For it to lose suction, its got to be an air leak. Be ready to pump the excess fuel out of the tank and into something clean... buckets maybe. Harpoon mod, just cut the vent, thats all you really need to do for that one to work. make sure the foot valve is on the pick-up tube.

Your suction issue is above the fuel line if that helps. So that should eliminate anything above whatever the level is in the tank. The pump is loosing it's prime, why your having to re-prime the pump several times with the key.... to remove the air. So, thinking this way... look for a discharge leak (drip) from the pump to the secondary fuel bowl and if you find no leak.... look for an air (suction) leak from the tank connection to the pump.

Hope this makes sense? I believe you issue is between the pump and the tank.

 

Yes it makes sense, i agree that the leak is between the pump and tank. I'm not seeing any leaks on pressure side of the pump. I havent looked at all of the connections from the pump to fuel bowl, but haven't seen any drips under the truck either.

I'm thinking whatever seal on the part that is leaking gets smaller in the colder temps and causes it to lose the seal and leak. Once it's warmer out the seal or oring or whatever expands and the pump can get fuel. It has probably been bad for a while, but with warmer temps didn't show. Now that is cooled off a bit is become a problem. I know the quick connect fittings have orings inside and i suspect either one of those or a similar type connection. The other fittings and the fuel pickup i am unfamiliar with.

 

You have a quick connect both at the tank and at the pump inlet. I moved my HFCM to behind the transfer case so it was more accessible, and when I did I replaced the lines between the tank and pump with diesel rated fuel hose. If you do have a quick connect issue, you can either get a complete line assembly from Ford, although there are aftermarket fixes available. I'd do the diesel rated hose.

The other thing I would do is get a replacement pickup foot. There have been instances where the foot's suction blow off valve has gone bad, and when that happens you start to pull air at 1/4 level in the tank. If you got it apart, IMO it's worth the cost to put a new pickup foot in place. If your really down on dollars, the other option is to plug the valve hole with a freeze plug, if your not in a freezing environment.

I've pulled the tanks on several vehicles and it's not that hard, but tie down straps front and rear of a nearly empty tank makes life a lot easier.

 

Exactly what I'd like to do - get rid of the quick disconnects just to eliminate the possibility of having a problem there. Regarding the diesel rated fuel line, do you happen to know the size? Also, how did you make the connections to the tank and hfcm and mount the hose to the frame rail?

I will also go ahead and order the new fuel pickup.

After driving yesterday the tank is nearly empty.

Thanks for the info, seems i am on the right track but i guess I'll know for sure this weekend

 

Ready to drop the tank today but i didn't have the right quick disconnect tool. Trip to autozone, decided might as well rent some tools and diagnose this problem the right way rather than stabbing in the dark. Picked up a fuel pressure kit, disconnect kit, and vacuum tool.

Hooked up the fuel pressure gauge to the hfcm outlet (to engine) and had my son cycle the key. To my surprise the gauge pegged out at 100psi. From what I've learned over the past week the fuel pump has a built in pressure regulator of 100psi.

So what does this mean? I guess no suction problem. My next guess is the fuel bowl standpipe. Somewhere along the line i read it can cut fuel supply to the bowl if it's not working properly. It could be a restriction in the fuel line too, but hard to believe it would be plugged up.

I just rebuilt the pressure regulator (blue spring) and I'm pretty sure that is ok.

Any ideas?

 

What are you using to read pressure in the truck? May want to confirm its not your gauges going wonky.

 

Three questions.
1. Are you using Motorcraft filters?
2. Is your filter twisted or crushed in anyway?
3. Is you stand pipe tight or does it wiggle any at all.

A twisted filter has driven a lot of us up the wall (me) trying to figure out usually low fuel pressure. A very cheap try is to replace upper fuel filter carefully. Motorcraft, not one with same specs.

 

I have been using my isspro ev2 to read pressure. I have not hooked another gauge up to verify it is working properly. It zeros out like it is supposed to. I had a sender go bad a few years ago when it was mounted directly to the test port, but isspro sent me a new one and is mounted by the degas bottle. May as well check it just to be safe.

Racor filters are what i have been using since I've owned the truck in 2010. I've never had a problem with them. Don't they supply to ford?

The other day i switched my oil filter cap with the fuel filter cap to see if that made a difference, it did not. I also checked the fuel bowl filter and it didn't feel right when i tightened it up. Today when i opened it up i found a piece of plastic in the bottom. It was from the stand pipe. This was after my earlier post. Once i had the stand pipe out, i found 2 more broken tabs inside. Not sure how i managed to do this the other night. The filter was also twisted/crushed a little. After replacing the standpipe, pressure came up to 45 right away, and after a few cycles to 55. It is still not acting what i would call normal.

Took a drive and put 10 gallons in. Pressure drops 5psi if i accelerate hard for a long time but comes right back up. It never went below 60 while driving. I still don't think the problem, whatever it is, is fixed. In the morning when it is cold i will see what happens when i cycle the key. I will also test my fuel pressure gauge, but i am pretty sure it's ok.

Maybe changing to a motorcraft filter will help. Ive spent a lot of time messing with this and if that's what this comes down to i will be surprised.

Changing the fuel pump I'm not sure it was needed. This one sounds quieter though for whatever that's worth. My fuel pressure would sometimes get stuck at 50 or 55 while driving on the freeway. It has always bounced around 2-3 psi. I think doing the regulator helped with that because it is solid 65 now, no bouncing.

 

I spent 3 days chasing this on mine. I couldn't believe it either. You said there were 3 pcs of plastic pcs. Did the other two come from the cap?

 

Its not unusual to see a +/- 5 psi drop on a WOT run.... as long at the pressure doesn't go below 45 psi, the injectors are safe. I'd be concerned if you were at 65 psi and saw a drop to 50psi on a full throttle run... sounds like you may have corrected most of the issues. It's not unheard of to have a bad blue spring either (regulator spring).

Racor supplies Motorcraft filters... same, same.

 

The other 2 pieces of plastic were still suck in the standpipe. They were part of the standpipe, the little tabs on the collar that slide up and down. I will get a picture up tomorrow.

I got the fuel pressure test kit hooked to the fuel pressure test port. Luckily one of the adapters in the kit fit right where the extension hose came off. Got a solid 60psi, but we'll see what it looks like in the morning.

Thanks for confirming the fuel filters, thought i was losing it there for a minute

 

Exactly... verify everything!

 

I've been following and agreeing with suggestions here so nothing to add, until you wrote this:

One of the worst purchases I've ever made. Confirm the gauge.

While you had standpipe issues that you caught, early on I should have brought that up, even without knowing what you were using. Instrumentation checks was always the first thing we did with any wonky data.

 

Well to no ones surprise it seems, the sending unit is bad. Cycled the key this morning with the test kit hooked up and got 60psi almost instantly. Hooked up my sender and it did the same thing its been doing. Hit it with my wife's hair dryer to see how the heat would affect it, pressure came up to 60psi.

I called isspro but they are closed on weekends. Hopefully they'll send a new sending unit, 2nd failure in 5 years. Last time the unit would not zero out so I'd get a zero reading of like 20 and readings of 80 - 90. Pretty obvious it wasn't working right.

Lesson learned here, wasted time and money. At least my truck is ok. Thanks all for your time and input.

 

Go fishing Bill.... glad you got it.