Air intrusion problem

[Jared321]

I have a 1988 7.3 idi, I having air intrude into the lines, i checked for leaks and fixed all I could find then was told to replace injection pump so I did. I have an small electric fuel pump on my frame rail I unhooked the side where it pushes fuel and it’s was just spitting fuel and wasn’t constant fuel pressure. Could this be because the pump is clogged or could it be something from fuel not being picked up from the tank or air intruding threw the fuel tank selector.

 

[Joseph Davis]

Got a Vacuum pump, see if you can pull fuel through the pump and out of the tank; if you can, replace pump. Good Luck

 

[DrCharles]

Could this be because the pump is clogged or could it be something from fuel not being picked up from the tank or air intruding threw the fuel tank selector.

Yes.
(Could be any of those things).

Those small cheap pumps never seem to last for long. Get a Facet Duralift (40285 seems to be the most popular). They are relatively expensive (around $100) but they're made for diesel, rated to pull as well as push, and have a built-in clear bowl/filter.

 

[icanfixall]

Welcome to the forum. These trucks usually have broken fuel tank suction lines so the last 1/4 tank can't be sucked out. To first make sure you have bout a 1/2 tank of fuel.
As already posted the small electric pumps wont work well if at all. . Sometimes finding where the air is getting in can be ruff but its doable. Look at the filter head. See the exit line to the injection pump..That has a rubber sleeve in both ends. you MIGHT be able to tighten those brass nuts enough to stop an air leak but replacing them is the best idea. They harden over time and leak air in but not fuel out. air has a smaller hole to leak from than diesel.Also the line from the lift pump to the inlet of the filter head has another sleeve in it too.Try tightening that nut but again.. Replacing it is a better idea. Finally the rubber hose fuel line from the frame to the mechanical lift pump can rot and leak air. Especially because its on the suction side of the mechanical lift pump so air sucks in easier than fuel can be pushed. hope this helps you find the air leak.

 

[Jared321]

Thanks for all the help, I’m new to the forum. But I realize today my return lines are plugged up, they don’t go to the tank or the filter. Could his be my problem?

 

[Jared321]

Also if this changes anything, the truck is really hard to start but once I get it started it runs like nothings wrong

 

[icanfixall]

How can you tell the return lines are plugged up??? No matter the return system.. They ALL MUST return to a fuel tank your drawing fuel from. Please expand on your comment or post some pics so this forum can better help you...

 

[Jared321]

Sorry I didn’t take a good look at it, it’s not hooked up to the top of the fuel filter, but Is hooked to tank. But basically what’s happening is the truck only starts when block heater is plugged up for awhile and it will start back up within 2 hours or so about restarting. There was air in the fuel but I pretty sure I got it fixed after sealing some leaks (now there is no air coming out of Schrader valve) but still won’t start unless block heater plugged in. The glo plug relay was replaced, I checked the glo plugs and there was 1.2 ohms running threw all of them. Is 1.2 ohms bad?

 

[Joseph Davis]

Is the gas cap vented meaning allow air in but not out? moving fuel out of tank and not return fuel to tank will vapor lock the system. check after you drive 10 miles and stop and crack gas cap and listen for air rushing in. That will mean negative pressure building in tank and stopping fuel from entering fuel filter causing no start. I know because I bought new gas cap for truck but it sealed tighter than a drum and with an electric fuel pump I could see no fuel entering fuel pump because of glass filter I installed. I opened gas cap and air rushed, I could see fuel in filter, bought a new gas cap it is vented to out side air. Now No problems with long starts. Good luck figuring it out.

 

[IDIBRONCO]

I don't remember the ohms specs for the 7.3 glow plugs, but at least you know that they're not burned out. If they were, you're reading wouldn't change. Is your glow plug controller getting power to it? Is there power going to your glow plugs from the controller. I realize that you just replaced it, but it could be bad even though it's new.

 

[IDIBRONCO]

Is the gas cap vented meaning allow air in but not out? moving fuel out of tank and not return fuel to tank will vapor lock the system. check after you drive 10 miles and stop and crack gas cap and listen for air rushing in. That will mean negative pressure building in tank and stopping fuel from entering fuel filter causing no start. I know because I bought new gas cap for truck but it sealed tighter than a drum and with an electric fuel pump I could see no fuel entering fuel pump because of glass filter I installed. I opened gas cap and air rushed, I could see fuel in filter, bought a new gas cap it is vented to out side air. Now No problems with long starts. Good luck figuring it out.

It does sound like he's got the air intrusion problem figured out now. I think he needs help with the glow plug system.

 

[Joseph Davis]

Sorry take a strand of wire ground it and take other end and touch it to white wire on glow plug relay with key on if it clunks it is working, if it rattles like a snake; replace it. I think glow plugs are 0.5 to 0.9 at K setting. not 1.2 that would be on the higher side but it would light a test light bulb. Hook up test light to positive side battery and touch each top of glow plug if it lights good to go. Hope it helps Good Luck

 

[Jared321]

Thanks guys, I have one glow plug that doesn’t light up at all. Also my relay will tick after 10 seconds. I heard that if one is bad it messes with the relay and won’t let them cycle properly. Is this true?

 

[DrCharles]

One bad plug short-cycles the controller some, two or more makes the system basically useless. Bottom line is, you need 8 good Motorcraft GP's.

 

[hadley000]

While you're changing the GPs I'd also plan on replacing the ends on the wires that go on the plugs. If they haven't been changed yet they're probably crumbling away and corroded. You're already in there and it won't cost much more to make sure they have good connections. When I did mine I used heat shrink bullet connectors.