My 1999 Ram 1500 (Magnum 5.2L) 4x4 is showing blown plenum symptoms listed in the End-All Be-All Plenum thread.

• Chugging with unusual acceleration and shifting patterns
• Refuses to go past 60mph
• Slow to climb hills
• Acceleration and shifting mostly normal when the front O2 sensor is out (meaning probably clogged cat)
• 7.5mpg vs 11 originally
• Magnetic on extendable magnet (probably OEM plate)

I'll bet my #8 spark plug is going to foul soon.

Here are pictures through the throttle body; the oil you can see is a very thin sheen and not much is burnt up. I think it might've been replaced as it's really clean except for the oil coating. Does it look blown enough to clog my cat?

There is no oil coming out of the PCV valve either, but I ordered a new one as the truck is new to me as of 7000 miles ago and I dont know how old the current one is.

If it's blown, I'm going to get this plenum rebuild kit. Does it have everything I need?

 

Yep, yours is blown. And yep, that kit will have all you need to fix the plenum.

While the intake is out of the way, is a golden opportunity to change the cap/rotor/wires as well. If you don't know how old the plugs are, change those too. Standard copper plugs in the brand of your choice please. Skip the rare-earth fellers, these engines don't like 'em.

May wanna pressure test your cat, and see if it is clogged. Any decent exhaust shop should be able to do that for you.

 

Gotcha, thanks. I already replaced the plugs but I'll replace the cap, rotor, and wireset too. I'll have a shop check the exhaust beforehand probably.

I really appreciate your quick answer and supporting information. Have a great day.

 

Will you are in there with the intake off I would replace the cam sensor in the distributor and maybe the crank sensor aswell. Cheap insurance on these old trucks. PITA to get back there when the intake is on. My two cents. You could also just hook a vacuum gauge after you fix intake problem to see if you got good vacuum. If so that rules out bad cat.

 

Another good thing to do is to remove and clean the intake air temp sensor. It gets coated in oil n thus sends the rong air temp to the computer, causing lack of power problems as well.

 

Thanks guys, I'll take care of those too. I appreciate you taking the time to help me out.