Very Bad Gas Mileage, But It Has Many Performance Parts.

[blackfox91]

As I said in the title my gas mileage is unusually low. The mustang has a few aftermarket performance upgrades. like a Holley electric fuel pump. a performance camshaft and a Holley 660 CFM carb, shorty headers and an off-road X-pipe. is it possible that the carburetor and fuel pump just need adjustment? My mechanic said that it is a very aggressive carb and fuel system and that it's required to run the engine properly. he also said something about secondaries but I want a second opinion I think he's jumping to conclusions because 6mpg is absolutely ridiculous.

 

[RaggedGT]

I have a few questions,
was the car converted to carb?
Does it have a fuel pressure regulator?
What intake is on it?
Are you running a carb spacer?
Have you verified timing?
Checked/read the plugs?
Do you have a AFR gauge?
Does it smell like raw fuel?
Do you know the cam specs?
What rear gears are in it?
Auto or 5-speed?

Honestly I am nowhere near a carb authority,but I know a couple guys that are- @madmike1157 @Boosted92LX @Davedacarpainter @90sickfox
Maybe they will pop in with some answers

 

[blackfox91]

I have a few questions,
was the car converted to carb?
Does it have a fuel pressure regulator?
What intake is on it?
Are you running a carb spacer?
Have you verified timing?
Checked/read the plugs?
Do you have a AFR gauge?
Does it smell like raw fuel?
Do you know the cam specs?
What rear gears are in it?
Auto or 5-speed?

Honestly I am nowhere near a carb authority,but I know a couple guys that are- @madmike1157 @Boosted92LX @Davedacarpainter
Maybe they will pop in with some answers

was the car converted to carb? Yes
Does it have a fuel pressure regulator? Idk I think it does.
What intake is on it? it says "edlebrock"
Are you running a carb spacer? Idk
Have you verified timing? not yet I night a timing light
Checked/read the plugs? not yet
Do you have a AFR gauge? no
Does it smell like raw fuel? yes
Do you know the cam specs? no how can I check that?
What rear gears are in it? idk
Auto or 5-speed? 5-speed

I am gonna need to more closley inspect the car for you

 

[RaggedGT]

was the car converted to carb? Yes
Does it have a fuel pressure regulator? Idk I think it does.
What intake is on it? it says "edlebrock"
Are you running a carb spacer? Idk
Have you verified timing? not yet I night a timing light
Checked/read the plugs? not yet
Do you have a AFR gauge? no
Does it smell like raw fuel? yes
Do you know the cam specs? no how can I check that?
What rear gears are in it? idk
Auto or 5-speed? 5-speed

I am gonna need to more closley inspect the car for you

The more info you can provide,the better answers/suggestions you will get
I'm guessing you got the car the way it is?
If so would you be able to contact who assembled the motor?

 

[Davedacarpainter]

Yeah, what Chris says. More info is good.

6mpg sucks very bad. You have issues.

The gas smell in the exhaust obviously means it's running rich.

Carb probably has too large of jets.

I'm fairly convinced your mechanic may be an idiot.

To have that kind of mpg, it would have to be pretty a badass engine.

Where did you get the car from? Anyone that can tell you the modifications to it?

At least post a picture of the engine so we can get an idea. I want to see if you have new heads to go with the cam and intake.

A 660cfm carb isn't necessarily too much, though it is about the limit for a mildly modified engine.

If you can, come up with a parts list of what has been done to the engine and drivetrain. There are just too many variables and we need to see and know as much as you can get us.

 

[90sickfox]

6 mpg is ridiculous. With a 650 cfm carb ( tuned correctly ) I got 26mpg...with a mild cam, ported heads, and a big foot.

It depends a lot on your set up....and rear gear ratio.

 

[Jersey Joe]

My V-10 super duty gets twice that, you definitely have an issue.

 

[blackfox91]

I tried to contact the previous owner. I couldn't get a hold of him. I am gonna check everything and get back to you guys on my next day off of work (this Monday). I am determined to figure this out because I can't afford 80 a week in gas.

 

[Davedacarpainter]

Include the model number of your fuel pump, I'm assuming it's an external one, and you'll be able to find it. If it is inside the tank, you will have a fuel pressure regulator somewhere. You might have an fpr even for an external pump. It should be up by the right hand side shock tower area. If you find it, tell us what're model is and what the pressure is set at.

 

[blackfox91]

Include the model number of your fuel pump, I'm assuming it's an external one, and you'll be able to find it. If it is inside the tank, you will have a fuel pressure regulator somewhere. You might have an fpr even for an external pump. It should be up by the right hand side shock tower area. If you find it, tell us what're model is and what the pressure is set at.

Yes this is an external electric fuel pump from holley, unfortunately I work all day. I will have a day off on monday and I will update this thread. I may also drop the tank just to make sure there isn't anything wrong in the back and I will be doing various other small jobs on this car. At this point I have no idea what's causing it, but this car has LOTS of problems. I also have a gauge that tells me the fuel pressure. I will be posting a pic of the engine soon.

 

[General karthief]

I guessing by your name it's a 91, lots of issues when people convert to carb, two things I would start with, and I mention this only because the 'mechanic' said something about secondaies, start the car and while its idling, carefully look into the back two holes of the carb with a light, sometimes they bleed fuel, carb may need to be rebuilt, another thing that would be interesting to know is if the purge canister is functional.

 

[Gear grabber]

6 mpg,something is very wrong.

Earlier this spring,i did a mpg test on my car. Dart 427,Holley HP 1000,ported super vic.
No vac advance,5 speed (at the time) 4.10 gear. At a steady GPS 65,managed just over 19 mpg.

You will need to start with the basics. Ignition timing,fuel pressure,float hight
primary and secondary jetting,air bleeds (if it has them)

Find out what model carb you have,and all the factory settings.
And compare to what you have now.