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Discussion Starter #1
I've had this Jeep for about 6 weeks. 4 cylinder with a six speed transmission. I love the way it runs but the gas mileage is not what I expected (approx. 20 combined). I'm not too excited about reprogramming it or installing a programmer into the diagnostic 16 pin connector. I see on Amazon that they sell one for a few dollars. I think it's BS myself(I'm an ASE Master Technician). Anyone try one? Any suggestions to help fuel mileage are more than welcome. Thanks
 

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I’ve got the 2016 with the 2.4 liter and 6 speed. I was getting about 23 combined till I put KO2 tires on it. Now I’m down to 20. I was also expecting to get better mileage out of this.
 

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I have a 2014 and in urban driving I get about 20-22, in mixed rural driving I get about 24. However, in highway driving I get 28-30. I am running at the speed limit on the highway and I record all fill ups, and maintenance, using a program called "simply auto." My overall mileage, since I have had the car, is 25.81 mpg. When I look a my last three log entries, they are: 27.19, 25.43, and 27.85. I am a bit compulsive about keeping records.
 

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2018 with 2.4L 9speed auto average of over 36mpg
That's impressive. I've gotten that high on some easy runs with my Compass, but my overall average is 31.4mpg since I've owned it (10,000 miles).

That's even better than my beloved 2008 Patriot 2.4 CVT that averaged about 29mpg though I could eek out 33mpg on a long easy trip.
 

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That's impressive. I've gotten that high on some easy runs with my Compass, but my overall average is 31.4mpg since I've owned it (10,000 miles).

That's even better than my beloved 2008 Patriot 2.4 CVT that averaged about 29mpg though I could eek out 33mpg on a long easy trip.
i have a 55mile each way commute. 95% highway with no redlights
thing seems to love cruise @ 55-60mph

i have noticed a drop in m pg as it gets cooler in the morning, could be air pressure, or just more air in
 

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Its probably engine running richer until heating up. Colder air, higher pressure and more air would increase mpg, not decrease it.
actually colder air would lead to denser air/more air. requiring more fuel to keep from running lean. it would result in an mpg drop

same as if you put a cold air intake on, more air so more fuel required
add on a blower/turbo,more air so more fuel required
 

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i have a 55mile each way commute. 95% highway with no redlights
thing seems to love cruise @ 55-60mph

i have noticed a drop in m pg as it gets cooler in the morning, could be air pressure, or just more air in
Yeah, I've noticed mine gets much better fuel economy under 60mph. Also, the a/c really sucks gas -- I'm guessing it chops off 2-3mpg.
 

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actually colder air would lead to denser air/more air. requiring more fuel to keep from running lean. it would result in an mpg drop

same as if you put a cold air intake on, more air so more fuel required
add on a blower/turbo,more air so more fuel required
Unless you do a complete reprogram, the ECM compensates for everything. That's why all these mods are only placebo effect -- there's no real difference in performance.
 

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actually colder air would lead to denser air/more air. requiring more fuel to keep from running lean. it would result in an mpg drop

same as if you put a cold air intake on, more air so more fuel required
add on a blower/turbo,more air so more fuel required
Denser air also provides higher compression and therefore more power per fuel injection, or. stroke What you said is true if you run both engines at same speed. But a turbo engine for instance, can generate enough power at 2000 RPM that a non-turbo one generates at 3500 RMP. So overall, you can theoretically still have higher mpg. However, in the the real world, engine design constrains and cost generally make turbo gasoline engines of regular cars less efficient than the equally sized naturally aspirated variant. This is not due to an inheritor inability, but because of cost and design. Most turbo engines on cars are designed to run rich on fuel when turbo kicks in. So they actually have incomplete burning and are less efficient. They program these engines run rich because a complete burn would generate more heat and pressure and put more stress on the engine, and they would also be very prone to pre-ignite and knock if a lean air-fuel ratio is used. An engine can be designed to run lean with turbo, but the additional weight of beefed up engine and cooling system, plus the cost, makes it illogical produce such an engine. It is a lot cheaper to make a slightly small turbo engine or slightly large turbo engine depending on if you want more economy or power. Overall, turbo diesel engines (where engine knock is not an issue) and turbo gas engines of prop airplanes (which are operated at very low temperatures) are more fuel efficient that equally sized naturally aspirated variants. So it is possible to design such an engine, but it is not cost effective for a regular car.

It wont work the same way for cold ambient air, except when engine when its cold. Once the engine heats up, it will also heat up the air going into the combustion chamber, so the compression will more or less be the same regardless of ambient temperature. Cold air intakes try to get over this but the improvement in power is rarely more than 1% since the majority of the heating and expansion happens once the air hits the hot engine block around the valves. And since engine block temperature is more or less the same for a heated engine regardless of weather, ambient temperature of the air is negligible. ECM does inject more fuel when the engine is cold to run a rich mixture. Because that is the only time when air going into the combustion chamber is colder and denser(and cutting back the air going into the chamber would cause knocking).



correct, and that compensation for colder is more fuel.
Not necessarily. Any engine with a MAF sensor can also reduce the air going into the cylinder. And its easier to reduce the air going in than increasing the fuel. Because increasing the fuel would cause the engine to generate more power per stroke and it is a lot more difficult to control engine that is generating variable amounts of power per stroke than one that is generating equal power. Otherwise the the car would speed up and slowdown on its own without you giving or cutting the throttle. Like I said before,more fuel is injected to a cold engine to run it rich, and this is to prevent knocking.

I think the main difference in drop in mpgs in cold weather is due to longer period engine runs rich and the fact that colder air is denser and cause more drag. Especially at higher speed like in your case. Also check if you state switched to winter blend gasoline which has a bit less energy.
 

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Denser air also provides higher compression and therefore more power per fuel injection, or. stroke What you said is true if you run both engines at same speed. But a turbo engine for instance, can generate enough power at 2000 RPM that a non-turbo one generates at 3500 RMP. So overall, you can theoretically still have higher mpg. However, in the the real world, engine design constrains and cost generally make turbo gasoline engines of regular cars less efficient than the equally sized naturally aspirated variant. This is not due to an inheritor inability, but because of cost and design. Most turbo engines on cars are designed to run rich on fuel when turbo kicks in. So they actually have incomplete burning and are less efficient. They program these engines run rich because a complete burn would generate more heat and pressure and put more stress on the engine, and they would also be very prone to pre-ignite and knock if a lean air-fuel ratio is used. An engine can be designed to run lean with turbo, but the additional weight of beefed up engine and cooling system, plus the cost, makes it illogical produce such an engine. It is a lot cheaper to make a slightly small turbo engine or slightly large turbo engine depending on if you want more economy or power. Overall, turbo diesel engines (where engine knock is not an issue) and turbo gas engines of prop airplanes (which are operated at very low temperatures) are more fuel efficient that equally sized naturally aspirated variants. So it is possible to design such an engine, but it is not cost effective for a regular car.

It wont work the same way for cold ambient air, except when engine when its cold. Once the engine heats up, it will also heat up the air going into the combustion chamber, so the compression will more or less be the same regardless of ambient temperature. Cold air intakes try to get over this but the improvement in power is rarely more than 1% since the majority of the heating and expansion happens once the air hits the hot engine block around the valves. And since engine block temperature is more or less the same for a heated engine regardless of weather, ambient temperature of the air is negligible. ECM does inject more fuel when the engine is cold to run a rich mixture. Because that is the only time when air going into the combustion chamber is colder and denser(and cutting back the air going into the chamber would cause knocking).





Not necessarily. Any engine with a MAF sensor can also reduce the air going into the cylinder. And its easier to reduce the air going in than increasing the fuel. Because increasing the fuel would cause the engine to generate more power per stroke and it is a lot more difficult to control engine that is generating variable amounts of power per stroke than one that is generating equal power. Otherwise the the car would speed up and slowdown on its own without you giving or cutting the throttle. Like I said before,more fuel is injected to a cold engine to run it rich, and this is to prevent knocking.

I think the main difference in drop in mpgs in cold weather is due to longer period engine runs rich and the fact that colder air is denser and cause more drag. Especially at higher speed like in your case. Also check if you state switched to winter blend gasoline which has a bit less energy.
That's a whole lot of copying and pasting there. You should at least quote your sources when you do that.
 

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I've had this Jeep for about 6 weeks. 4 cylinder with a six speed transmission. I love the way it runs but the gas mileage is not what I expected (approx. 20 combined). I'm not too excited about reprogramming it or installing a programmer into the diagnostic 16 pin connector. I see on Amazon that they sell one for a few dollars. I think it's BS myself(I'm an ASE Master Technician). Anyone try one? Any suggestions to help fuel mileage are more than welcome. Thanks
Back to the OP's question, here's a suggestion. Try the poor man's reset: disconnect the battery for an hour or so. That should clear the computer and let it reset. Then drive like an old lady for the next 200 miles (sorry Grandma). The computer should learn your driving style and adapt. The previous owner may have driven like a flying rodent escaping the underworld and the ECM learned that style. A lot of people complain that the Compass isn't a sports car, and its not, but if someone tries to make it perform that way it will do its best.

Hope that works. "Free advice costs nothing and its worth the price"
 

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Discussion Starter #18
Thanks for your input Jasmine. I am familiar with the adaptive learning on the Compass and other vehicles as well. I will report back with my findings after the test. BTW everyone, the computer allows a rich mixture to happen when the engine is cold to ALLOW IT TO START! Ever heard of a choke plate on a carb? It does the same thing. Also depending on ambient temperate, the injectors will be open longer due to a longer injector on time driven by the ECM.
 

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Thanks for your input Jasmine. I am familiar with the adaptive learning on the Compass and other vehicles as well. I will report back with my findings after the test. BTW everyone, the computer allows a rich mixture to happen when the engine is cold to ALLOW IT TO START! Ever heard of a choke plate on a carb? It does the same thing. Also depending on ambient temperate, the injectors will be open longer due to a longer injector on time driven by the ECM.
I used to put hand chokes on my carbureted cars to aid starting in the winter and save gas once I was moving.

I also notice it takes a long time to get these things fully warmed.
 

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The previous owner may have driven like a flying rodent escaping the underworld and the ECM learned that style.
the funniest thing I've read here for a while
 
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