i have a 1994 f-150 with a 351-w in it. When I start it, the choke comes on until it warms up, but this time the choke didn't come on,& it started to idle & was rough running. I notice the black smoke was heavy coming out of the pipe.
Trying to figure out if there is a choke solenoid that needs to be replaced or? The truck has only 128,000 original miles on it. Can someone help, thanks.

 

Maybe we can offer a suggestion or two.

Pretty sure your vehicle has fuel injection which is easier to diagnose than a carburetor.

Anyway, if you know or can identify the fuel pressure regulator on the engine it has a vacuum hose connected to it. It is located on the driver's side top of the fuel rail about in the center of the engine. That regulator controls the fuel pressure sent to the injectors. It has a diaphram inside and is operated by manifold vacuum. If that diaphram gets ruptured it allows the manifold vacuum to pull in all the fuel it can and that results in a very rich running engine that has no problem producing black smoke.
What you can do is pull that vacuum hose off and see if any fuel drips out.. If it does the regulator must be replaced. May require an allen wrench to undo the little bolts that secure it to the fuel rail. Remove the bolts and install the new pressure regulator. It is that simple. Let us knowhow you make out with this ,OK , thanks.

Most auto supply stores will have one, NAPA, Advance, O Reillys etc.

 

hankey, thanks for the info. I pulled the hose, but no fuel. I hooked up my vacuum tester to see if it was ok. I pulled 15inches of vacuum & did not bleed off. Started the truck up with the tester on, but no change. I did test the egr valve
diaphram, as soon as i pulled a vacuum on it, the engine almost died. When the truck is cold,the choke comes on & high idle until it's warm. Now it just idles and struggles. When i hit the gas, black smoke comes out & leaves black soot on
the ground. Not sure which way to turn. Do you have any ideas? Thanks.

 

Another thing you might check, If the air filter is restricted , the engine can't get enough air and will run rich.

The air/fuel mixture when cold is controlled by the pre-programming in the ECM.until the oxygen sensor heats up and allows fuel control by conditions.

If unmeasured air is getting into the combustion chamber the oxygen sensor sends that info to the computer and it responds to what it perceives as a lean mixture and adds more fuel to compensate.
This fuel addl fuel is not necessary and now we have a too much fuel condition that produces black smoke and poor fuel mileage aside from poor performance.

You might look for a PCV system hose leak or PCV valve sticking open..

 

Hanky, thanks again, but no change. I did pull the pcv valve (fun ), wasn't bad, cleaned it out, put it back in ( lots of fun ) but no change. Trying to figure out
why when it starts up, the choke is on, but still idles at low speed, causing it to blow black smoke when i hit the gas .Is there a solenoid that operates the idle
to high when the engine is cold until it warms up? I have a obd ii reader, but this has a EEC TEST port in the engine compartment but don't know what can fit it.
Any more ideas to help out?

 

A little FYI,
With fuel injection,there is no choke.. The system in your vehicle is referred to as OBD I.
`Any and all tests need to be made at the components. OBD (On `Board Diagnostics) OBD II provided a lot more info to assist with diagnosis.
`I suggested some things to check, don't know if you did them or not. Air filter, large vacuum leaks etc.

Does the engine run rough and smoke whether cold or hot?
If so, suspect an injector problem of excessive fuel pressure . `The only way to verify this is to check fuel pressure with a special gauge to connect to the fuel rail. Some auto stores will rent that gauge , worth checking .Until we have some idea of what is going on , we can keep replacing good parts and that can get disappointing and expensive. Can you do this ?

 

hanky,
now it doesn't matter if it cold or hot, still blows black smoke when i hit the gas. When i tried to drive it to get it hot, it would snap my neck when it would shift gears. Still trying to figure out why it idles so low when its cold.

 

If all the passages are possibly full of carbon,it might be a good idea to check if the idle air control valve is capable of functioning properly. Did anybody check that part?