81 ford f-150 4x4 - starts good, runs erratic

ford

#1

300 cu. in. 6 cylinder, 4 speed manual trans; starts normal but runs erratic; stalls out after short period of time; have replaced spark plugs, plug wires, rotor, distributor cap, fuel filter; there is no white foam on the dipstick so I don?t think there is a blown head gasket; ran normally last fall; sat much of the winter; started driving again in spring; starts good but runs erratic; will stall out if I try to drive it.


#2

So you start it up and it runs fine for a while but then acts up or does it always idle fine, but cuts out when you accellerate or put it in gear?

What’s the carburetor doing? Is the choke opening properly? Is the accellerator pump working properly? Have you checked the float level lately? Have you checked the fuel pump flow?


#3

Disconnect the vacuum advance and see if it still stalls. If it doesn’t stall, check for frayed wires on the ignition pickup. If it still stalls, the huge ignition module may be going. It’s back above the master cylinder on some Fords. The parts place may ask if it is a blue grommet or black grommet module. They are talking about the rubber where the wires come out of it. They all look black until you check the underside when it is unbolted. You may have to try cleaning the grommet. It is usually blue.


#4

Aside from the other advice, check the EGR valve; It may be sticking. Had this problem with my 77 F-150 Supercab.


#5

Sounds like a carburetor problem to me. Does it idle fine or ragged?
If it idles fine but falls flat when you try to accelerate then this would point to a carburetor accelerator pump problem. (carb overhaul in a nutshell)


#6

Dear GJ:
It runs rough right away. The carb, i found, has never been rebuilt. That is probably the first step. Do you know what the fuel pump pressure needs to be on these old fords?
Thanks for your assistance.
Dennis from MN


#7

Dear Newpony:
Thanks for your assistance. I think I will be rebuilding the carb as a first start, miles are relatively low, but it is getting old.
Dennis from MN


#8

Dear PDV:
The pickup is up north, next weekend when I go up I will disconnect the vac advance and see what happens. The vehicle still has the original module. Do you know if this pickup is known for going through modules?
Thanks for your assisance.
Dennis from MN


#9

On a carbureted car, the fuel pressure isn’t that important since all it needs to do is get the fuel into the fuel bowl. A few PSI is fine. What is important is how much fuel the thing pumps-- a weak pump or clogged filter will cause not enough fuel to get to the bowl and it’ll run empty during prolonged acceleration.

But that doesn’t sound like what’s going on here. A carb rebuild will likely fix it.