I think a bad cat would get spotted by the O2 that follows it and it would switch on the check engine light. I was told that that particular O2 is responsible for comparing values with the O2 ahead of the cat to make sure the cat is doing its job. As far as power goes i find the truck a little lazy for that big of a motor and what i hear about them. My previous truck was a 1997 Chevy 1500 longbox reg cab 4.3L 6 cyl and it wouldn't get left in the dust exactly by this one if you know what i mean. Not by much anyhow. I still have the original sheet that came with the truck and all the options and specs from the first owner.It came with the truck manual and it states i should be getting 14mpg-city and 20mpg-highway. I barely get close to 14mpg-highway. When I told a mechanic about what the sheet was claiming they said: "Yeah, maybe brand new but the truck is almost six years old." The Chevy was 10 years old 2 months ago and was still getting the mileage that GM claimed in 1997. I hope i dont have to sell this truck for something else even a diesel i would loose too much money, but i guess thats what i get for buying a vehicle without doing my homework. The damned thing looks so good it is not even an option to go with a different truck. I am not asking for miracles just 350kms+ on a single tank. $160 per week is too much for gas. Other than gas mileage I have no complaints. It is probably the best looking vehicle i have ever seen let alone owned.

 

Sorry bud but I had a 96 1500 4x4 that was running large tires and I was getting 12 miles to the gallon. CHANGE YOU CAT!!! It might not be bad enough to throw a code or it might not have o2 sensors might be o2 simulators.

 

The model year 2002 Magnum 5.9 V8 is going to have about 8 to 10% worse MPG than a 2002 4.7 V8, and 8-12 % worse than a 2003 5.7 Hemi too.

A 2002 Ram 5.9V8 is also going to have poorer highway MPG than a 2001 Ram 5.9 V8 because the new body style is much worse aerodynamicly
(Cd of model yr 2002 =0.528 and Cd of 2001 = 0.47)

When Car and Driver magazine did a long term test of a truck nearly identical to yours their long term MPG was 12.

http://www.caranddriver.com/article....rticle_id=6695

The only real test for a clogged catalytic converter is to do a backpressure test with the tap for the pressure gauge in front of the cat. Many times you can T into the EGR backpressure sensing line to check this pressure. Pressure at full throttle and 5000 rpm should be less than 6 psiif the exhaust is still stock. Pressure at cruise on the highway at 70 mph should be less than 1.5 psi.

If one or more of your fuel injectors have deposits built up on the tips and are 'dribbling' fuel when they should be off that could cause poor fuel economy.

It is almost impossible to know whether mixed or city MPG is high or low because road conditions and driver habits are so variable.

A better check of the 'health' of your truck by far is
an exactly 60 mph highway 'test run' of a 2002 Ram 4x4 QC 5.9 V8 over 100 miles on a fairly level blacktop highway with wind speeds below 5 mph and air temperatures from 60 F to 75 F. You should get at least 17 MPG in USA gallons from gas pump to gas pump calculating by hand.

If you have the overhead trip computer and its average MPG readout is considerably higher than what you are calculating by hand at the gas pump that is another clue that some of the fuel injectors are dribbling fuel.

If you can find a friend with a diagnostic scanner, or borrow one by leaving a refundable deposit at an autoparts store like Autozone, it is would be well worth checking all 4 O2 sensors, especially if one has already be judged bad. Most O2 sensors don't 'break'. They get poisoned by sufur in gasoline or heavy metals in lube oil or fuel additives.

The front O2 sensors should be 'flipping' rapidly from 0.2 volts to 0.8 volts. This flipping is normal and necessary. The back two O2 sensors should be changing voltage more slowly but still flipping above and below 0.45 volts if they are healthy.

 

Ummyeah what Hank said. He maybe longwinded but gives good tech info!

 

Thanks guys i will give it a go.

 

My friend came over today and brought his scanner with him to check my O2 readings. The front toggled between 0.1 and 1.0 even, while the back did pretty much the same thing! Is that what you meant by toggling bellow and above 0.45 because itis doing exactly that. Or did you mean toggling bellow and above 0.45 by say 0.03 like staying between 0.42 and 0.48?

 

just did the vacum test on the truck to check for a restriced cat/exhaust. I used theHaynes repair manualand vacum gauge. The numbers matched the book to what a perfect running truck should be. I couldnt be more dissappointed thatr nothing needs to be fixed... jk. I guess the next step is to start slapping on aftermarket stuff. Any suggestions???

 

I am not familiar with using a vacuum gauge to check a restricted exhaust.
What steps do you do?

 

I hooked up the gauge by T-ing into the one of the vacum hoses running to the throttle body. Let the engine warm up and jotted down the vacum at idle (18 inHg). Then it said to quickly open the throttle wide open for a moment and quickly release it take note of the reading (needle dropped close to 0 on wide open and then jumped back spiking at 22 inHg before slowly returning to 17 and then staying at around 17.5). It said to repeat the test 3 more times and if the fourth reading is more then 1 inHg lower than the first reading intitially jotted down at idle there might be a restriction somewhere in the exhaust.I did this after taking the truck to the Dodge dealer to get their diagnostic on the catalytic. Guess how they checked it? Yup! They hooked up the computer. Also before checking with the dealer a friend(who is a mechanic)told me and easy way to check for a plugged cat was to check the temperature in front and rear of the cat when the motor is at running temp. He said if the cat is hotter in the front than in the back it could be plugged.I didnt have an IR thermometer so i did the best I could with a multimeter with a temp prong. The cat was 150's in the front 190's in the back. He said that would still indicate it might be plugged since it should be more of a temp difference. I also tried to shake the cat when cold but the damn thing is on so tight with no play soI tapped it with a rubber mallot to hear rattling and i did hearsomesmall vibration inside but I am not sure what it is suppossed to sound like to begin with so it could be normal.

 

If a manual like Haynes or Chilton says that is a valid test
I will give them the benefit of the doubt,
but personally I would be more confident of
a real backpressure test on the highway at full throttle and 4000 rpm.