I have been getting progressively worse gas mileage from my 5.0. I am taking it to a friends shop and we will gut the cats and I also noticed that Motorcraft is making a synthetic blend, so maybe it will make a difference. In town I am getting about 6 to 9 mpg. used to be about 15 mpg.
I will keep you guys updated on the progress if any.

 

Please do!
My truck had been getting REAL bad gas mileage lately as well..

 

I am getting about 10-11mpg in mixed driving with my 95 E150 5.0/E4OD. I got 14mpg on my last highway trip. The previous owner removed all of my purge cannister plumbing, and I believe the EGR is disabled as well. I am not sure if this effects the fuel consumption. Check for O2 sensor codes, mine was bad, although my mileage didn't improve much when I changed it.

 

Well, after a hot west texas day and a few too many beer, I got both cats gutted and the synthetic oil in. I have to say that HP went up dramatically and the sound is great. I have single 3" pipe out the passenger side about 10" before the tire with an 18" glasspack and now 2 hollowed cats. Let me get a good measure of gas in the tank and I will give you guys an update.

 

My 5.8L gets 10 around town, 13-14 highway. Guess that's about as good as I can expect out of this beastly v8. Gotta pay for power.

Just ensure the air filter is good. Neglected/clogged filters cost you mileage big time. When I bought my '93 the air filter quite possibly was the original. Totally filthy. The motor was very hard to start when hot and got at best 9 on the highway. Put a fresh filter in and a noticeable increase in performance and mileage.

 

An exhaust restriction will certainly affect mileage, but it's a SYMPTOM - not a true CAUSE. You need to find out WHY the exhaust became restricted. Disconnected/malfunctioning emissions systems can do a lot of damage, so keep them all working right and they'll only help. The EGR system keeps combustion temps down, so if it's disabled, you can burn holes in the pistons or overheat the cats. Low fuel pressure (due to a dirty filter or bad fuel pump) can also reduce economy, so do ALL the regular recommended maintenance. Tire pressure has a big impact on economy, too, so keep them at the highest comfortable pressure.

For more specific info with dyno tests for each one, read the RESULTS pages of Project MPG.

 

I am seriously going to have to keep my foot out of it to get a good test. I have a K&N filter that was cleaned about a week ago, plugs are about a year old along with the wires. My tires are at 38 psi fall the way around ...Daytona SR 255 70's. CPU throws no codes.

 

do you mean you cutted the whole cat off or just gutted the inside?

 

A properly functioning cat costs very nearly zero HP. All that cutting it off does is increase the amount of crap that we all have to breathe in. As Steve pointed out, if your cat was clogged something caused it and you need to find and fix that problem.

Then put a high-flow cat back on your truck so the rest of us can breathe.

 

Unless you actually had a clogged converter, that mileage is crap for a 302. My 4x4 Supercab 302 would do better than that if I beat the crap out of it all the time.

Unless the mileage return increases, I'd start checking for other things. It could be brakes dragging, U-joints on the way out, or a lot of other things that wouldn't throw a code.

 

I changed the brake pads two years a ago and I always do a "free spin" when I rotate tires and repack bearings. I changed every bearing in the rear end about 6 months ago. The front end may need a mild alignment....the roads out here are chughole crazy. But here is the deal - I drive 95% in town, less than 50 mph for the last four years or so.

Oh and StrangeRanger, I fully expected to give Nancy Pelosi a heart attack, LOL!

 

Poor gas mileage and a clogged cat tells me it's probably running rich.
What do your spark plugs look like?
Is your EFI MAF or S/D?
How many miles on the truck and do you still have the original HEGO sensors?
Is your K&N a drop-in or a complete airbox replacement?

 

From his gallery:

 

Well, the cats weren't clogged up, but now they will never be. It is not running rich and the plugs still look new. The truck has 135k and is all stock. All the sensors and smog stuff is still there....for now.

 

My 83' F-150 5.8L gets around 11mpg town. I guess thats alright for a 5.8L. I think it also has the original filter. That thing is plum filthy. It is black (originally white). I have been meaning to change it. Any suggestions on what new filter will be best. I am thinking K&N.