Kinda seems like my fuel economy dropped in the past few weeks... anyway to fix that without buying upgrades??

My truck is a stock 2001 3.9L Sport.

 

normal maintenance, plugs, wires, etc,

 

I know there is an argument it doesn't work but I switched from 87 to 89 and saw about a mile increase and less pinging. This is with my superchips on 87 mode so I'm thinking with my high mileage it was pulling to much timing or something. I have an app that shows my fill ups each time and I went from a solid 19.2 mpg to 20.12 mpg the last two fill ups (I drive about 35 miles round trip easy no hard accelerations, everyday)

 

87 to 89??

 

Here comes the big discussion but throw some sea foam in, some people agree others dont, change oil, last quart use oil treatment

 

It could also be a lazy O2 sensor, they do read differently with age and that can cause lower MPG. It can also be a lazy or worn out MAP sensor. The center wire on the MAP should read over 1.5 volts at idle. Anything less and the sensor should be replaced. A lazy O2 and/or a weak MAP sensor signal can both be detrimental to MPG and neither one will always set a trouble code or a CEL. Maybe check out this thread:

https://dodgeforum.com/forum/2nd-gen...er-solved.html

As the others mentioned, a good tune-up could help too. Maybe check and replace your air filter if it needs it. Keep the right pressure in your tires. I tried running 42 psi in mine to increase MPG, it helped a little but it also wore out the center treads prematurely. Make sure the alignment is in specs. Use good quality gas from a station that changes its pump filters on schedule and sells a lot of gas so the gas you buy is always fresh.

Since someone else mentioned a fuel system additive I will just say that in my own experience with my truck I get better MPG with a dose of Marvel Mystery Oil in my gas. I add 4 ounces of it to every 10 gallons of gas at every fill-up. Some people do not like MMO, some are indifferent. As they say, "some swear by it, some swear at it." I have been using it almost two years now, I track my MPG on www.fuelly.com and I can say without a doubt I get an extra 1 to 2 MPG with MMO in the tank, I usually average between 17 and 19 combined city and highway driving. MMO can help improve compression and power by helping to provide a better piston ring seal. I get a nice smooth even idle with it. You can also add it to your oil but I won't go into that here. MMO will help restore the lubricity that is lost in fuel from the use of ethanol. If you try MMO you might need to use it for a few tanks before you see any benefit from it. It is also best to either have a fuel system service done first or at least use a good strong in-tank fuel system cleaner before starting on MMO. The idea is to get the system clean with a good cleaner treatment first then keep it clean with regular use of MMO. Some people use it and get good results, some do not. Same with any other additive.

Maybe try a good fuel system cleaner in the tank. Personally I like Gumout Regane, you can buy it at any parts store. It has a high concentration of PEA, which is some unpronounceable amine compound that does the best job of cleaning fuel injectors. High Mileage Regane has an even higher concentration of PEA. I have never used the HM version. Red Line SI-1 is good too, it has a lot of PEA in it. Those are about the best of the in-tank fuel system cleaners. The others like STP and Prestone are all mostly just kerosene and don't really offer much benefit. I run a bottle of Regane about twice a year. It does a good job.

It might also help you to have a fuel system induction service done. You can get the BG Induction Service or Everwear Service done at most tire stores or garages. If you want to try a BG service you can visit www.bgfindashop.com. There is also a DIY 3M fuel induction kit you can buy at Autozone for about $30.00. I have no idea how well it works but 3M is a good brand name.

These are a few things you can do to try to improve MPG. Others here may have more info on it for you.

Jimmy

 

Any changes to the truck made before the notice of fuel milage decrease?

 

My check engine light just came on last night so i'm guessing it's the O2 sensor!! I notice on monday that my fuel mileage sucked then last night (Wednsday) my check engine light came on!!!

Thanks a lot guys... I'll update as things go, the shop cant get my truck in till next tuesday to plug it in. it seems to run smoothly so as long as that's happening it can wait till then.

I'm hopeing to get a air intake, spacer, and a tune up kit (plug wires, cap, and plugs) by the end of summer!

 

You don't need a shop to read your trouble codes. Turn the ignition key from "off" to "on/run" and back off 3 times in a row, on the third time leave the key in "on/run" and your trouble codes will display in the odometer. If there is more than one code it will display them all in succession then when finished it will say "P Done" in the odometer. Write down the codes and check the code lists in the FAQ section at the top of the Second Gen page here and you will get an idea of where to start with fixing the truck. Post here again if you have any questions or need some help.

Not trying to tell you your business but I would not waste money on a TB spacer. They don't do anything for the 3.9.

Jimmy

 

Thanks Jimmy... will try that out.

Will it also clear the check engine light??