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Old 10-10-2017, 04:50 PM   #1
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Location: North Carolina
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Why is my Mach1 getting such horrible gas mileage??

Hi I am new to this forum and I need help figuring out why my mach1 is getting such bad gas mileage. Over the summer I noticed I was filling up my tank more often. Before the problem started I was averaging around 220 miles a tank, now im getting 120 miles. My driving habits are good I do not get on the gas all that often and I do pretty much all city driving. I have done I think almost everything to fix this problem. I have replaced the o2 sensors, cleaned air filter, cleaned MAF, cleaned throttle body and intake, ran fuel system cleaner, and inflated the tires properly. Did all this and nothing has changed, took my car to the ford dealership and they told me the car was having a misfire which was the first thing I check when my gas mileage was dropping but did find anything wrong. Ford fixed the misfire and I could tell right away that the car was running a lot better then before so I thought that was it, problem solved. So I filled up again and now my tank is about empty and the trip is at 125 miles, so nothing changed I am still getting the same bad mileage as before. I am a college student and I just cant afford filling up so often, so if anyone has any idea on what could be causing my gas mileage to be so bad would be greatly appreciated.
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Old 10-10-2017, 07:49 PM   #2
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Join Date: Aug 2002
Location: Baton Rouge, La.
Posts: 15,733
Re: Why is my Mach1 getting such horrible gas mileage??

Have you done a recent oil change, and if so have you checked the oil level and what kind of oil did you use?
In my 125k miles I've put on my car, this has happened once. I used Mobil 1 and it was a disaster.

Krewe de la Mach Rouge

#340804 13th Mach 1 built
11/07/02 Build Date
12/13/02 Delivery
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Old 10-10-2017, 09:44 PM   #3
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Join Date: Nov 2003
Location: Orlando, FL
Posts: 7,970
Re: Why is my Mach1 getting such horrible gas mileage??

does it struggle to start or idle? A blown FRPS (fuel rail pressure sensor) will dump fuel, so much itll contaminate the engine oil but they also usually run pretty rough from my understanding.

how do your spark plugs look? You can have a misfire without it being bad enuogh to trip the CEL but Ford can see it in their tests. Depending on mileage it might be a good idea to just go ahead and put new plugs and coils in it.

I suppose a stuck injector or one thats dumping too much fuel would be a possibility as well but again that usually comes along with a bad idle and other issues.

Does your oil dipstick smell like fuel and as mentioned above is the level higher than fuel (a sign fuel is washing down the cylinders and getting into the oil pan)
03 dsg mach1 - MPR built 9.5:1 motor, D1, cams, ported intake, full exhaust, magnum t56, built rear, E85 etc...

'12 F150 FX2 Supercrew with Ecoboost daily beater
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Old 10-16-2017, 03:59 PM   #4
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Join Date: Mar 2005
Location: Tampa
Posts: 5,653
Re: Why is my Mach1 getting such horrible gas mileage??

Your not running E85 are you?
Just because you're winnin'
Don't mean you're the lucky ones

TR 2003 (Jezebel) sold Mar 12...
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Old 10-16-2017, 05:27 PM   #5
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Join Date: Jun 2004
Location: DFW
Posts: 2,675
Re: Why is my Mach1 getting such horrible gas mileage??

You get more than 100 miles out of tank? Wow, I should be the one pissed. Looks like a keeper to me.

Seriously, the guys above have some good advice, 'smell the oil' and report back.

Fluids and plugs tell most of the story. Good luck
Black '04 Mach 1
Track Times (bone-stock w/drs):60 ft - 1.90 | 1/8 - 8.67
(100 shot,E85,4:10s,Street tire):60 ft - 1.67 | 1/8 - 7.88
New build - 750rwhp; not track tested (yet)
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