What should I check?

 

[Lemondrop]

How many miles your injectors have ?
My 96 is pinging when I stomp the pedal down pretty bad . It's on my to-do list .
The engine has 158,000 on it so I figure my injectors are giving it up a little . I did notice a whine coming from the engine compartment . Dunno if I got a vacuum leak , belt noise , or tranny making noise . Works fine other than ping at upper rpm's or full throttle romps .

 

[Thallarsen]

128k on the truck. Mostly highway miles. I've taken out the MAF again, and thoroughly cleaned it; and will reset the PCM and see what it gets me.
The jury's still out on whether Sea Foam works; at least from what I can gather. I'm reading some posts praising it, and some saying to stay away from it.
What puzzles me, is that my mileage has been really good for an AWD V8 SUV. Consistent 18 to 19 mpg (75% highway.) Now it's more like 17, but that's still pretty good. It's just so sluggish going up inclines at high speed.
My 250k '91 had more higher acceleration punch, but the mileage was never as good......go figure.

 

[james t]

sounds like carbon knock. Seafoam (or water) will do the trick. just make sure its done correctly, or you could hydrolock the motor.

 

[TheJMan]

Try using some kind of fuel system cleaner. Some people swear by Techron, but I used Valvoline complete fuel system cleaner and it really helped smooth out the engine. I haven't had too many problems with pinging, but my MPG went up slightly after using the Valvoline. I highly recommend it.