I guess I just don't understand how the fuel pump can be working but only pumping air. Is this possible?

 

The same way any other pump might run and pump nothing, don't over analyze it too much. No different than a little water pump for a Jacuzzi.
It might run ok but if there is no water to prime it, won't pump anything.
It won't run that way long though, you're not doing it any favors running it dry.
I would be sure you are getting fuel to it first.

 

Robert when you say you cycled the key, did you leave it on till the fuel pump quit running or did you just cut it on and off. Cycle takes 20-30 seconds per key turn. 3-4 key turns. Be careful you don't discharge your batteries. That leads to another whole mess of problems.

What about the fuel cut-off under the passenger seat. Did you check that?

 

I ran complete cycles numerous times and still nothing but air pumping through. Yes I checked the cut off as well ...passenger side kick plate....it was fine.. OK so the fuel pump is in the frame rail in the filter housing so if something in the tank is blocking fuel from getting to this point would it pump air. Might my pickup line be totally blocked inside the tank?

 

If you almost ran it out of fuel, yes it probably picked up trash in tank. Before I dropped tank I would go back over filter change. Check WIF drain plug make sure "O" rings are in place. Check main fuel filter and make sure cap is not cracked, check "O" ring on cap that it is in place and not broke, mashed or twisted.

 

Might my fuel pump be malfunctioning by only pumping out and not drawing fuel in?

 

On a previous post you said it was pumping some but when it burnt off the fuel in the bowl it quit running. I'm thinking air being pulled from somewhere. You said it bubbled in the bowl. Like I said I would back track at where my problem started and go from there.

 

No cracks in the cap. No fuel at all at this location either. Bad pump or blocked pick up line? Is it possible to clear the pickup line without dropping the tank? Would it be safe to blow air backward through the line and clear it this way?

 

I think there is a one way valve in the line, but somebody else needs to answer that because I'm not sure.

 

I think Tideman makes an excellent point: go back over what you did before this started. Because it ran, but just not good below 1500rpm, prior to doing the fuel filters. Since it ran "good" at higher rpms (a problem possibly masked), your HFCM was putting up plenty of fuel just prior to doing the filters.

Take the lower filter out again, when you open the drain does it drain a good amount (like it did the first time)? Now, again what brand filter did you use? Inspect it for defects, make sure it gets snapped into the cap, make sure the o-ring is lubed and inspect it for damage. Get a mirror and flashlight and look inside the HFCM for signs of rust and crud.

If it wasn't a Motorcraft or Racor filter kit I'd go so far as replacing the filter. Take your time and make sure the cap seats completely and don't over tighten it. It will get harder to turn once the o-ring hits the case, so keep turning till the cap shoulder bottoms against the case.

I'd probably do my 1st prime with the upper bowl cap off and someone else at the key.

Let us know if there is anything else you might thought was insignificant to tell us. Do I have the events/symptoms correct?

 

Yes you do. Motorcraft filters. Upon taking the lower cap off there is no fuel at this point.

 

So we have narrowed it to 2 possible causes. Either my pump is bad or my pickup line is blocked. Well I'm going with the easy choice first...I will replace the pump. Let's cross our fingers!! The tank is 3/4 full.

 

And you are getting bubbles in the upper fuel bowl, so the HFCM can't make air, it has to be pulling it in, it has to be something to do with the filter/cap/o-ring or installation.

I did some quick reading and it sounds like there is a valve in the HFCM housing that gets opened when a filter is properly installed, otherwise you get no fuel from the tank. There is also a flapper valve that prevents backflow into the tank, also in the HFCM.

Haven't taken one apart myself, but the first one sounds the most suspect. I read where folks have cross-threaded the cap and it allows air in...

So, what does extremely close inspection show you? (also in the HFCM)

 

Well after another inspection of all parts I still did not see anything wrong. So I went ahead and replaced the fuel pump. While I had the lines off I figured that it would be worth a shot to hook up the air compressor and backblow the fuel lines back into the tank apparently there is no one way valve here as I heard the air bubling in the tank, with hopes of cleaning anything out of the way that may be blocking fuel from getting to the pump. After installation of the new pump I did a cycle with the key and the bowl open. Still lots of air. I cycled a second time and YES!!! The air bubbles stopped and we were pumping fuel again!! So I'm not sure if it was the backblow of the lines or the new pump but we are back to life. I want to thank you guys for all the help and ideas. Have a great day!

 

Glad you got it.