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bubbles in fuel bowl

14298 Views 38 Replies 7 Participants Last post by  upnorth the Bilge Rat
I get air bubbles in the upper filter bowl when I cycle the key.
I've cycled it and emptied the bowl several times and continue to get bubbles.
It also seems to fill really slow and stops filling after about 20 seconds.
It takes 2 to 3 times of cycling it to fill the bowl to the top.

The truck was running poorly, no power, no boost. I changed both filters did the priming sequence thing it started, ran for a minute and now won't start.
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I ran a clear line from the tank pickup unit to the hfcm and a clear line from the engine side of the hfcm to a container all other lines are on their normal connections.
Ahh, then cap both return ports on the HFCM, likely pulling air from the return, either thru the tank or the filter housing

The low flow is concerning, just had mine off a while back to check how low it would go before I was out of fuel (138 miles ...lol)
anyways the fuel flowed out of the line about 2-3 inches with the line horizontal
this all depends on if you have a restriction in the tank or in your line adapter
you could place the end of the clear line an a clean container to see if the pump flow increases

The pickup foot is gone in my tank, that is why it runs out of fuel at 138 mile -- the after market foot is not of quality so I am told
so looking into a sump kit, or possibly making a sump -- I have the tools
just can't see boring a 3 inch hole in my tank, ...lol
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Ahh, then cap both return ports on the HFCM, likely pulling air from the return, either thru the tank or the filter housing

The low flow is concerning, just had mine off a while back to check how low it would go before I was out of fuel (138 miles ...lol)
anyways the fuel flowed out of the line about 2-3 inches with the line horizontal
this all depends on if you have a restriction in the tank or in your line adapter
you could place the end of the clear line an a clean container to see if the pump flow increases

The pickup foot is gone in my tank, that is why it runs out of fuel at 138 mile -- the after market foot is not of quality so I am told
so looking into a sump kit, or possibly making a sump -- I have the tools
just can't see boring a 3 inch hole in my tank, ...lol
I had pulled the pickup unit out earlier, it looked new.
Looks like I have a few more things to chase down.
I may measure the amount of fuel that comes out. It doesn't push with much force, more like falls out of the end of the hose.
I checked the amount of fuel it pumps when cycling the key on. I cycled it twice it pumped out just under 8 ounces of fuel.
I also rechecked to make sure I had the right torque on the cap.
I'm not sure if I need to mess with the air bubbles too much more at this point. If it looks like I need a new pump, I'll end up going through the hfcm anyway.
Ideas?
I checked the amount of fuel it pumps when cycling the key on. I cycled it twice it pumped out just under 8 ounces of fuel.
I also rechecked to make sure I had the right torque on the cap.
I'm not sure if I need to mess with the air bubbles too much more at this point. If it looks like I need a new pump, I'll end up going through the hfcm anyway.
Ideas?
There is not a torque on the filter cap -- it is until it stops turning, there is a stop on the threads unless it has been broken
it is a definite stop
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Here’s my favorite fuel trouble shooting video. I think it says also that the low pressure can be caused Be a clogged line from the tank to the pump and this explains how to check that.


When I first read the title, I thought this was a fuel injector related thing from the upper fuel bowl failing a bubble test.
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Here’s my favorite fuel trouble shooting video. I think it says also that the low pressure can be caused Be a clogged line from the tank to the pump and this explains how to check that.


When I first read the title, I thought this was a fuel injector related thing from the upper fuel bowl failing a bubble test.
I had the same flow out of the hfcm after bypassing the factory lines from the tank pickup to the hfcm.
I doubt that line is plugged or restricted.
I'll probably do some fuel pressure checking after I get past the hfcm problem.
Thanks!
Well poop!
I went to a junk yard picked up a used hfcm. Spent awhile cleaning it. I mounted it back on the truck ran my clear hose from the tank to the hfcm and a clear hose on the engine side of the hfcm to a fuel can. I had both the smaller lines from the hfcm plugged off. After cycling the pump on a few times I got clear fuel (no air bubbles) coming out of the hfcm.

The used hfcm pumped a lot more fuel then my original one, so I'd guess the original had a bad fuel pump.

I removed the clear line from the tank to the hfcm and attached the factory line and plugged in the two smaller lines with the factory connections I left the clear line from the hfcm on the engine side draining into a fuel can.
When I cycled the key on I pretty much got fuel that looked like foam coming out of the hfcm.
I replaced the factory line from the tank to the hfcm with black rubber fuel line, still had the same foam coming out.
I plugged off the two return lines one at a time and tested. The air seems to be coming from the engine side return line.

I guess the hfcm has a check valve that isn't working right?

Would it be a dumb idea to reconnect everything and see if it clears up with all the plumbing connected?

I was trying to avoid buying a new hfcm if all I now have is a fuel line sucking air.
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What’d you do to fix it?
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The pump can suck air down the return line from the upper filter
under "working" circumstances that line is filled with fuel,
since the pump delivers more fuel than the engine can use

Did you look at @TooManyToys HFCM video? shows how the inner workings of the pump
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The fuel supply is critical to good operation and to the health of EXPENSIVE injectors.

Glad it is running now, but buying a used HFCM from a junk yard is just asking for problems IMO. Who knows how long the seals in it will last - or even the pump.

In addition, low fuel pressure will kill injectors. Failed injectors could damage the engine.

I have serious doubts that your current approach to fixing the 6.0L will give you long-term success.
What’d you do to fix it?
I pretty much covered it in post #30.
I didn't want to spend a ton of money and find out my pump was good. I had a good idea it was bad.
I picked up a used hfcm for $80 from a junk yard, I wasn't taking too much risk with the used one, they would take it back if it didn't work. I cleaned it to death and put it back together. It works just fine although I'd still like to run a pressure check up top and do the blue spring kit.
I did bypass the stock line from the tank to the hfcm, I didn't like the way it's connection to the hfcm felt, it seemed sloppy.
On the plus side the used hfcm I picked up had a brass water drain plug.

I should clean up the old one and see if it just isn't plugged up internally.
You still don't know what risk you have incurred until you check fuel pressure............. And even then, the failure rate of a junkyard pump has to be higher than that of a new pump - making a fuel pressure gauge even more important. The 6.0L will run fine on fuel pressure that is pretty low - right up until an injector fails.
You still don't know what risk you have incurred until you check fuel pressure............. And even then, the failure rate of a junkyard pump has to be higher than that of a new pump - making a fuel pressure gauge even more important. The 6.0L will run fine on fuel pressure that is pretty low - right up until an injector fails.
You are right.
I will be checking it. I just have to get the stuff together to do it.
I'm running out of summer quickly.
Yknow, the fuel pump by itself isn't that expensive, nor is the service kit for the hfcm. Why not just "rebuild" the one you took off?
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Yknow, the fuel pump by itself isn't that expensive, nor is the service kit for the hfcm. Why not just "rebuild" the one you took off?
It was a time and weather issue.
In a couple weeks we'll start getting frost at night and I was working between heavy rain storms. The truck sat for for days with the bed on the ground next to it because of the constant heavy rain. working on the top side in a little rain isn't a big deal but laying under the thing in the rain is out.
I will probably rebuild the original hfcm and keep it on hand. If I see a pressure issue with the used one I'll be go to go.
Mail delivery as be a bit messed up lately, some stuff arrives at normal times some stuff takes forever. I didn't want to order something and have to put it on in the snow. I'm not a total wimp I've changed a starter more then once in below zero temps.

I didn't know there is a service kit for the hfcm. I'll look into that.
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