real bad gas milage - Chrysler 300C Forum: 300C & SRT8 Forums
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post #1 of 14 (permalink) Old 12-09-2012, 02:41 PM Thread Starter
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real bad gas milage

ok well here the deal...
im only getting avg 10 mpg on the 300c 5.7 auto
im running 180* thermo
cherry bomb cat back
mopar cold air intake
dioblo 93 octane tune

i know this isnt normal...
i recently changed the plugs and wires. car runs greats!
what can i do here??
also car is on some heavy 22" and its a 2005 300c
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post #2 of 14 (permalink) Old 12-09-2012, 03:12 PM
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What kind of driving do you do?

What I mean is how much highway at cruising in a week? How much stop and go city driving? Does the car idle for long periods?

Also - are you in a colder climate zone this time of year?

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post #3 of 14 (permalink) Old 12-09-2012, 05:22 PM Thread Starter
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What kind of driving do you do?

What I mean is how much highway at cruising in a week? How much stop and go city driving? Does the car idle for long periods?

Also - are you in a colder climate zone this time of year?
its a mix of both really city and highway.. i work less then 10 mins away from work and that city diving rest is all highway really.. most the time i hit green lights all the way to work im in center in st louis mo maybe in the 40* its 48* today

i looked on the preditor for a eco tune for winter but there isnt one..
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post #4 of 14 (permalink) Old 12-09-2012, 06:05 PM
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The 5.7 should get much better mileage, given the conditions. I had two 5.7's and if the engine is revving under 2500 rpm, I would get from 18 - 23 mpg.

I would start with your Predator, by taking the tune out and going back to stock. It doesn't matter if you still have 93 octane in the tank. The ECM will handle that.

I would also make sure the air filter is clean.

I'd run it for a week like that and see what happens . . .
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post #5 of 14 (permalink) Old 12-09-2012, 07:30 PM
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Hey James,
I had the same thing happen with my 05 300C recently. It turned out to be a bad Oil Pressure Sensor. I found out a couple different ways:
1. Used the power on/off technique to get the diagnostic code (would come on sometimes, but not all the time)
2. Hold the two inner buttons on the wheel to get to the advanced screen between the gauges and look at the oil pressure. It will be out of wack. Mine read 99 when it should be around 45-55 psi.
Now... replacing the sensor on your own is bit of a bitch because it is located directly behind the Alternater so you have to take the alternater off and there isn't a whole lot of space to get a wrench in there. If you are doing this yourself, the replacement sensor (if that is the problem) is made of brass and will easily snap off if you over tighten it... sound like I had experience with that... yeah and I was so pissed!!!!
Why do I mention the Oil Pressure Sensor, because if it doesn't work properly MDS never kicks in.
Hope this helps.

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post #6 of 14 (permalink) Old 12-09-2012, 07:33 PM
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That ten minutes from work is what's killing your mileage. The engine never warms up (and letting it idle to warm up isn't going to help). You might try cleaning/replacing the PCV valve. Same for the EGR valve. How are you determining the mileage?
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post #7 of 14 (permalink) Old 12-09-2012, 08:16 PM Thread Starter
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That ten minutes from work is what's killing your mileage. The engine never warms up (and letting it idle to warm up isn't going to help). You might try cleaning/replacing the PCV valve. Same for the EGR valve. How are you determining the mileage?
i remote start the car in the am runs about 5 mins or so and warms up
the mileage is determined by filling up the tank driving 100 miles and then running them numbers... also by the dash as well...

also the oil pressure is fine.. i know about the easter egg on the steering wheel and oil pressure reads just fine..
im just wondering if it isnt the plugs i installed there are ngk copper..
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post #8 of 14 (permalink) Old 12-09-2012, 08:19 PM
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Sounds like a all around tune up is in order... pcv/plugs/wires/check air filter. The oil pressure should be checked as well. Do you feel the mds at all?


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post #9 of 14 (permalink) Old 12-09-2012, 08:32 PM Thread Starter
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Sounds like a all around tune up is in order... pcv/plugs/wires/check air filter. The oil pressure should be checked as well. Do you feel the mds at all?
plugs wires and pcv were changed 5k ago.. and the mopar cold air was install about 7k fliter is clean

ive been all though it all... and cand find the problem...
i think im gonna pull the plugs and see how there firing..
mds idk?
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post #10 of 14 (permalink) Old 12-09-2012, 08:37 PM
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Another thought about the 93 octane tune - my experience with Diablo canned tunes has been very positive - both the 91 and the 93 tune generaly improve engine efficiency and - with an easy foot on the throttle - better mileage.

Perhaps the culprit could be the fuel itself. If it is not to the claimed spec, your mileage could suffer. There has been a few reports here about 'bad' fuel . . .
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