The TCM controls the transmission which also affects the shifting and shift points in the trans., so in a nut shell, yes it could cause poor fuel mileage. TPS, O2 sensors, spark plugs, pcv valve, and air filters also affect fuel mileage. Oh and the biggest thing that really affects it is a lead foot. How was your Durango shifting before? Are you sure that the TCM is bad or PCM?

 

Replace the spark plugs with Regular Champion Copper spark plugs (yes the $2 specials!) and gap them at .040 for the best results. There are 8 spark plugs and no wires on the 4.7L so just replace the plugs. Don't get anything else especially when diagnosing an issue. Also you can replace the PVC valve.

 

I'm sure the TCM went bad. I took it to a repair shop and they found it. They wanted to charge $600 for everything but I found one online for $200 and they'll program it. It used to shift hard and lately I've noticed that sometimes when its in drive it will shift itself to 2nd. As far as the spark plugs go I bought platinum plugs so I need to change those out. Thanks 45AutoPete and hydroshocker for the advice.

 

Do what you will but I told ya so.


That motor was never designed to run Platinum plugs. However, some say that Champion Iridium plugs or Champion Platinum plugs will work only in the 4.7L but I have seen too many issues including gas mileage issues, CEL's, and even blowing up motors so do what you will.

The ONLY plugs I like are Champion Coppers (OEM) or Champion Truck period.

 

Yeah I thought the platinum were the best, but it looks like I'll be buying some copper ones this weekend. Does anyone have any suggestions on additives for my D?

 

If she's running fine, don't mess with it. Only additive I did was switch to M1 full synth. ...
Oh yeah, homebrew CAI and K&N filter...

 

nope dont put any aditives in the oil, every now and then a good fuel injector cleaner (techron ect) cant hurt, but dont make it an every tank thing, once a year should be plenty

 

I would change em out and take them back and get your money back. Tell them they would not work worth a crap. NAPA sells the Champion Truck plugs.


As for additives.........Don't do it!!!!!!!!!!!!!!!!!!!


Additives are like herbs. They are not regulated by the Government. They can put anything into that crap and sell it for money. It states right in your owners manual NOT to use them. Now here are some good suggestions:

Oil is regulated so you know your getting what you pay for. Switch over to Mobil One Fully Synthetic 10W-30 as my favorite choice. In reallity you can go with a good name brand and get a good oil but I know for a FACT they use (PAO's) which is a true Synthetic (the best kind) for a great price. You can get it at Walmart for $22.50 for a 5 quart container right now. Get a good filter like Bosch, Mobil One (full synthetic is the best but at $12 bucks isn't worth it) or a K&N or similar. Stay away from FRAM.

Next, you can buy a bottle of Seafoam and pour it in the gas tank or even Techron are great products if you are going to use them (I don't like any of them but if I use them (in a blue moon) that is what they are). I like Chevron fuel.

Have the transmission fluid and filters replaced and never flush it!!!!! Make sure they only use ATF+4 and not multi-vehicle fluid.

Change out your rear differential fluid with 80W-90 hypoid gear oil or even better 75W-90 Mobil One LS hypoid gear oil. Now if you have a Limited Slip differential go to Auto Zone and buy their 7oz bottle of Friction Modifier for $4.99 and use the whole bottle.


Now have a great time here on the boards!......