I have a 99 1500 5.9 Gas that no matter what i do it will not stop knocking underload. it does not matter what gas i run it still knocks. I have checked my plugs, put new ones in and gapped them corectly( according to MSD) and the damn thing still knocks. i'm running the stock coil, MSD6A, and one stage colder plugs. Also the Cat looks brand new, i mean very shinny very pretty. is there anything else i'm missing?

 

plenum gasket..

 

Check the crankshaft position sensor?

 

I can't see any of the tell tale signs that the gasket is bad. the other thing is that the engine surges sometimes. maybe two or three hundred RPM's. it also seems to not want to stay in any certin gear. it's almost like the engine is not putting out all it has. Plenum Gasket? Oh yeah i get about 6 mpg, i'm not kidding.

 

Take some carb cleaner, or brake clean and spray around the gasket areas on the intake, if the rpm rises you know you got a leak.

 

No leak on the outside must be something else. Oh yeah got to love the WHL. Love the Tips!!!

 

I thought I'd mention installing a 180 degree thermostat, if you haven't already. I seen your running colder plugs but you I didn't notice if your running a 180 thermostat.

Try searching the crankshaft position sensor that Rom had mentioned. There's some threads on modifying it to in effect advance your timing, which since your already knocking you don't want to do. It should work in reverse and you would be able to mod it to retard your timing a touch and possibly stop your knocking under load. This should probably be your last option once you've run out of other options.

Ok, make it your second last option. The last option is a re-flash of your PCM at the dealer commonly refered to here as the death flash. Your truck won't knock, but you'll definitely not be happy with the performance of your truck after.

 

check your iac and tps. i dont know if that will cause knocking but it was what was causing my truck to surge

 

take off the TB and look down to the bottom of the intake manifold. Look for oil pooling in any corner or the sides... if you have oil pooling, your plenum is leaking. 6 mpg also indicates a possible plenum leak... both are tied together with a blown plenum gasket.

lastly, once your plenum is sealed, cap & rotor. the msd will eat thru them like butter... I was replacing mine every 15~20k and was trying to chase down a pinging issue for about 1000 miles before I figured it out.

 

So Steve should i just ditch my MSD? or get used to replcacing the cap and rotor? The Tstat is high on my list along with the plenum gasket. I just don't have a place to do the work on the truck. Thanks for everyones help.