After driving on the highway for about an hour, and then enter into the city where we start to smell exhaust in the cab but cannot see it. This only happens when we come to s stop sign or or a red light. The truck is a 2007 dodge 3500 laramie 6.7 litre. any advice would be very helpful!

Your vehicle has a 15gal. tank. Km per gallon is 45 city and 62 highway. So a full tank should last around 420km around town and 585km highway. If I'm reading your information correctly then sorry to say, no. Is the engine light flashing while you are driving? If so, you need to stop using the SUV and send it in for repair before the engine is damaged. Poor fuel consumption like yours could be related to a leaking fuel injector or fuel line. A valve not seating or poor cylinder compression. Have you noticed anything out of the ordinary? For example rough idle, loss of power, hard start, smoke in the exhaust or the smell of gas? Please let me know if there is anything else.

Could be a fan clutch, sticking thermostat, or restriction in the cooling system including air in the system.

Make sure there are no leaks into the trunk at the rear of the car. When you drive at higher speeds a vacuum is created at the rear of the car and exhaust tends to fill that void. From there it can enter the trunk. Driving with a window open can make it worse.

Have the Exhaust system checked for excessive back preassure and monitor the fuel pressure under the driving conditions you discribed.

I have the same engine. I installed a banks powerpack on it and now I get about 14 on the highway and about 11 city. First thing is a tune up, plugs, wires, fuel filter, air filter, and that sorta stuff. I gutted my intake to let the engine breath better. The banks system opened up the exhaust quite a bit and it has alot more power and get better mileage. A chip can add some fuel economy as well. Any more than simple stuff like that, you'll start getting into serious money. My banks powerpack was $1800 and got me about 2mpg city and about 3 mpg highway improvement. Not much better on fuel but it did get alot more power which means I can be lighter on the gas pedal.

Hi. if your driving time consist of many hours in the city, it will not be required for you to use OD. You can use the regular D in the city, or around town. Using the regular D in town will decrease the unnecessary down shifting that will occur in OD if you are driving in town. The OD function is best used on the Highway, during long periods of travel.

It is also best to use the regular D when pulling up hill, or off road travel, as well.

check 4 spark or fuel pressure

most likely it is the transfer case leaking. known problem on the AWD models. they leak right down on the exhaust and causes the burning smell. have it checked out again.

I would check sparkplugs, plug wires, vacuum hoses to map sensor, check to see if exhaust is strong out pipe, may be a catalytic convertor stopped up , bad O2 sensor will cause starting and idling problems.