I just finished the plenum gasket fix, replaced the o2 sensor and water pump on my '01 5.9 Ram. Took it for a ride and it still detonates around 3000 rpm under acceleration. I thought the new plenum gasket would fix all that. Any thoughts on why this might be happening?

 

Did you run a can of SeaFoam through the intake before you changed the plenum gasket? Also, did you put in a new gasket or a new plate/gasket/bolts?

 

What about the cat? If the plenum was blown it's probably clogged pretty good. And do you have a PCM flash sticker under the hood some where?

 

hmmmm mine still pings too.... could be cracked heads between the valves, i suppose. leak down test, or a compresson test could solve that mystery. check the cat first, like zman said, then go from there. if you have the death flash, get it re-tuned by an sct tuner, or the like..

 

BTW, since no one mentioned it, to check if the CAT is clogged or not...simply unscrew the pre-CAT O2 sensor. If it runs noticeably better with the sensor removed then the CAT is restricting the flow of exhaust.

If there is little to no difference then it is likely not your problem.

 

+1... I should have mentioned that. Sorry

 

Fixing the plenum gasket leak will prevent oil from leaking in. There is still plenty of buildup from the original leak which is actually the cause of the spark knock. The carbon buildup can't dissipate cylinder heat and you get the detonation. If you haven't yet, you will need to run a can of sea foam through the system. Directions on the bottle say to let 1/2 the bottle suck up through the brake booster vacuum line till the engine cuts off. Then let it sit an hour. Crank it and after the smoke clears then replace the plugs.

 

autolight 3923 plugs helped my problems also timing chain could be stretched to the max


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I did the seafoam trick (neighbors didn't like me much that day and just changed the plugs. #8 looked fine. The truck has 175000 miles on it and the original cat. I'll try running w/o the o2 sensor and see what happens. I kinda thought I should have replaced the timing chain while I was into the water pump, but didn't want to open it up. Thanks for the wisdom fellas.

 

Forgot to mention, I got the plenum plate kit from Hughes. I thought it was a great deal. And I have not found a pcm flash sticker anywhere.