Okay here's my thing.in 1993 i purchased a 1992 ford f150 ext cab 4x4 with a 5.0 engine.i drove it all the way until last year when someone pulled in front of my wife and totaled it i replaced it with a awesome looking 1994 ford ext cab 4x4 with the 5.8 351.truck looks new and has un heard of power problem is this thing doesnt get 7 or 8 mpg even on the highway thats with the 4 speed automatic tranny.Now my old truck had the same transmission and the 302 got soooooooooo much better gas milage can anyone tell me what can be causing this surely there isnt this big of a difference in the two motors fuel ecomony?Only Mechanical problems is an exchaust leak and the check engine light is on.Auto zone says light is on because of an egr problem and exchaust leak seems to be coming from flange on right manifold somebody help before i hafta get ridda my truck.........Also one more Question.If my truck is supposed to get this kind of gas milage someone once told me you can change a 351 to a 302 without replacing anything else just motor only because besides the heads they were the same engines is this true?could my 351 be changed to a 302 without coming out a lot of money any help or suggestions is appreciated in advanced..

 

My 1993 BRONCO HAD SAME PROBLEM.
RETREVE CHECK ENGINE CODES .
I REPLACED THROTTLE POSITION SENSOR , OXYGEN SENSOR, AND FUEL PRESSURE REGULATOR.
ENGINE CODE FOR "CAN'T SWITCH TO LEAN AT PART THROTTLE" IS FUEL PRESSURE REGULATOR.
OTHER CODES ARE MORE SPECIFIC.
MOST MANUALS HAVE TEST PROCEDURE FOR THOSE PARTS.
I ALSO CHANGED PLUGS WIRES CAP AND ROTOR.
MILEAGE IMPROVED TO 10 MPG.
THAT WAS TWO YEARS AGO.
LAST MONTH AOD TRANSMISSION WAS OVERHAULED, SLIPPING FORWARD CLUTCH AND BAD TORQUE CONVERTER WERE DIAGNOSED.
GAS MILEAGE IS NOW UP TO ABOUT 12.5 MPG.
I DON'T REALLY EXPECT ANYTHING BETTER.
GOOD LUCK
PWS.

 

I don't think you'd really want to replace the 351 with a 302, you'd be using less motor to pull the same weight. I don't see where that would improve your milage.
I have a '92 ext cab 4X4 long box with the 351 in it, my average milage is about 10-11 for local driving and 14-15 on the highway, I always figured this was pretty good considering my dad has a '95 standard cab 4X4 long box with a 302 and mine gets better milage than his does. When you consider that mine has 190k on it and his has 50k on it I'd say the bigger motor has the advantage. Also, mine can get out of it's own way, his can't. BTW- they both have 3.55 rears.
I have always been a firm believer in going up in engine size for better preformance and economy. Simple logic says more Cubes=more HP=less work=better fuel economy. May not be the most popular way to look at it, but it's always worked for me.

 

I understand your reasoning, but there's more to it than that. Nine times out of ten, in a half-ton pickup truck with all else equal, the 302 will get better mileage then the 351. The 351 is a gas hog...very seldom have I heard anyone mention getting 14-15 mpg with it and it's usually around 10-12 mpg. With the 302, the average is around 14-16 with some reports as high as 18-20 mpg. While there may be some anamolies, and engines that need tuneups or other mechanical work shouldn't be considered as they scew the averages, this tends to be what I've read and heard over the last several years.

With that said, I plan on swapping my 302 for a 351. I'll trade more power for a couple mpg's. As long as I'm at or close to 10 mpg, I'll be happy! daniel3312, wanna trade ?

 

It is a thirsty engine, almost as bad as 460, which gets in single-digits in town and towing, and 11 empty in my experience.

Nevertheless, you should be doing better than that. How many miles on it?

Big MPG reducers are :

Bad O2 sensor, going bad slowly after 80,000 miles

EGR valve

Coil, plug wires, spark plugs - check compression?

Timing, knock sensor

Bad catalytic converter can also cause poor performance and MPG

Alignment, tire pressure

 

My truck has 139,000 on it autozone says the check engine light is due to an egr problem.u can let it idle for a week it will never come on but the second you start driving it pops on!Has anyone here ever did a swap from a 351W to a 302 in a f150?there's been alot of debate from people ive talked to some says it can be done without changing anything but the engine others say its next to impossible???????????????I'll have to get you guys a pic of this truck because body wise it looks as if it just rolled from the assembly line and has alot of features still considered as options even on the 04 models.with a good tune up the 92 i had would get 20mpg on the highway with the 302 thats why i wasnt scared to get this one with the 351 i figured based on the 302 it couldnt be to awful much worse on fuel but boy was i wrong!If it can be done fairly easy im sure i'll swap this engine out so anyone who may have any info on the swap will be appreciated.


Daniel

 

I would run the diagnostics on it and make sure everything is ok including the EGR. The reason you can idle and the light not come on is because the egr only opens under part throttle.

My 93 351 4x4 206000 miles extended cab gets 15-16.5 mpg

 

I have a 1990 Bronco EB 351W I have K&N cone filter new plugs wires ect and I get 10-13 mpg I am hopeing duel exhaust will help this

 

Fix your egr valve! Odds are, the valve isn't opening when it should, which is why the MIL comes on. If the EGR doesn't open, you'll run rich, and will get crappy gas mileage.

Fix the egr.

 

When I first registred i was strongly considering changing to a 302 engine but after reading the post here on the 351 and went to ebay looking at the different mods for the 351 and what really topped it off is when i drove my dads 93 with the 302 and realized the big power difference in the two engines it was mind blowing Once i really investigated the problem i realized my egr problem was a simple vacum line off the truck causing a serious leak once fixing it the check engine light was gone and my gas mileage is up to around 17 mpg on the highway when i keep my foot out of it thanks for all the help and tips it saved me alotta money and lots of headaches!But i have one problem and my truck will be in perfect mechanical condition.......my right exhaust manifold is leaking right on the connection to the pipe and any ford lover knows that instead of doughnut gasket ford uses a flange made onto the manifold.the studs seem to be as tight as they can possibly be i know this because i attempted to tighten them.Is there any other suggestion to stop this leak???

Thanks Guys

Daniel

 

If it was the vacuum line going to the EGR that was off, it wasn't a vacuum leak that was causing your problems, it was an inoperable EGR valve.

Try loosening the exhaust and it's hangers, and then retighten evenly.