Hello all, I have a 98 Ram 1500 with 178K on it. A while back I started getting a loud spark knock and the check engine light would come on when I was at highway speeds, usually just trying to settle around 75 and stay there. If I gave it more gas or slowed down it would stop. I have changed the plugs, wires, rotor cap and rotor button. After all that it still did it. So I just recently changed all 8 fuel injectors. Now it is much much better but it still does it just a little bit, the check engine light will just flash at me now. Whats left to change? Like I said above other than on the highway this truck runs great.
Thanks.

 

Check the plenum gasket. Look down the throttle body, and see what you see.

 

+1 the plenum is shot....you will need a kit from hughes or APS Precision, replacing the gasket will not fix the problem.

 

I had the same problem. check the TSB for your plug wire routing. if any of the wires are to close to eachother they will cross fire. i relocated all of my wires so none of them were touching, reset the computer and nomore spark knock of engine light. Takes about 15 mins and a bag of zip ties. try it you might be surprised.

 

The plenum for sure, along with clogged cat,bad pre cat o2. Don't wait long to check theses items, the extra heat from a clogged or almost clogged cat will result in a cracked head.

 

While you're in there checking things, don't forget the PCV valve.