hey everybody, im new to the forum

I know this question has been asked many times before, but i can't seem to find any clues as to the answer. i have a 302 f-150 efi and it sucks gas like a pig. the only time it's clocked over 10 miles a gallon is when i'm on the freeway. I have replaced all the major engine sensors, spark plugs, wires, cap, rotor, and coil are all new. it also has a new 195 thermostat and 02 sensor. the engine is rebuilt with 50k on it. are there any particular things i can look at into why this truck gets terrible gas mileage?

 

Hello and welcome to the forum.

Considering what you have done already, about the only other things I can think of are: 1) distributor / timing; and 2) fuel injectors / fuel pump. Do you know the history of the engine rebuild? Is it possible that the wrong injectors were somehow installed? Some folks seem to think that if some amount of gas is good LOTS more is better but this is rarely the case. If your injectors or fuel pump are delivering a lot more fuel than the engine needs, you would see very poor gas mileage and probably some black smoke from the tail pipe as well as a lot of soot on the plugs. Sometimes a small change in timing can help or hurt an engine's performance by quite a bit more than seems reasonable. I suppose that this could contribute to poor gas mileage but it would likely also cause the engine to run roughly, back-fire, stutter, etc.

Ed

 

Fuel regulator might be the culprit.

 

well, I have replaced the injectors, with bosche design 3's, they are supposed to be for a stock application, that gives slightly more horsepower without the need of a computer upgrade, and they supposedly have a more efficient nozzle design.

the engine rebuild was actually a swap out for another rebuilt 302, i believe they used the same sensors but i have replaced most of them anyways.

there is one thing to notice, when i start the truck, even with the new plugs, more times then not i will have to floor it to start the engine, and a bunch of white smoke along with the smell of some gas will come out of the tailpipes for a few seconds.

other then that, the truck runs very smoothly, timing is set to 10 degrees, and it's not bad performance wise. but the gas mileage from this little 302 is killing me, i would understand if it was a 460, but it just isn't

thanks for the help,
brian

 

This looks more and more like an uncontrolled fuel delivery problem. There is simply too much gas being delivered to the engine that it does not need. Fuel regulator / fuel pump / computer looks to me to be about all that is left. The engine control computer is usually not an expensive part, if bought used. If you could find a replacement at a junk yard, you could swap it and see if that solves your fuel delivery issue. If not, then the fuel pump or regulator would be my next shot. Is the fuel regulator built into the engine control computer or is it a separate module? I drive an older truck with carb so am not experienced with FI engines.

Ed

 

update,
i have checked the engine codes and fuel pressure regulator, heres what i got,

fuel pressure regulator checks out ok, the vacuum line is dry and the fuel pressure is around 35 at idle and increases to 38 during light throttle.

computer codes: knock sensor out of range, o2 sensor out of range, and egr sensor out of range.

I ran with a stuck thermostat for about 4 months with this o2 sensor, do you think that was enough to make it not read properly??

also, the knock sensor and egr sensors are 2 of the ones i have not replaced, how much do these relate to engine performance and gas mileage?

i also noticed for the first time, a bunch of soot on the ground behind my exhaust pipes, it seems that the white smoke smells like gas, and until my engine gets warm, this smoke persists during light throttle applications when the truck is in the driveway. as well as a stumbly idle at around 500-600, once the engine heats up it settles for a smooth idle around 750-800.

thanks again for the help

 

I've had a similar problem in the past, the truck would never start without having to step on the gas. I thought it was a fuel problem, but I found out that the coolant temp sensor was bad, causing the computer to make the fuel mixture to be really rich. Put in a new sensor, and the problem went away.

 

Other variables to consider proper tire inflation altitude in your area of the country all that and how hard do you drive it?

 

Bedmondo, my new friend..please allow me to ask a few more questions..if I may. Is this a 2w.d. or 4w.d. truck? Standard transmission/automatic or A.O.D.? Have any modifications been made to the "running gear"? Oversize tires etc. etc. Any other changes? While my questions may seem simple it does give the more knowlegable folks here a base to work from to assist you. That being said..I am not a Ford mechanic. Never claimed to be. I am, however, observant. So let me share some thoughts with you. I don't think Ford ever designed the 302 V-8 to be stingy on gasoline. The engine seems to work best at the upper r.p.m. range and at such requires more gas to produce usable horsepower. Rest assured I am not condeming the 302 V-8. It is a remarkably reliable and potent engine...and it uses gas to do so. Life is all about trade-offs. Especially concerning internal-combustion engines. The only way to get more out..is to put more in..simple as that. As well, many things will effect fuel consumption. The first is that rather large flat pedal on the far right-side of the floor-board. I own 1 vehicle that will deliver 12m.p.g. if I "romp" on it and 26m.p.g with courteous use of that pedal. Still another vehicle will yield 45m.p.g. on the Interstate and under 20m.p.g. if I whack the throttle enough in the twisties! Yup..that's a BIG difference in gas milage. Mind you..check out all the possibilities and correct those mechanical problems that need tended to! Then look closely at your driving style and modify them as need be. Not everything is as simple as it seems to be. For example..driving in Overdrive all the time might conserve gasoline..then again..perhaps not! Lugging the engine down actually uses more fuel..not less. Much to think about my friend. Inform these good folks here and they will assist you. YMHS...Audie..the oldfart...

 

this truck is a 4wd, with the AOD transmission. it goes around 2k rpm's at 75. it has 32x11.5x15 tires. the speedo is pretty much dead on in comparison with the traffic radars around here.

and one more update, i replaced the EGR valve position sensor, no more starting issues! no more white smoke, and the truck actually idles lower, around 600 rpm's nice and smooth.

one thing to mention is that it DID NOT like the boshe platinum 4's. I replaced them about a week ago in an attempt to fix this idle issue and i noticed a definite increase in mid throttle power. WOT didn't seem any different, the engine is just smoother.

so i guess now i'm down to the fuel consumption, yes i understand driving habits are a big factor, i'll see how it goes and keep you'll posted, thanks for the help!

 

if all else fails get a vacume gauge(stays in your truck like an oil psi gauge) from the parts house simple install bolt it someplace and run the line to your manifold vacume tree done. watch the gauge wile driving keep the needle up to the highest piont posible for best mpg

 

nevermind about the starting issue, it starts great only once the engine is warm, it still has the issue with cold starting...thought i had it fixed too

 

If you still have the oxygen sensor error code, then that's part of your fuel consumption problem. The engine computer has two modes of operation; open loop, and closed loop.

Open loop is when the oxygen sensor is cold, or not functioning. To fuel the engine, the computer looks at memory tables to make a best "guess" as to how much fuel the engine needs.

When the oxygen sensor warms up enough and is functioning, the computer looks at it for info on how to fuel the engine. It takes real time oxygen content data from the exhaust, and then trims the fuel delivered to the engine for max power and fuel economy, whichever you demand at the time.

If you are getting an oxygen sensor error, you are running in open loop, so your fuel mileage is not going to be as good as it could be.

 

update,

i tested the truck after a nice 15 min drive and it didn't throw the o2 sensor code, instead, i got the ect code 21. my dad says that is a new sensor, anything else that could cause this reading?

 

If you ran the test procedure and the engine coolant was less than 50 degrees or more than 250 degrees, it will throw a code 21.

If you were within temp specs, then take the plug off the sensor and put a meter on the wires. One of them should have 5 volts on it with the key on.

Remember this the engine coolant sensor. And it's the one with two wires going to it. The single wire sensor is for the gauge only.