OK, my 2000 f150 with the 5.4 4x4 is getting 10mpg. I know that's crazy low since I drive 80% Highway. Stock ride height, stock size tires, 265/70/17 running 35psi, I baby it a majority of the time. Don't have any cel codes, minus the 02 sensor.

Things wrong with my truck: exhaust leak at the passenger manifold, no cats. I know it should still be better than 10mpg.

Any tips on fixing the manifold? It's my only vehicle and I'd like to get it done in one day or less.

 

It is probably running extremly rich due the exhaust leak along with bad oxygen sensors.

 

Wouldn't that make it run lean?

 

1. Replace the manifold if its cracked. Careful with the bolts, they break off in the head easily. Soak them with PB blaster the day before you pull them.

2. Replace your front o2's if bad

3. Get a tuner (SCT from MPT includes custom tunes) and disconnect rear o2's if you have no cats. They can make a custom tune for the deleted o2's.

Guaranteed you'll pick up 3-5 mpgs at a minimum.

Also, your current issues will cause it to run rich. Listen to carcrazygts2. Dude is solid.

 

No because under load a exhaust leak will create a vacuum and suck fresh air making the PCM think that there is more oxygen in the system that there actually is. So the PCM adds fuel.

 

Ah. Thanks for explaining.

I'm actually considering having a shop fix the mani leak. I know it's just the gasket as I've seen a chunk of it hanging out when I had it up on the lift at work. I just don't want to break a bolt off in the head and screw myself. Shop rates are around 230 bucks a side.

 

Depending on the condition of the exhaust studs you may have to replace them. Ive seem them rusty and snapped before a wrench ever hit it.

 

I'd get a shop to do the manifolds. It's a bastard job most of the time and I'd rather someone else do it honestly because it downright sucks.