Nitecap

Just bought my first CTD. '99 Ram 2500 longbed 4X4, 24V CTD, 5-sp manual. It has 116K miles on it. The previous owner was hauling something heavy - its got lower rear-end gears, rigged for 5th wheel, electric brake controller, and Power Max (TCI Products) chip. I think its also had leaf springs added. Its got mudder tires on it as well.

So, I was under the impression that I would get better mileage than my '98 Expedition, which got about 12 MPG. I just filled up the second time. Went 271.4 miles, and put 20.91 gallons of diesel in it. That comes out to just under 13 MPG.

So why the crappy gas mileage? Big tires, low rear-end, and used the 4WD for two days last week in the snow... How about the Power Max chip? Will that cause a degrade of mileage?

We'll be towing a 30' cabin cruiser (about 13K lbs) a couple of times/year. Thats why I bought the truck. I just thoght that when I wasn't towing, the gas mileage would be somewhere between 16 and 18.

Any help??

Mopar1973man

There is a lot of thing that effect fuel mileage...

• Air up your tires
• Don't jump on the skinny pedal to hard
• Winter fuel
• Don't drive fast keep it under 2K on the tach
• Oversized tires will degrade MPG numbers
• Overall weight of the truck
• Fuel & Air filters (have they been changed)
• MAP & IAT sensor failed, dirty or sooted. (Check for codes)

These are just a few thing that effect the MPG of the truck.

Geico266

Get a fuel pressure guage ordered today. You can't drive a "99" without it and know when the lift pumps dies. The truck will keep running only to take out your $1,600 injector pump.

Use the search mode here for tons of info on your truck. The mileage seems normal for your gears & time of the year. Winter blended diesel is not as good for mileage. You will be able to tow that boat with no problem at all. Make sure your trailer brakes work properly though. The "99" rear brakes are weak to say the least. You might want to search 1 ton GMC wheel cylinder for a cheap rear brake upgrade.

Welcome to DTR!
May you have 1,000 posts before you read about Hoss and his concrete bed liner, 5erBob and his Speedos, or Beagle and his CTD Gremlin! We have all kinds on this site.

I'm the normal one around here.

John Faughn

That sounds like the millage is off , by low gears what are they ? ratio , about that time it seems that they had 3.73 or 4.10 , I like my 3.54 , with the mods we can do the lower #s are good for millage and then turn around and make more HPs and your good to go. so with out more info its hard to say . Also welcome.

Nitecap

I'm pretty sure the gears are 3.54. I don't really know how to check. Kinda new to this stuff!! Previous owner did a bunch to beef it up for towing. The added leaf springs are obvious - how do I check the gear ratio?

What is the MAP & IAT sensor?

Fuel guage. I'll make sure I get one!! No need to have the pump go out.

A couple of things could have affected my mileage on this tank. It was VERY cold here last week in Denver. It snowed, and we had sub-zero temps for half a week. This means I was in 4WD, plus letting the truck idle to warm up quite a lot.

The motor does idle a bit rough. Its not nearly as smooth as my best friend's 12-valve CTD ('96 2500). I am wondering if its that Power Max chip. I've heard if they go bad, it will degrade engine performance and mileage in a big way. My friend is getting 17-19 in the city. I kinda thought I would be at least close to that...

Thanks!!

John Faughn

To find the gear ratio , look at the cover for the r. differential , there should be a metal tag held on by one of the bolts that hold the cover on , right down all thats there and put in note book that you keep for all the truck info [part #s ect] , with colder weather most of the refineries have a winter blend and that you get a little less mpgs , also the other stuff you mentioned , for the ruff idle you should have the valve adjustment checked along with every other maintance stuff so you know what to do in future [ get on a scedual] , with the valves not adjusted right you'll have a little less HP and a ruff idle. the MAP is manifold asblolute pressure, the IAT is intake air temp. for this and alot more go to the top of the page and and link to the tech facts , you should also co to user control pannel and fill in the info on truck so that we can help you easyer.

RickCJ

Are the tires bigger than stock? is the speedo correct?

CoastalDav

The map sensor provides info to the computer about the Turbo boost in the system. The IAT sensor tells the computer what the air temp is in the boost system. (air intake)

A bad map sensor will make the truck run like Dog Doo. A bad IAT sensor will cause poor fuel mileage, how bad ??.

Here is some info on the IAT Sensor

http://www.smokindiesel.com/Technical.htm

Hear is another http://www.dodgeram.org/tech/dsl/sensors/IAT/clean.htm

There are many other such articles for your truck at the above address.

Dave

eric13

Another way to get your gear ratio is to look in the glove compartment snd there should be a tag stuck to the inside of the lid and it will have your gear ratio on it.

Spiderfarm

Mudder tires AND 5th wheel towing? Those features dont mix well. You will probably want to get decent load rated Highway tires for your towing 13K Lbs. Mudders float and wont have strength or stopping power to keep you straight when towing. Also lots of rolling resistance.

You also mentioned cold idling. Major fuel consumer - cold idle. Cut your warm=up time with the block heater and / or Grill cover.

Sounds like you have a longer wheelbase than your Expedition which should tow you cruiser with less "wag" too.

You dont have a 5th wheel boat trailer, do you?

FRANKV569

I am not the "all knowing" here but, when I read about your rough idle, it reminded me of our 2000 ram ctd. After a new lift pump and vp-44 were installed. a short while later it developed a "rough idle" ans stumble. Through further analysis, i found that i had a failed injector and proceeded to replace all six (easy job). rough idle went away and never came back. as far as the gear ratio, two other methods come to mind. first, stop into your local dealer service department with your v.i.n. and they can print you the entire "build or options" list sheet in a matter of seconds for free. that way, you will know if it has the dhd transfer case, snow plow prep group, gear ratios, camper package (extra rear leafs i believe are in that package), s/n of engine, build date of engine, recalls and tsb's that were completed or need to be, etc. when my dealer printed mine, it had the original owners name and address (i didnt tell them i just bought it so they left it on) so i was able to give the guy a call and talk about the truck and learn the "true" history. the second way is... if you are like me and immediately change every drop of fluid and filter of a "new to you" vehicle when you buy it, when you pop off the rear diff cover you may see: "a number/ another number stamped i believe on the ring gear somewhere? do the math with your calculator and it will be your ring and pinion ratio. being that its a "matched" gearset, the one number before the forward slash (/) is how many teeth are on the ring gear. the second number-after the slash is how many teeth are on the ring gear. do the simple division, and you get your ring and pinion ratio.... i.e. 3.54:1, 3.73:1, 4.10:1, etc. hope that this helps!