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Discussion Starter · #1 · (Edited by Moderator)
I really need some help on whats going on with my car and what to do. I am getting 12.8 MPG.

On my Challenger. I do everything in my power to drive conservatively however the highest I could get it was 13.8 MPG even after I reset it.

My car has 100k miles on it. Advice? Can I tune it? New fuel filter.? Or do I straight up just need an engine swap.? I gave it full maintenance and added a cold air intake to help it breathe better, did very little. Plz and thx.
 

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The Bacon Hauler (‘12 Cop Charger)
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The spark plugs are due for a change at 100K. Start with those. That will also give you a chance to access the condition of the inside of the upper intake. If it’s all gunked up, other issues could be at play.
 
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2020 Dodge Challenger Hellraisin Scat Pack
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What Nuke said.

Besides the spark plugs be sure the engine air filter is good. (Let my Hellcat's air filter go to 27.4K miles and then had it changed. It was filthy. And after the engine ran better, had better throttle response. I didn't pay that close attention to the gas mileage.)

Also, if there is a serviceable fuel filter now's the time.

Have to ask: Are you sure about the gas mileage? 13.8mpg is 1-2 mpg less than my 2018 Hellcat delivered.

Do you smell gasoline when around the car? What about when the engine is running?

Just a thought but any chance someone -- family or neighbor -- is helping themselves to some gasoline from your car?
 

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The Bacon Hauler (‘12 Cop Charger)
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The only fuel filter used is attached to the bottom of the fuel pump module inside the left side fuel pump assembly basket. It’s not serviceable per se, so a clogged mesh filter normally requires replacement of whole assembly. But I have experienced a fuel mesh filter being clogged, and it exhibits some pretty significant symptoms, most notably Dead Pedal and at least one DTC related to lean AFR
 

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It also wouldn't hurt to put the car up on jackstands in neutral and make sure all the tires spin freely, a stuck caliper can affect mileage.
 

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Discussion Starter · #6 ·
The spark plugs are due for a change at 100K. Start with those. That will also give you a chance to access the condition of the inside of the upper intake. If it’s all gunked up, other issues could be at play.
I already changed all the spark plugs to BRAND NEW ones as well as cleaned the fuel induction system. Thats why this problem puzzles me. Could there be a part in the car that is worn?

What Nuke said.

Besides the spark plugs be sure the engine air filter is good. (Let my Hellcat's air filter go to 27.4K miles and then had it changed. It was filthy. And after the engine ran better, had better throttle response. I didn't pay that close attention to the gas mileage.)

Also, if there is a serviceable fuel filter now's the time.

Have to ask: Are you sure about the gas mileage? 13.8mpg is 1-2 mpg less than my 2018 Hellcat delivered.

Do you smell gasoline when around the car? What about when the engine is running?

Just a thought but any chance someone -- family or neighbor -- is helping themselves to some gasoline from your car?
Lol no neighbor is siphoning fuel from my car (LOL) and I am the only person who drives it. I do sometimes smell gas tho. But only when I just start the car however from a cold start it goes away in like 15 to 20 sec and thats only when I start the car and stand near the engine not when I'm inside. I just figured its normal.

The only fuel filter used is attached to the bottom of the fuel pump module inside the left side fuel pump assembly basket. It’s not serviceable per se, so a clogged mesh filter normally requires replacement of whole assembly. But I have experienced a fuel mesh filter being clogged, and it exhibits some pretty significant symptoms, most notably Dead Pedal and at least one DTC related to lean AFR
I dont know how to change a mesh filter never done it. how do I check it?

It also wouldn't hurt to put the car up on jackstands in neutral and make sure all the tires spin freely, a stuck caliper can affect mileage.
All 4 tires spin just fine. I do however hear a strange harmonic noise coming from my rear axle I could even hear it from inside the car. I sometimes turn on the radio so I don't have to hear it. (Thats how I found out in the first place)
I exit the vehicle with it on head to the rear beside the rims and I can hear a strange harmonic noise coming from the rear, maybe thats the problem??? I only made an assumption it was the axles.
 

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check for dragging brakes, low tire psi, out of alignment can also cause the tires to scrub, reducing mileage.
driving down hill all the time will greatly improve gas mileage..
ok the last part is a joke. :cool:
 

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Do you do any highway driving? Or is it all stop and go traffic. I'm getting around 19 mpg on my 2017 sxt plus (bought it a month ago). But most of my driving is stop and go. I'm sure it will go way up on the highway.
What rpms are you when going a constant speed. Have you had the transmission checked. Possibly not going into high gear?
 

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Discussion Starter · #9 ·
check for dragging brakes, low tire psi, out of alignment can also cause the tires to scrub, reducing mileage.
driving down hill all the time will greatly improve gas mileage..
ok the last part is a joke. :cool:
I replaced the brakes and checked all the tires, I had my car re aligned 5 months ago, that can't be an issue can it. Can the Mechanic really screw something like that up?

Do you do any highway driving? Or is it all stop and go traffic. I'm getting around 19 mpg on my 2017 sxt plus (bought it a month ago). But most of my driving is stop and go. I'm sure it will go way up on the highway.
What rpms are you when going a constant speed. Have you had the transmission checked. Possibly not going into high gear?
She is my daily driver she shifts just fine (no pun intended) on the freeway. Low rpms (when not in sport mode) driving over 60 mph switches to high gears to lower the rpms like normal stay around 1 to 2 like normal. Could it just be my computer? Or sensor? What are the chances of something like that being faulty. Highly doughtfull.
 

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The Bacon Hauler (‘12 Cop Charger)
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I dont know how to change a mesh filter never done it. how do I check it?
You have to replace one of the fuel pump assemblies inside the gas tank to change that filter. It’s not separately serviceable by itself (the mesh filter).

But you would have other issues, more serious issues, if your fuel pump’s mesh screen were clogged up. Poor gas mileage would not be the main symptom of that. A Check Engine Light and stuttering during acceleration would be present if it were clogged.

What does your daily commute to/from work look like? How many miles each way? How long does it take you to traverse each way?
 

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She is my daily driver she shifts just fine (no pun intended) on the freeway. Low rpms (when not in sport mode) driving over 60 mph switches to high gears to lower the rpms like normal stay around 1 to 2 like normal. Could it just be my computer? Or sensor? What are the chances of something like that being faulty. Highly doughtfull.
It's tough to chase a problem. Back when I was racing for a living.. We wanted to try a set of 5.13 rear end gears. Zoom gave us anything we asked for. We were at an NHRA National Event. And My partner and I would go to manufacturers row to collect what we could get for free. Zoom had a set of 5.13's for a Dana 60 series rear for display. My partner didn't want to wait till they sent us a set. So we convinced them to give us that set.

We put it in the next week and went to Milan Michigan to do so me testing. The car left the line fine but when going up the track it was like a anchor was dragging. We were running 5.38's so "it couldn't have been the gears" right! We looked everything on the car changed transmission and torque converters. Did an alignment The car was so well aligned you could push it on a level surface with your pinky. We changed engines and did everything we could "except change the rear gears".

We fought it for 6 weeks going slow and looking "Dumb". Then at a meet in Columbus Ohio the air quality was terrible the humidity was through the rook and it was 95 degrees. Everyone was looking for higher (numerical) gears. We had a set of 5.57s in the truck that we had carried around for 2 years figuring to use them at an 1/8 mile track. We decided we had nothing lose. I pulled the cover off the Dana. And the ring gear had a beautiful blue color to it. We changed the gears and the car was back to normal. The gears would heat up and bind going down the track. Then cool off on the return road.

We had done many tests for Direct Connection. So we knew how to properly test things, but we didn't follow our own advice. That year we still wound up winning the NHRA World Championship in Stock Eliminator.
 

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Discussion Starter · #12 ·
You have to replace one of the fuel pump assemblies inside the gas tank to change that filter. It’s not separately serviceable by itself (the mesh filter).

But you would have other issues, more serious issues, if your fuel pump’s mesh screen were clogged up. Poor gas mileage would not be the main symptom of that. A Check Engine Light and stuttering during acceleration would be present if it were clogged.

What does your daily commute to/from work look like? How many miles each way? How long does it take you to traverse each way?
Its a 30-35 min drive each day on the freeway. There and back. I go about 70 to 75 MPH. I'm gonna day 20 ish miles. (Maybe more)

It's tough to chase a problem. Back when I was racing for a living.. We wanted to try a set of 5.13 rear end gears. Zoom gave us anything we asked for. We were at an NHRA National Event. And My partner and I would go to manufacturers row to collect what we could get for free. Zoom had a set of 5.13's for a Dana 60 series rear for display. My partner didn't want to wait till they sent us a set. So we convinced them to give us that set. We put it in the next week and went to Milan Michigan to do so me testing. The car left the line fine but when going up the track it was like a anchor was dragging. We were running 5.38's so "it couldn't have been the gears" right! We looked everything on the car changed transmission and torque converters. Did an alignment The car was so well aligned you could push it on a level surface with your pinky. We changed engines and did everything we could "except change the rear gears". We fought it for 6 weeks going slow and looking "Dumb". Then at a meet in Columbus Ohio the air quality was terrible the humidity was through the rook and it was 95 degrees. Everyone was looking for higher (numerical) gears. We had a set of 5.57s in the truck that we had carried around for 2 years figuring to use them at an 1/8 mile track. We decided we had nothing lose. I pulled the cover off the Dana. And the ring gear had a beautiful blue color to it. We changed the gears and the car was back to normal. The gears would heat up and bind going down the track. Then cool off on the return road.
We had done many tests for Direct Connection. So we knew how to properly test things, but we didn't follow our own advice. That year we still wound up winning the NHRA World Championship in Stock Eliminator.
Are you saying I should change my gear ratio,s??? Some 390,s maybe??
 

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The Bacon Hauler (‘12 Cop Charger)
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Its a 30-35 min drive each day on the freeway. There and back. I go about 70 to 75 MPH. I'm gonna day 20 ish miles. (Maybe more)
That should result in higher MPGs than you are seeing...hmmm...

Try this: tomorrow when you leave for work, reset the MPG counter and then watch it as you make the drive. You should see the number fluctuating wildly at first but then settle down after a few miles. What is the avg MPGs you see once that happns?

I would expect you to see somewhere in the high teens or low 20s, but it sounds like you’ll see lower...much lower
 

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Another thing is smell your dipstick, If there is a gas smell, I would do is get your oil analyzed. If you have a couple of cylinders not performing right. It will dilute your oil. The level won't rise dramatically because it will evaporate. But it will stop the oil from doing it's job.
 

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Discussion Starter · #15 ·
That should result in higher MPGs than you are seeing...hmmm...

Try this: tomorrow when you leave for work, reset the MPG counter and then watch it as you make the drive. You should see the number fluctuating wildly at first but then settle down after a few miles. What is the avg MPGs you see once that happns?

I would expect you to see somewhere in the high teens or low 20s, but it sounds like you’ll see lower...much lower
Il try it tomorrow.
 

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I believe it was mentioned before, but make sure you're tires are properly inflated to the proper PSI. That can affect your MPG. With the temperatures fluctuating from winter to spring the tires tend to lose air.

Hope you find the culprit.
 

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Discussion Starter · #17 ·
That should result in higher MPGs than you are seeing...hmmm...

Try this: tomorrow when you leave for work, reset the MPG counter and then watch it as you make the drive. You should see the number fluctuating wildly at first but then settle down after a few miles. What is the avg MPGs you see once that happns?

I would expect you to see somewhere in the high teens or low 20s, but it sounds like you’ll see lower...much lower
Ok I decided to just get in the car and try it.
21.9 was as high as I could get her. Driving very conservatively. Mind you it was raining cats ands dogs outside the air temp was significantly lower. During a normal day in Texas it gets very hot. I could imagine I would make a little difference. The hotter the engine the less fuel efficient it is.

Another thing is smell your dipstick, If there is a gas smell, I would do is get your oil analyzed. If you have a couple of cylinders not performing right. It will dilute your oil. The level won't rise dramatically because it will evaporate. But it will stop the oil from doing it's job.
Il check tomorrow its raining hard outside I can't today

I believe it was mentioned before, but make sure you're tires are properly inflated to the proper PSI. That can affect your MPG. With the temperatures fluctuating from winter to spring the tires tend to lose air.

Hope you find the culprit.
Thx :)
 

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The Bacon Hauler (‘12 Cop Charger)
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Ok I decided to just get in the car and try it.
21.9 was as high as I could get her. Driving very conservatively. Mind you it was raining cats ands dogs outside the air temp was significantly lower. During a normal day in Texas it gets very hot. I could imagine I would make a little difference. The hotter the engine the less fuel efficient it is.


Il check tomorrow its raining hard outside I can't today


Thx :)
Okay, so the car sounds like it’s operating as expected, for the most part. Nothing sounds out of whack in other words.

So the question now becomes what is going the rest of the time that drags that average down so far?

Lots of stop and go would do it. Jackrabbit starts from a stop would do it. Any of that going on?
 

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Using remote start. If it is hot outside, and you do this to get the car cooled down inside, it will affect gas mileage.
 
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