Sudden drop in Gas mileage
 

I need help please .... Ok First about the truck:

1995 4x4 1500 Ram truck 5.9 engine all stock
132,000 original miles
1500 miles ago complete tune up. (did not do any sensors)
On a recent leg of a trip got over 16mpg in town 12.5-13mpg all the time.

Last two tanks 10.1 mpg I did not change the way I drive in any way at all .. to old lol at 68 yrs old.

Checked codes just now: threw a 12, 21, and a 32 Check engine light comes on sometime but goes off when I stop and start again.

Only other thing I can add driving around where I live often is at 50-55mph. At 50 it will go into overdrive. Lately I feel a stumbling .. I'd almost call it the 4x4 ride bumpty bumpty bump down the highway ride. Though this is not all the time. So that's why I know or feel it's not in the drivetrain and guess it's an engine stumble.

O2 sensor? and by the way all I can find is one .. just before the cat on the passenger side.

The gas-mileage change is in the last two tanks ... it's sucking down the gas big time.

HELP!

Dan

replace your plenum with a hughes engines plenum kit. Replace the 02 sensors as well. if your getting consistent 10 across the board no matter the way you drive, then your plenum is blown to crap. Take a look down your throttle body and if you see any oil pooling or a good amount of oil, the plenum is toast. If you don't see any, then i would start looking at your catalytic converter and o2s. However i would put in the hughes kit anyway, cause that plenum is gonna go anytime.

"Checked codes just now: threw a 12, 21, and a 32" this doesnt help too much by the way. need exact numbers on the codes to give you best possible help.

His is OBDI, those ARE the codes. :)

12 is normal, 21 is an O2 code. (stays at center, or shorted to voltage. basically, it's dead) 32 is EGR solenoid circuit short, or open. I.E. EGR isn't working. That shouldn't have to much of an affect on gas mileage, but, the O2 sensor certainly will.

ah crap forgot ob2 was pre 96

Thanks Guys,

I will look down the plenum. I hope it's ok. It is my understanding the plenum was fixed at 110,000 miles by the previous owner .. I've got the receipt from the work.

So back to a portion of my question no one naswered .. I only found one sensor. I've read in one place (I think) that there is only one o2 sensor just before the cat. In other places I hear, no there is two.

How many O2 sensors do I have and how does anyone know which one to replace? Obviously if I only have one then I have my answer.

Dan

If the "fix" was just put a new gasket in, then it is blown again.

there are two, an upstream and downstream. from my experience the one before the cat is usually the troublemaker, however if your plenum blew and they never got replaced, then they probably are both dead, and itll kill your cat next.

Yup, that's why the recommendation is to change sensors and cat at the same time, even if you don't think it is needed.
Bad sensors will kill a cat pretty quick.

C'mon guys. His is OBDI. He only has one O2 sensor, pre-cat. :D If you make him keep looking for the second one, he is going to grow old, and die, laying under his truck, trying to find something that isn't there. :D

lol dammit. i keep assuming the 94-97 models are the same