Fox Xtremely high fuel consumption

[PonyGTrider]

Hi all,
I must post this new one because I really don’t know what’s goin on.
My MPG are pathetic at the best, getting 9.5 or less miles to the gallon is unsustainable!
This post will be long since I’ll describe my specs and the things I’ve already looked into:
Engine 306 with 170 twisted wedge heads, flat top pistons TFS upper and lower intakes, TFS stage 1 cam, sparkplugs set at 0.054” and don’t see any dark stuff on them, 65mm TB, 19 lb injectors with no leaks, stock regulator with no leaks and pressure at 39lb vacuum on, brand new O2 sensors, stock 55mm MAF tube and stock sensor, 210lph fuel pump, rear end fitted with 3.55 gears, T5 Z specs with the right gear for the 3.55 rear gears and shifting at 2.5 k, cobra disc brakes with no pads rubbing, all four 245 45 17 tires inflated at 36psi, front cobra brake discs with no pads rubbing.

Sooo, with all of that information what in hell is going on with this horrible fuel economy???? Anyone has any idea what could be the problem???

I haven’t had any chance to buy an AFR gauge to monitor my air fuel mixture, but no matter what driving style I do the problem still there.
I don’t see any black smoke even at high rpm and the car is used mostly city driving.
I have an A9L and a A9P computers both in good condition but the problem still there…

Does anyone have any idea about this?

I truly appreciate any help on this issue, kind of desperate….

Thank you all

 

[86HO5.0]

Codes? Any tuning been done?

I'd recommend a larger MAF and injectors at some point as well. That 55mm MAF is choking that engine, the 19lb injectors won't be happy once it's allowed to breath.

9.5mpg is terrible. I average 18-20 driving with a lead foot.

 

[PonyGTrider]

No tune has been done and I don’t see that coming soon no places to tune where I live.
I’ve already tried a 95 mustang GT 70mm MAF tube and electronics which wre running with 19lb injectors, same high fuel consumption.

No error codes from the ECU, everything looks working fine but obviously that horrible mpg tells me otherwise.

Thank you for your ideas

 

[86HO5.0]

Have you tested the ECT? I wonder if it's stuck in warmup enrichment.

A wideband would be a good idea.

 

[PonyGTrider]

Have you tested the ECT? I wonder if it's stuck in warmup enrichment.

A wideband would be a good idea.

Yes I’ve checked both the ECT and the ACT sensors and they change their resistance accordingly with the temperature as expected on the charts.

Definitely AFR monitoring should lead me to something more consistent

Thank you

 

[gkomo]

Catalytic converters or off road exhaust?

 

[KRUISR]

How is it running? My first thought was stuck or dirty injector, but I would expect some kind of poor running condition if this was the case.

 

[Blackhawkxx]

Does your oil smell of gasoline or at a higher level than it should be?

 

[nickyb]

With the price of gas maybe someone is siphoning some of yours.
Short story on that, an older guy told me his neighbor bought a new VW battle back in the sixties,said it was going to get great mileage, so him and another neighbor put a gallon or two and never other day. When he bragged how great the mileage was,the next couple of weeks they siphoned some out. Drove that poor guy crazy.

 

[PonyGTrider]

Catalytic converters or off road exhaust?

I removed the secondary cats, the upper ones still there and in good condition.

Thank you

 

[PonyGTrider]

With the price of gas maybe someone is siphoning some of yours.
Short story on that, an older guy told me his neighbor bought a new VW battle back in the sixties,said it was going to get great mileage, so him and another neighbor put a gallon or two and never other day. When he bragged how great the mileage was,the next couple of weeks they siphoned some out. Drove that poor guy crazy.

Not a chance, my ride stays in a closed garage.

Thank you

 

[PonyGTrider]

Does your oil smell of gasoline or at a higher level than it should be?

No fuel in the oil and the level stays the same all the time.
I can imagine having four or five gallons in the oil pan.
But no, there is no fuel smell in there.

Thank you

 

[PonyGTrider]

How is it running? My first thought was stuck or dirty injector, but I would expect some kind of poor running condition if this was the case.

Since I have. TFS stage 1 cam it idles really nice. And it accelerates very nice pulling really strong from 2K rpm with no misfire.
I’m really frustrated! Where does the fuel’s going? No leaks from the fuel tank and charcoal canister is holding the fuel vapors from the tank and venting them to the upper manifold thru the purge solenoid valve improving the fuel economy…. Ha!!!!!! Well no fuel saving here!!!!
Also the fuel return line is free no blockings.
So what else???

Thank you

 

[AeroCoupe]

Just me but with those heads, intakes, and cam you really should be running a 70mm MAF “calibrated” to some 24 or 30 lb/hr injectors. Not meant to solve your mph issues just saying you are leaving hp on the table.

A tune would be the best but being you are in Mexico your best bet is a remote tune. You can most likely get an SCT chip and some software and the. Have someone from here in the US get online with you and tune it. Would start with a base tune and then data log so they can make changes.

You really need a wide band AFR as this is the only way you are really going to know what is going on. What type of fuel are you running? The more ethanol that is in it the worse the mileage will be.

 

[PonyGTrider]

Just me but with those heads, intakes, and cam you really should be running a 70mm MAF “calibrated” to some 24 or 30 lb/hr injectors. Not meant to solve your mph issues just saying you are leaving hp on the table.

A tune would be the best but being you are in Mexico your best bet is a remote tune. You can most likely get an SCT chip and some software and the. Have someone from here in the US get online with you and tune it. Would start with a base tune and then data log so they can make changes.

You really need a wide band AFR as this is the only way you are really going to know what is going on. What type of fuel are you running? The more ethanol that is in it the worse the mileage will be.

I had just running a 70mm MAF tube and sensor from 94-95 mustang GT with the same 19lb injectors. Now I have the 55mm stock MAF to see if I see any difference. My battery is disconnected so I will start from scratch.

I didn’t know you can get that type of remote running so I will look into it.
I run 87 octane gas and never got any knocking even with over 16 degrees of advance.

I will try to get a wide band O2 sensor and an AFR gauge, with that I have to be able to notice any rich condition that is hurting my fuel economy. The strange thing is that if the engine was running overly rich I see no black smoke and the plugs aren’t black…

Thank you

 

[General karthief]

How are you calculating MPG?

 

[PonyGTrider]

How are you calculating MPG?

Fill up tank and write down how much fuel went in, zero the trip button, take reading of the odometer, and drive until about 1/4 of a tank is left.
Refill the tank write down how much fuel went in and calculate how much fuel was spent and divide by the driven miles from the previous odometer readings

Repeat all the previous steps two or three times all done from the same pump then average all the results

 

[bird_dog0347]

Are you certain that your speed readings are correct with the trans/rear end combo? If the speed is off so is the miles traveled and thus your MPG could be wrong as well.

Also, was the MPG better before and if so what changed?

 

[AeroCoupe]

Gear Ratio Calculator

Speedometer Gear Calculator

5speeds.com

 

[PonyGTrider]

Are you certain that your speed readings are correct with the trans/rear end combo? If the speed is off so is the miles traveled and thus your MPG could be wrong as well.

Also, was the MPG better before and if so what changed?

100%, I even compare my speeds with different satelicaldevices and it is right on the spot

Gear Ratio Calculator

Speedometer Gear Calculator

5speeds.com

My set up is calibrated properly and my speed is accurate.

Thank you