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Poor gas mileage

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Livermore, CA, USA
#1
I recently picked up an ST with 127k miles on it. I am getting about 25 mpg with mostly highway driving. That seems quite poor. I checked the tire pressure and it was fine. What should I check next? Spark plugs? Air filter?
 


slopoke

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#2
Wow, that's kinda on the low side. I was getting upper 20's and lower 30's commuting to SFO. Keep an eye on oil consumption and maybe do a compression test. I'm in Livermore as well.
 


TyphoonFiST

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#3
Did the vehicle some with a Cobb Accessport? Also....O2 sensors should be replaced every 75k as preventive Maitenence....in doing so your mileage will definitely go up some*

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Valleyfield, QC, Canada
#4
I'm having a similar problem and I thought I'd post it here instead of making a new thread...

I bought a Dizzy Pop Tune right before winter and ever since I've been getting pretty bad mpg, do tunes have a big effect? I had an Cobb OTS 91 before and it was fine
Another factor that comes to mind is winter, Where I am from our winters are around -30°C (-22°F 14°F ) Does any one else get a big difference in mpg during cold seasons?

To give an example, with my tune and cold weather, I lose around 80 miles of range per tank, that's a lot considering the tank is so small.. Anyone else have this?
 


XR650R

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#5
I'm having a similar problem and I thought I'd post it here instead of making a new thread...

I bought a Dizzy Pop Tune right before winter and ever since I've been getting pretty bad mpg, do tunes have a big effect? I had an Cobb OTS 91 before and it was fine
Another factor that comes to mind is winter, Where I am from our winters are around -30°C (-22°F 14°F ) Does any one else get a big difference in mpg during cold seasons?

To give an example, with my tune and cold weather, I lose around 80 miles of range per tank, that's a lot considering the tank is so small.. Anyone else have this?
Mileage definitely goes down when it's that cold. Pop tunes get the pops from burning fuel. Try going back to the Cobb tune and see if it improves.
 


XR650R

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#7
I recently picked up an ST with 127k miles on it. I am getting about 25 mpg with mostly highway driving. That seems quite poor. I checked the tire pressure and it was fine. What should I check next? Spark plugs? Air filter?
I would definitely check the plugs and filter. Check your emissions hoses and boost hoses and all the easy stuff. Change the air cabin filter, too. I bet it's filthy.
As already mentioned, cars will burn more fuel when it's cold out. Just the nature of internal combustion engines.
Do you have an access port? It's possible someone put a tune on it, then sold all the stuff separately when they sold the car, but left the tune.
A car with that many kms on it may have other issues, but start with the easy stuff.
 


OP
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Thread Starter #8
I checked the air filter and it was fine. It's been warm out here so I don't think it is the weather. I am going to ask the previous owner if he put a tune on the car. I don't have an access port. I guess thing I am going to check is the plugs, then a compression test.
 


OP
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Thread Starter #9
Wow, that's kinda on the low side. I was getting upper 20's and lower 30's commuting to SFO. Keep an eye on oil consumption and maybe do a compression test. I'm in Livermore as well.
Do you know of a place I can get a compression test done? I think I can rent a compression tester from a auto parts store, but I haven't done it before. I assume it's not too difficult.

Also, if you have an access port that I could borrow to run some diagnostics that would be great.
 


TyphoonFiST

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#10
Do you know of a place I can get a compression test done? I think I can rent a compression tester from a auto parts store, but I haven't done it before. I assume it's not too difficult.
Any Fomoco dealer can use their dealer IDS scantool to do a compression check and injector flow check. FYI....or you can buy your own Compression checker and do it yourself.

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green_henry

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#11
If you're not buying Top Tier, it would be interesting to know if you see any improvement by doing so. Higher amounts of ethanol will also hurt mileage, so maybe it's just CA's winter blend?
 


TyphoonFiST

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#12
If you're not buying Top Tier, it would be interesting to know if you see any improvement by doing so. Higher amounts of ethanol will also hurt mileage, so maybe it's just CA's winter blend?
And California does do a winter blend....believe it or don't!

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slopoke

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#14
Do you know of a place I can get a compression test done? I think I can rent a compression tester from a auto parts store, but I haven't done it before. I assume it's not too difficult.

Also, if you have an access port that I could borrow to run some diagnostics that would be great.

Compression testers are relatively inexpensive and easy to use. Just install it, crank it a few seconds, then read the pressure gauge. Write down the pressures and see if they are close to one another.

I don't have an accessport anymore, since I sold my Fiesta last year. You can get a code scanner for under $100.00 and it's something you should have anyhow.
 


OP
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Thread Starter #15
I did a compression test and replaced the spark plugs. The thing is that the compression test showed each cylinder at around ~1200 kPa or 175 psi, which is about a 12:1 compression ratio. I was by myself so I had to turn the engine over and then get out to look at the gauge. It didn't really move down so I think I got an accurate reading.

I am really puzzled that the reading is high. Could it be that there is a tune on the car from the previous owner that was not removed?
 


Ford ST

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#17
I'm going to give you a suggestion you have an engine that has some miles on it your fuel injectors are probably not flowing as good as they could. I definitely recommend using a high quality fuel injector cleaner.



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