Hey guys, I just picked up a 2001 Ram 1500 with the 5.2 for towing my boat. My issue is it gets terrible gas mileage. The boat and trailer are about 5000lbs and I consistently get 6mpg, the truck also has a very hard time keeping it over 60mph. I did the magnet check and it stuck to the bottom of the plenum, there was also oil on the bottom. The truck doesnt seem to run rough but when I floor it does make a really strange griding/vibrating noise. It seems to have good acceleration by itself but when I pull the boat its terrible. Im getting the p0455 code but thats not related to this. It also doesnt idle rough. Is the magnet check and the poor mileage a definite indicator of plenum failure?

 

Do not tow in overdrive. That will smoke you trans in pretty short order.

What kind of gas mileage do you get when NOT towing? If you are still in single digits, then yeah, something ain't quite right there.

Last time the truck had a tuneup? How's the air filter look? Did you see anything toward the back of the inside of the intake? How many miles on it?

The code may indicate you have a bad hose in the evap system somewhere, which could be causing a vacuum leak. Inspect the system, (all of it) see if anything obvious presents itself. Still have the stock gas cap on it? How's the seal on that look?

Welcome to DF!

 

I always turn off the O/D when I tow. The truck has 194k miles on it. Ill see if I can get a better look at the back of the intake. Theres def a vac leak somewhere, the a/c blows half on the floor/half vent and when I give it some gas itll switch to only the floor until i let off then goes back to vent/floor. I just have no idea where to begin to look for the leak. The check valve mentioned in the wild vents thread is good to go. Most likely the stock gas cap. It also smells like its dumping fuel at idle, but could be an exhaust leak. Not sure about a tune up.

 

Most people when they change the plenum they just replace the gasket not the plate. Best thing to do is pull the throttle body. Get a mechanics mirror (harbor freight sells one with a light for $8) and look all over the plenum.

 

You need to start with a tuneup. Plugs, wires, cap, rotor, oil/filter change - check the air filter. Achieve a baseline of foundation so the engine has the opportunity to run correctly. If its been five years since you did a tune up, its just going to run better anyway. Then check for a vacuum leak and fix any that you find. Look for weathered vacuum lines. Any vacuum leak causes the PCM to act inappropriately as does any temp sensing and/or cooling thermostat. You should not smell fuel ever -- so find out where the fuel smell is coming from and fix the problem back to the factory design/intent. Thinking you have a bad plenum is miles away in the journey of troubleshooting bad gas mileage.

 

Copper plugs not platinum or iridium. I like NGK plugs. Do what ^^^^^^^ he said, and maybe new NTK O2 sensors.

 

Thanks guys, ill try the tune up and report back.