I’ve got a carbureted 1986 F-150 4x4 (not jacked up) with a 4.9L engine, 4 speed manual tranny, and 3.08 gears in the rear. The truck runs fantastic, absolutely a true solid runner. The problem is, it gets around 12 miles per gallon, usually 10….highway driving. I’m scared to even think about driving in town with it. My ’88 F-150 5.0 with 3.55’s does WAY better, about 10mpg better. I don’t understand, especially with 3.08’s and a 4 speed how my mileage is so low. I’ve heard the 4.9’s aren’t fantastic for mileage, but this is a bit ridiculous! Is there an adjustment I’m missing somewhere? Is there something I need to do to the carburetor? Any help is much appreciated! Thanks!

 

When's the last time it had a tune-up?

 

That sounds about right. A tune up might help, but don't expect much improvement. Your '88 is fuel injected, and fuel injection improved fuel mileage on all engines. That was one of the reasons manufacturers switched over to fuel injection.

Sorry.

Take care,
-Chris

 

Well, it has new plugs, air filter, plug wires, distributor, and ignition coil.
I realize that EFI is better for mileage, but come on, a 4.9 with 3.08's
and a 4 speed manual? What if I had 3.55's and an auto, I'd probably be getting
7-9 miles to the gallon! Would a carb rebuild help any? I just don't think
it should be this bad! What else do you guys mean by tune-up? Maybe I'm missing
something... Is there a mixture setting on this truck I should know of?
Thanks again!



kinf of a P.S. here, but I busted a leaf spring, how hard are they to install? Looking in my Haynes manual it doesn't look to hard..

 

Hi Ford4

I dont recall...is the 4.9L the 300cid..inline 6cyl?? Anyhow...

How are you comparing the mpg?? Before/after new parts?

How old is the carb...thats something i would be looking at.

Has carb. ever been boiled out/rebuilt etc...also dont forget fuel filter...

Is carb adjustable..i dont know on you model..as sometime ago..they started making those carbs. really hard to adjust...fuel/air & maybe idle?...there maybe no visible fuel/air screw to turn. If adjustable..use a vacuum guage to set.

How many miles on that engine....It should get more than 10mpg on hi-way thats for sure. Did you do a compression ck....also use vacuum guage...that guage will tell you alot about carb/motor, etc. Gotta pull so much vacuum like 17# or?...need chart for that.

Lots of reasons why the mpg are off.

Good luck...OT

 

Thanks Old Timer!

That list of things will keep me busy for a little while and hopefully fix the problem! The motor has 140,000 miles on it, and the gas milage is the same with or without all the goodies I put on. I've seen carb. rebuild kits for about $12, so I think I'll get one of those. (Have any idea the level of difficulty in rebuilding one?) I don't think there is an adjustment on the carb., I think it is one of the last years they put carb. on these trucks so it is one without many ***** and switches.


Thanks again!

 

Chances are your carb is a Carter YF, the standby carb for the 4.9L I-6. Rebuild it and you may see MPG go up to about 15. That's about all you'll get out of that engine with that carb...but that's okay for 140K plus. The rebuild is easy, just work in a clean environment and go slowly. If you don't want to rebuild it, pull it off and take it to the parts store and get an exact replacement for it. That should cost about $100 to $150 depending on where you buy it. I've heard you can put a Motorcraft/Autolite 2barrel on this engine, and some even change manifolds and put 4 barrels on them. Don't know what that would do for MPG though. The bad news is your Carter 1 barrel carb will only take about 4-5 rebuilds and then its hopeless...you'll have to replace it. Good news is they generally hold a rebuild for a year or more unless you beat H*** out of 'em. Hope this helps

 

Hi Ford..

Allright...Tm...hit it right on. Interesting... my 77 had the 4.9L...with Carter 1bbl....However, it was adjustable.

Word of caution...man, wish i had ram (memory) like my pc.

Find out what it takes to adjust that carb..set fuel/air and idle. As i recall. rebuilt or new...it has to be adjusted for your engine...i think thats done with specialty equipt...that might involve "propane"? Also, that computer is watching you, but dont think its as sharp as newer 97 to date pcm.

There used to be different type rebuild kits...short/long..meaning short kit had less parts than long. Maybe just one kit now?

Its worth a shot at rebuilding...but really gotta clean that carb. out...boil out usually done by pro. when they rebuild...you can use carb. cleaner..but really spray everything heavy. There used to be carb. cleaner in big can from auto parts...just drop carb/parts in it. really worked good...may or maynot be avail?

Rebuild kit should have instructions...so read & have fun. Oh, if that is original mileage...compression ck. a MUST do. Then again, maybe you dont wanna know.

Good luck...OT

BTW....On trucks etc...Ford first started EFI in 1988....

 

i've rebuilt carbs in my sleep . take it off the truck lay out a towel (white) in a well lit place (table) disassemble it taking note of where the parts came from . use a muffin tin (multiple places to put parts for organizing) to keep parts seperate. you can buy a gallon can of carb cleaner with a basket in it to soak the large parts in .let them soak for 24 hrs . blow all passages out with compressed air . do not stick anything in any where to try to clean . other than wiping out with a rag . carb rebuild kit should come with a diagram of parts and locations and a small measuring stick to calibrate float hieght etc.. take your time and or take pics as you go so you dont forget anything and you should be ok . or you can take the carb off and take it and have someone rebuild it for you . good luck

 

Carburetors used to intimidate me to no end. They were magic boxes, in my mind. Then one day I had no choice but to rebuild one, and was amazed at how easy it was. I have since rebuilt hundreds, and have assembled custom Holley's for dozens of customers. Ray's advice, as usual, is excellent. A good cleaning solution and compressed air, combined with patience, is all you really need. Well, and of course a rebuild kit.

Take care,
-Chris

BTW- 1986 was the first year Ford installed EFI systems in their trucks, but not all of them. 1987 was the year they changed across the board (supposedly).

 

Now that is a compliement unlike anyother , :-) thanx man it means alot

 

Schit, Ray, if I ever decided to set up shop in Texas, you're the first person I'd try and hire.

Take care,
-Chris

P.S. However, under NO CIRCUMSTANCES would my truck be allowed to become the "known good parts truck"!

 

AWWWWWWWW man . lol... that really sux ....lol

 

Don't make me buy locking hood pins...

Take care,
-Chris

 

Well, thanks for Everything guys! This thread has proved to be VERY helpful! There's are several local autoparts stores around here, so I will purchase a rebuild kit and a fuel filter. I do not have a warm garage to work in however, and it's 8 degrees today. So, I won't be able to do this project immediatly, but as soon as it hits 30 degrees I'll be outside working! I'll let you all know how it goes! Thanks again!