P2291 code
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4wd Low
Joined: Nov 2022
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P2291 code
he other day after my truck died on me it was getting a P2291 code. I originally thought my HPFP crapped out. I even had a guy come out and look at it and he thought the same thing even though he barely did any diagnosis on it. It ended up just being air in the fuel line. Before ordering a pump, I decided to cycle the key about 8 times to clear any air out if that might be the issue, and after that, it cranked right up and has not messed up since.
I want to share a very amateur shade tree mechanic theory on what happened and see if any of the more knowledgeable guys here think it could be what happened or not to get air in the system.
When it first shut down on me I popped the hood and noticed that the mass airflow sensor was unplugged. No telling how long that had been unplugged. And I believe that can really trough off the miles to empty readout on the dash. It shut off on my after filling up with diesel. It was showing about 40 miles to empty when I filled up. I typically do not let it run that low but I had just got back home from a weekend trip and there was not a station along the way to stop being backwoods country roads. After filling up I cranked it and went to pull off and it shut off and would not crank back up. My thinking is that the miles to empty was way off and I was really on fumes when I pulled in to fill it up and that caused some air to get into the line. But given my knowledge of all of it, I could be completely wrong also.
I want to share a very amateur shade tree mechanic theory on what happened and see if any of the more knowledgeable guys here think it could be what happened or not to get air in the system.
When it first shut down on me I popped the hood and noticed that the mass airflow sensor was unplugged. No telling how long that had been unplugged. And I believe that can really trough off the miles to empty readout on the dash. It shut off on my after filling up with diesel. It was showing about 40 miles to empty when I filled up. I typically do not let it run that low but I had just got back home from a weekend trip and there was not a station along the way to stop being backwoods country roads. After filling up I cranked it and went to pull off and it shut off and would not crank back up. My thinking is that the miles to empty was way off and I was really on fumes when I pulled in to fill it up and that caused some air to get into the line. But given my knowledge of all of it, I could be completely wrong also.
5th Wheeling
Joined: Feb 2024
Posts: 27
Likes: 7
From: Central Wisconsin
Your logic is sound. It's a closed loop system aside from the tank. If you did go that low and got some air from the tank, you could have gotten some other gifts from the tank as well. My gut would say replace the filters and purge the water separator just to be safe. That fuel system is expensive and difficult to replace/repair. Good luck
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4wd Low
Joined: Nov 2022
Posts: 12
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Your logic is sound. It's a closed loop system aside from the tank. If you did go that low and got some air from the tank, you could have gotten some other gifts from the tank as well. My gut would say replace the filters and purge the water separator just to be safe. That fuel system is expensive and difficult to replace/repair. Good luck
Thanks for the response and for confirming my theory. I am a very mechanically inclined person but diesel is fairly new to me. I come from an HVAC mechanical background. So I pick up on mechanical and electrical stuff pretty easily.
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4wd Low
Joined: Nov 2022
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Not really. Just a ten-foot trailer with a gas golf cart about 50 miles. Then about 5 miles to the gas station with no towing. This might make me sound and feel dumb but what is GFL?
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4wd Low
Joined: Nov 2022
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I changed both the fuel filters and the water separator valve on the HFCM and never could get the HFCM to push the diesel up to the top filter. I went to the parts store, picked up a new HFCM, and replaced it. Now it will pump the diesel just fine. It has about 5 psi at the fuel cooler. I bled both sides of the cooler until no bubbles. Then I crank it and it will run for about 3 – 5 seconds and shut off. Then it has bubbles again. I start the whole prosses over and get the same result. I spent most of yesterday doing this.
I think I might be sucking air from the input side of the HFCM from the tank. It sounds like air going into it. I am wondering if there is an issue with the O-ring in that fitting, and if so, is there a way to replace it? Or would it be better to just get some diesel-rated rubber fuel line and hose clamps to replace part of that line? Go back to a place I can cut open to install the hose over it and then on the input of the HFCM.
I think I might be sucking air from the input side of the HFCM from the tank. It sounds like air going into it. I am wondering if there is an issue with the O-ring in that fitting, and if so, is there a way to replace it? Or would it be better to just get some diesel-rated rubber fuel line and hose clamps to replace part of that line? Go back to a place I can cut open to install the hose over it and then on the input of the HFCM.
5th Wheeling
Joined: Feb 2024
Posts: 27
Likes: 7
From: Central Wisconsin
Do you have the service manuals? They would show the procedure if there was one. If you don't, PM me.
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4wd Low
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I have the manual and know the procedure for bleeding air. It just seems like it is sucking air at the pump to me, on the line coming from the tank into the lift pump. It was really hard to get the line on the new pump. I have some 1/2-inch diesel-rated hose I might try and replace that line with. I have not had time to get back on it since I last worked on it Sunday. Work has me all the overtime I can do right now. Probably will not get back on it until Thursday or Friday. Before I change the line, I might try and pull it off the pump and lube it up and reinstall it. Also, disconnect the connector holding the lines to the rail so it is easier to maneuver.
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5th Wheeling
Joined: Feb 2024
Posts: 27
Likes: 7
From: Central Wisconsin
Yeah, I didn't check if there was a procedure for that first. It was worth a shot. As far as the hose goes, it should work since it's on the suck side. I'm educated but ignorant about a lot of diesel things yet... that makes me an engineer (educated but ignorant ;-)
Good luck.
Good luck.
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4wd Low
Joined: Nov 2022
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Should the upper fuel filter housing hold fuel? After it fills up, it will drain back down. I am having a hard time getting air out of the system. I had a bad lift pump and replaced it. Every time I bleed the fuel and have no more air bubbles it will crank and then die after a few seconds.
I was bleeding the air again and after no bubbles, I unscrewed the top filter and all the fuel had drained back out of it. I do not think that is normal. Do I need to get a new upper fuel filter housing?
I was bleeding the air again and after no bubbles, I unscrewed the top filter and all the fuel had drained back out of it. I do not think that is normal. Do I need to get a new upper fuel filter housing?
5th Wheeling
Joined: Feb 2024
Posts: 27
Likes: 7
From: Central Wisconsin
That doesn't sound right to me either. Simple test. Try koeo and let it sit that way for a while. If the lift pump keeps cycling, you definitely have an issue. I have sat in that condition for 20+ minutes while coding with ForScan and the lift pump never cycled after the initial pressure building run.
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4wd Low
Joined: Nov 2022
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That doesn't sound right to me either. Simple test. Try koeo and let it sit that way for a while. If the lift pump keeps cycling, you definitely have an issue. I have sat in that condition for 20+ minutes while coding with ForScan and the lift pump never cycled after the initial pressure building run.
One thing I am going to make sure of when I get home today is that the lower filter is installed correctly. It was already installed in the housing when I purchased the HFCM. I did not think to check that when I installed the new HFCM. I did check to make sure a filter was in it.
On the bright side, I am learning a lot about a 6.4 fuel system, but I need to get it back on the road. I am supposed to be pulling my 5th wheel back home from the lake after the 4th weekend.
I have been researching what would cause the system to drain down like that but have not been that successful on finding answers of what all to check.
Thanks for all your help and responses.
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4wd Low
Joined: Nov 2022
Posts: 12
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The one on the rail is the one that came with the HFCM when I got it. It is a Motorcraft also. The one on the top filter is the one that came with the truck when I purchased it a couple of years ago. I have no reason to believe it is not the original. And filters are motorcraft. I will not by any oil or fuel filter other than Motorcraft after reading all the horror stories people have had with other brands in the 6.4.
5th Wheeling
Joined: Feb 2024
Posts: 27
Likes: 7
From: Central Wisconsin
Is that just turning the key to the on position and seeing if it holds the 3-5 psi when the pump cuts off? Is it supposed to come back on if it does not? If so how long does it typically take for the pump to restart? I am pretty sure the pressure drops when pump cuts off, but I have never noticed the pump coming back on.
One thing I am going to make sure of when I get home today is that the lower filter is installed correctly. It was already installed in the housing when I purchased the HFCM. I did not think to check that when I installed the new HFCM. I did check to make sure a filter was in it.
On the bright side, I am learning a lot about a 6.4 fuel system, but I need to get it back on the road. I am supposed to be pulling my 5th wheel back home from the lake after the 4th weekend.
I have been researching what would cause the system to drain down like that but have not been that successful on finding answers of what all to check.
Thanks for all your help and responses.
One thing I am going to make sure of when I get home today is that the lower filter is installed correctly. It was already installed in the housing when I purchased the HFCM. I did not think to check that when I installed the new HFCM. I did check to make sure a filter was in it.
On the bright side, I am learning a lot about a 6.4 fuel system, but I need to get it back on the road. I am supposed to be pulling my 5th wheel back home from the lake after the 4th weekend.
I have been researching what would cause the system to drain down like that but have not been that successful on finding answers of what all to check.
Thanks for all your help and responses.
Yes, after the initial lift pump run, the system should hold that pressure. I have had that pressure hold 10-20 minutes while coding with the key on and the engine off. If it keeps having to run, there is a problem.
Yes, the pump should continue to cycle if it needs to to hold that pressure. I could absolutely be wrong on this... maybe another member can weigh in with more knowledge.
I have never seen it restart. Usually, after the pump achieves pressure, I start the truck. When coding, it has not re-started... at least in my experience. My experience with coding usually ends with a key cycle off/on, but the pump has never run again after one. I just start the truck. I have been able to go into a store for 10+ minutes and when I came back out, the truck just starts without the lift pump running. I always wait for the lift pump to finish if it does run.