majormini

Basic specs:
1979 F-150 XLT
351M
4x4

Summary of problem:
Just replaced fuel pump b/c engine would intermittently die while driving at speeds over 50 mph (would not want to sustain high speeds) or during heavy acceleration. I though it was a bad fuel pump, hence I replaced it. Fuel filter in front of the carb was black, so I just replaced that as well. Swapped out the fuel line to the carb from the pump, used the same 5/16'' line that was previously on it (I'm a 2nd owner). Just test drove it again today, it didn't go 60 mph for more than 1/2 mile before engine acted like it wasn't getting enough gas and a few seconds later cut off entirely--I lost power steering, brakes, etc. Came to a stop, cut it back on, and off I went--under 50 mph... What's the deal? The fuel filter isn't dirty yet, so I doubt it's a rusty tank. Are my fuel lines big enough? It is a carb issue (see below)? PLEASE HELP!!! I love my truck!

Other problem (possibly related?): Does not want to idle at a single speed while still cool. Will idle at 750ish rpms once it's good and warm, but generally starts up at 1500 rpms. I can punch the gas and it settles a bit, but not until very warm will it idle around 750. I have also recently reset the timing to 0. It was around 20 before..

Other possibly helpful information: Spark plugs are basically new, does leak a tiny bit of oil from the plug on the pan, but I check the level frequently to make sure there's enough oil, has a 7'' or so lift with 34'' (guestimate) oversize tires, even with a steering stabilizer it wants to wander a bit, engine is VERY strong and smooth (under 50 mph), no knocking, no noise...


Thanks for any help--
Happy Independence Day!

kdbenton

You have gunk in your tank.... and I would bet if you pulled the sending unit you would find the sock filter on the pickup tube is as black as the filter you checked was.

Time to drop the tank and have a look at the sender/pickup tube.

planehunter

IMO you have possibly a couple of problems. Your fuel lines are big enough but I think you are sucking air at one of your fuel line connections between the carb and tank. If you have dual tanks you multiply the problem. You should replace any line that has brittleness or the signs of cracks if you try to bend it into a 90'. Another problem could be debris in your fuel bowl on the carb. When was the last carb rebuild? I don't know what factory timing is but I don't think it's 0. Reset to factory specs. What condition is the rest of the ignition, cap, rotor, wires, etc?

majormini

Thanks for the replies, guys!
No dual tanks and I don't know when the carb was looked at last.. Definitely taking that to a pro, though. Distributor cap and rotor are beautiful

planehunter

Keep us up to date on what you do and the results.

majormini

Ok here's the update. Mechanic said the problem was definitely the sender. The strainer was torn and cracked, so it was sucking air and wouldn't reach to the bottom of the tank. You guys are good. Thanks again for the help!

WarDawg45

Indeed. I had this same issue with the same symptoms you describe. I dropped my tank (not as bad as it sounds) and yanked the sender. My sock was loaded with garbage and the tank was worthless. I put a plastic tank from Jeffs Bronco Graveyard on it but if you do this MAKE SURE you get a vented cap otherwise it will vapor lock.

SEARCHING

i have the same fuel starvation problems . I have dropped the tank , new sending unit , new fuel pump, new fuel lines, new fuel filter, rebuilt carb. Now what ?

manicmechanic007

That fast idle when cold is what it is supposed to do (after warmup of about 2 minutes, you can kick it down)
Otherwise, it will die out cold
There is a fast idle adjustment screw on the passenger side of the carb to adjust the fast idle speed
Those of you with carbs should learn about them yourselves and learn to rebuild them and some theory
Not many of us techs left who know anything about carbs and I am not rebuilding yours
They used to call it (put a kit in it) and that does solve a bunch of issues
You really need to learn about choke pulloff measurements and the vacuum break, also the trans kickdown adjustment and float level adjustments
Then you will be more expert than most and will get a man card stamp for any successful carb repair you make
Good luck

SEARCHING

There are three canisters on this 1979 ford f 250 with a 460 , 2 wheel drive .
1. Do they get old and go bad ?
2. What are their purposes in the smog fuel process ? What is the third canister further down .?
Multiple vacuum hoses .
3. Where do you purchase ?
How can you tell if they are bad .?
The glass filter was showing air bubbles ,after tank drop, new sending unit, new fuel lines, carb rebuild .
Please help
searching