Air intrusion with electric fuel pump

[mr_smith]

92 7.3 N/A

Got this truck for a steal and it had bad air intrusion. I did caps rings olives New line in the engine bay. I swapped an old style fuel filter head out as well.

I also had a new mechanical pump laying around so I threw it on. That's where my problems began.
I know very well how to make sure the lever is under the lobe.

Long story short, I went through 3 mech fuel pumps, tested before they went on the truck, but every time as soon as I installed them, they failed. I would put a known good pump in, crank it some, take it out and the pump would be bad.

I got tired of trying to figure out why so I put a cheap electric fuel pump in it. 4-7 psi 36 gph. I hooked it to the bad mech fuel pump outlet (could this be an issue besides the arm possibly breaking off?)

The issue I am having is that I am getting air at the Schrader valve.. If I hold the valve open after cranking, I will get very bubbly frothy fuel and after a second I get a solid stream of diesel. Crank again.. Same issue

When I first put the electric fuel pump on, idled fine for 10 minutes and then died when I hit the accelerator.

Any ideas on why I'm getting so much air? Besides the potential for the arm breaking off, is there anything wrong with routing the fuel through the no working mechanical pump?

I would like to avoid spending too much on this truck as I don't know the condition of the trans yet..

 

[Mulochico]

If you route it thru the bad pump you risk getting fuel in the crankcase. If the diaphragm fails it will allow fuel to mix with the oil (very bad). Rule of thumb on here is either mechanical or electric, don't run them on the same line.

 

[Thewespaul]

Let’s see some pictures of your setup so we can better help you. What did you do for fuel filtration? Did you replace the soft rubber line that is near the frame that would feed the stock pump?

Try running the fuel pump off a bucket of diesel and eliminate see if that fixes your issues. If it does then you will know the issue is downstream the fuel pump, so fuel tank selector switch would be the next culprit

 

[icanfixall]

Testing thru the now failed mechanical lift pump wont hurt but... you best check the oil level before and after you try this. Many times the failure is the short rubber hose from the frame rail to the lift pump. Every movement of the engine will flex this hose. They don't last forever. Also please make sure the fuel tank level is kept above the 1/4 level. Usually the tank suction line breaks off and the last 1/4 tank of fuel can't be sucked out.

 

[hadley000]

Were the mechanical pumps made by Spectra? One failed in 600 miles on me, and another failed out of the box.

 

[Macrobb]

How did the pumps fail?

There isn't much to a mechanical fuel pump, really - just a lever, pivot, a diaphragm and a couple of flapper/check valves.

 

[mr_smith]

How did the pumps fail?

There isn't much to a mechanical fuel pump, really - just a lever, pivot, a diaphragm and a couple of flapper/check valves.

I have no idea. Even the old one I took out of the truck when it was running failed when reinstalled. The only clue I have is that the original pump had a lot of wear on the end of the arm. The can lobe showed no wear and looked to be in good shape.

 

[mr_smith]

Were the mechanical pumps made by Spectra? One failed in 600 miles on me, and another failed out of the box.

Yes

 

[mr_smith]

If you route it thru the bad pump you risk getting fuel in the crankcase. If the diaphragm fails it will allow fuel to mix with the oil (very bad). Rule of thumb on here is either mechanical or electric, don't run them on the same line.

I agree, decided to just block it off

 

[mr_smith]

So I unplugged the fuel supply line at the filter head and ran the pump.. Good clean stream of airless diesel. I even clamped down on the hose to simulate back pressure (probably unnecessary), no change.

So I have a good supply of diesel at the filter head inlet.

Crank, no start. Pump on, If I hit the Schrader valve I get about 1 second of air followed by about two seconds of frothy diesel followed by a good stream.

I'm going to attach a pic, I know it's ugly.. The name of the game right now is get her running again then I will pretty everything up

You must be registered for see images attach

 

[Thewespaul]

With the key on try unplugging the front plug on top of the ip you should hear a click as plug it back in. Have you tried cracking the injection lines and seeing if you have fuel there? Any smoke you get out of the exhaust shows you have fuel getting to the cylinders.

 

[mr_smith]

With the key on try unplugging the front plug on top of the ip you should hear a click as plug it back in. Have you tried cracking the injection lines and seeing if you have fuel there? Any smoke you get out of the exhaust shows you have fuel getting to the cylinders.

I'll go check that out.

Any idea how I'm getting all this air after the filter head?

 

[Thewespaul]

These filter heads are prone to that issue. Have you checked the condition of your fuel olives?

 

[mr_smith]

These filter heads are prone to that issue. Have you checked the condition of your fuel olives?

Olives are brand new. I have the old/original filter head. Maybe I should swap it back and see if anything changes

 

[Thewespaul]

If you didn’t have issues with the original head I would put that back on