Poor 14 MPG Gas Mileage on my 2004

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O

OSKY

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Last seen
Joined
Mar 27, 2019
Thunderbird Year
2004
I'm getting "ONLY 14 MPG."

I bought the car almost 13 mo. ago with 49,933 as of today, it has 51,682, (1,749 driven thus far).
The previous owner had installed a "69-3520TP K & N Performance Air Intake System", (the filter is clean)
When I got it, it was giving me 17 MPG, 95% of my driving then and now is in the City, normal driving of 30-55 MPH depending on the road, no lead foot, including at traffic lights or stop signs when accelerating, also I hardly ever use the A/C and I keep the " Hard Top" on all the time with both windows rolled down.
The car drives like it was a new car just like when I bought it, there has never been any kind of check engine warning lights come on or any strange noises coming from the engine.
The only thing that I had to replace was the battery back on 9/1/19.
I keep my tires PSI at 32.
I have driven a full tank of gas on "D4" and another full tank on "D5" and there was no improvement, still 14 MPG.
I also added a can of "SEAFOAM' on each full tank, again no improvement.
I'm at a loss of why the poor MPG.
Any suggestions, tips on what to check or do will be appreciated.
Thank you in advance.
 
OSKY said:
I'm getting "ONLY 14 MPG."

I bought the car almost 13 mo. ago with 49,933 as of today, it has 51,682, (1,749 driven thus far).
The previous owner had installed a "69-3520TP K & N Performance Air Intake System", (the filter is clean)
When I got it, it was giving me 17 MPG, 95% of my driving then and now is in the City, normal driving of 30-55 MPH depending on the road, no lead foot, including at traffic lights or stop signs when accelerating, also I hardly ever use the A/C and I keep the " Hard Top" on all the time with both windows rolled down.
The car drives like it was a new car just like when I bought it, there has never been any kind of check engine warning lights come on or any strange noises coming from the engine.
The only thing that I had to replace was the battery back on 9/1/19.
I keep my tires PSI at 32.
I have driven a full tank of gas on "D4" and another full tank on "D5" and there was no improvement, still 14 MPG.
I also added a can of "SEAFOAM' on each full tank, again no improvement.
I'm at a loss of why the poor MPG.
Any suggestions, tips on what to check or do will be appreciated.
Thank you in advance.
Click to expand...
I don't want to offend but realize that this car requires premium gas
 
OSKY said:
I'm getting "ONLY 14 MPG."

I bought the car almost 13 mo. ago with 49,933 as of today, it has 51,682, (1,749 driven thus far).
The previous owner had installed a "69-3520TP K & N Performance Air Intake System", (the filter is clean)
When I got it, it was giving me 17 MPG, 95% of my driving then and now is in the City, normal driving of 30-55 MPH depending on the road, no lead foot, including at traffic lights or stop signs when accelerating, also I hardly ever use the A/C and I keep the " Hard Top" on all the time with both windows rolled down.
The car drives like it was a new car just like when I bought it, there has never been any kind of check engine warning lights come on or any strange noises coming from the engine.
The only thing that I had to replace was the battery back on 9/1/19.
I keep my tires PSI at 32.
I have driven a full tank of gas on "D4" and another full tank on "D5" and there was no improvement, still 14 MPG.
I also added a can of "SEAFOAM' on each full tank, again no improvement.
I'm at a loss of why the poor MPG.
Any suggestions, tips on what to check or do will be appreciated.
Thank you in advance.
Click to expand...
I have been through this also when my 2005 went down to 17 mpg. I worked systematically one or two things at a time. Replaced fuel filter in driver's side wheel well, changed plugs and cops, (oil was in one of the spark plugs wells,) replaced VVT solenoids, cleaned MAF and throttle body, oil and filter 5/20 oil, cleaned and lightly oiled K&N filter, disconnected battery and did the relearning procedure, polished the car yada yada. Eventually mileage went back to the normal 21-22mpg around town and 27-28 on a trip. I have no idea what made the difference, it just came back to a decent figure over time?
Ian
 
I agree with tbird Clean the mas air flow sensor. The K & N Filters tend to contaminate the sensor. If the plugs and COPs have never been replaced ... now is the time.
The throttle body may need cleaning and re-calibrating.
Its probably a good Idea to monitor your fuel trim that will tell you if there is a vacuum leak or if the oxygen sensors are working correctly.
Stay away from those additives your asking for trouble. Just use a Tier-1 top quality Premium fuel. (Sunoco Ultra)
 
An over oiled K&N causes issues on a lot of Mass flow sensors. Check all the clamps on your induction/intake system too. Just picked up an 02 for the wife and replaced the AF. When I was flexing the intake to remove the MAF for cleaning with CRC MAF cleaner I noticed the intake was also loose at the throttle body. Tighten it up two turns! Hard part is slowing my wife’s roll while I try to check this bird over!
 
OSKY said:
I'm getting "ONLY 14 MPG."

I bought the car almost 13 mo. ago with 49,933 as of today, it has 51,682, (1,749 driven thus far).
The previous owner had installed a "69-3520TP K & N Performance Air Intake System", (the filter is clean)
When I got it, it was giving me 17 MPG, 95% of my driving then and now is in the City, normal driving of 30-55 MPH depending on the road, no lead foot, including at traffic lights or stop signs when accelerating, also I hardly ever use the A/C and I keep the " Hard Top" on all the time with both windows rolled down.
The car drives like it was a new car just like when I bought it, there has never been any kind of check engine warning lights come on or any strange noises coming from the engine.
The only thing that I had to replace was the battery back on 9/1/19.
I keep my tires PSI at 32.
I have driven a full tank of gas on "D4" and another full tank on "D5" and there was no improvement, still 14 MPG.
I also added a can of "SEAFOAM' on each full tank, again no improvement.
I'm at a loss of why the poor MPG.
Any suggestions, tips on what to check or do will be appreciated.
Thank you in advance.
Click to expand...
I have my 03 for 5 years, nothing but High Test gas, 3.9 Jaguar Engine, an I get 25 MPG, at 70MPG, Top up or down no difference, check your gas filter, clean your K&N filter, might need new Plugs, You could try a can of Seafoam, with a full tank and see if the injectors get cleaned out
 
Anthony C said:
Just use a Tier-1 top quality Premium fuel. (Sunoco Ultra)
Click to expand...
Another car I have is a "Flex Fuel" and is able to run on the lower octane Ethanol. I tried it and mileage went down. Lower octane fuel = lower BTU output. No real $ savings. Cost per gallon is less, but uses more fuel to do the same work, meaning less MPG. Also, double check the dash readout by doing it the old way with a math problem of dividing miles driven by gallons used. If one of the computer inputs if off the dash number will also be off. For me, I don't drive it enough to be worried about the mileage from a cost savings standpoint, but I would be concerned that a mechanical issue may need addressed.
 
tbird said:
Clean your Mass Air Flow Sensor, make sure you use MAF cleaner to avoid damaging the sensor.

Also, how are your COPS & spark plugs? Those are troublesome on these cars.

What size are your tires?
Click to expand...

TBIRD, I will follow your suggestions by cleaning the "MAFS' first, once I find out where it's located.

And according to the CARFAX Vehicle History Report that I have, COPS and the Wiper Motor Bracket Seal were replaced on 8/19/15 under the #07N09 Extended Warranty Coverage program that Ford had, I'll call Ford on Mon. to see if they can give me any info on how many were replaced and the number of them, no spark plugs were replaced that I can see but I'll also ask about them.

The tires size that came with the car when I bought it is 235/50R/17 96V Bridgestone -Turanza- Serenity.

Thank you for your advice, TBIRD!!!

JohnS said:
I don't want to offend but realize that this car requires premium gas
Click to expand...
Premium gas, 93 Octane is what I pump into it, I meant to include that in my post because I knew someone will ask about it but I failed to add it, no offense taken whatsoever, John.
Thanks!!!
 
Last edited by a moderator:
OSKY said:
TBIRD, I will follow your suggestions by cleaning the "MAFS' first, once I find out where it's located.

And according to the CARFAX Vehicle History Report that I have, COPS and the Wiper Motor Bracket Seal were replaced on 8/19/15 under the #07N09 Extended Warranty Coverage program that Ford had, I'll call Ford on Mon. to see if they can give me any info on how many were replaced and the number of them, no spark plugs were replaced that I can see but I'll also ask about them.

The tires size that came with the car when I bought it is 235/50R/17 96V Bridgestone -Turanza- Serenity.

Thank you for your advice, TBIRD!!!
Click to expand...

When you reply to a topic, don't remove the Quote code, it messes up the quote. I fixed your reply.

Changing the COPS 1/2 a decade ago doesn't mean they are okay now. As everyone will confirm, they are problematic, especially if there is a leak in the cowl seal too. People will often replace the COPS and have another underlying issue.
 
OSKY said:
I'm getting "ONLY 14 MPG."

I bought the car almost 13 mo. ago with 49,933 as of today, it has 51,682, (1,749 driven thus far).
The previous owner had installed a "69-3520TP K & N Performance Air Intake System", (the filter is clean)
When I got it, it was giving me 17 MPG, 95% of my driving then and now is in the City, normal driving of 30-55 MPH depending on the road, no lead foot, including at traffic lights or stop signs when accelerating, also I hardly ever use the A/C and I keep the " Hard Top" on all the time with both windows rolled down.
The car drives like it was a new car just like when I bought it, there has never been any kind of check engine warning lights come on or any strange noises coming from the engine.
The only thing that I had to replace was the battery back on 9/1/19.
I keep my tires PSI at 32.
I have driven a full tank of gas on "D4" and another full tank on "D5" and there was no improvement, still 14 MPG.
I also added a can of "SEAFOAM' on each full tank, again no improvement.
I'm at a loss of why the poor MPG.
Any suggestions, tips on what to check or do will be appreciated.
Thank you in advance.
Click to expand...
I don't know but my 2005 with 25000 miles always gets 14 mph
 
My 2005 gets 15 around town and 18 to 21 on the highway. That's top down as I never have it up.
 
I've been getting 25 MPH on my 2003 for the past 5 years that I owned it, has the Jaguar 3.9 with a Jaguar Transmission, Head were shaved, Borla Exhaust and K&N filter in the stock housing. When I take trips at 70-75 MPH still the mileage is good, and yes I have a lead foot, cause I love to hear the Exhaust
 
Same size tires? Taller tires require more power to turn, shorter tires cover less road per revolution, thereby changing speedometer input for miles. Either one could show less MPG.
 
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