Maintenance day, oil change and fuel filters change

Oil change, no sweat.

Fuel filters, lots of sweat...
Sweat, because after a full round of priming the engine fired and ran for two seconds and stopped.
I tried priming again, same way I've always done, just as I had to begin with, 6 full key on cycles for 20 seconds, off for 5 seconds and repeat.
NOTHING, just cranked and cranked.
Turned the key on, got down by the fuel tank and could hear the lift pump running as it should.
Cracked the drain on the separator, fuel ran out.
I thought maybe the fact that the truck was sitting up on ramps may have made it so the lift pump wasn't getting a full pull on the fuel as it was down to just under a 1/4 tank so I rolled the truck off the ramps but it didn't help.
Talked to a guy I know who runs a diesel shop, he says I should not be replacing both filters at the same time, says I should be replacing the separator first, running the engine, then stopping it and doing the engine mounted filter, which I've never done before and never had a previous issue
Suggested pulling the supply line to the engine filter to make sure the fuel is getting to it, if so, then put it back on and pull the outlet line from the filter to the CP4 and make sure the fuel is flowing through, says he sure it is full of air.
So, I did, pulled supply line, turned key on and it blew fuel out, hooked it back up to the filter and pulled the outlet line, stuck a pop bottle over the filter outlet to catch the fuel and turned the key on, and it blew nothing but foam into the bottle, so it was full of air. Had to keep cycling the key to keep the pump going and kept blowing foam until it finally started flowing liquid fuel. I hooked the line back up and tried to start it after priming it again and it still would not start.
Called my guy back again and he said I was going to have to keep turning the engine over to get the CP4 to start pumping fuel again.
So, I went back out and primed the system again, except I did 10 cycles instead of 6 and let the engine crank until it finally caught and started.
Shaky at first, then smoothed out, and I let it run for quite a while, then drove it around a while.

So, I am still thinking maybe the lift pump in the tank wasn't getting a good pull on the fuel while sitting on and angle with the tank being a little low.
I guess next change I will make sure it has more fuel in it just in case, but I've changed the filters before with just a 1/4 tank.

 

I wonder if your new engine mounted filter had a restriction in it? I was going to suggest reinstalling the old filter to see if it would prime properly but you appear to have solved the issue. Is it a Motorcraft filter? I realize with how often you change your fuel filters that you are aware of knockoff/counterfeit Motorcraft filters. Glad to hear you have it resolved.

 

Wow, well that's scary. Especially considering your previous fuel pump issue.

This brings a couple of observations and questions to mind.

I've read numerous places on this forum where people suggest changing the fuel separator with 1/4 tank or less to minimize the fuel drained from the separator. And I've never heard about changing one filter at a time, with a drive in between, but I'm relatively new at this diesel stuff compared to some of you folks.

If you are concerned about the lift pump not getting a full pull because the truck was on ramps, are you concerned the lift pump is not working at 100% at other times?

When the engine filter is changed, by default it is full of air. Where is the air normally supposed to go? Don't the priming cycles push the air through all of the fuel lines and the engine filter until it gets to the CP4? Then wouldn't the CP4 have to let the air go somewhere? Is that through the fuel injectors?

Isn't cranking the engine without fuel flow to the CP4 the kiss of death?

I'm always learning stuff here. I hope you aren't presenting an expensive lesson.

 

Oh, definitely a Motorcraft filter set, it is the newest part number with the new extra reinforced engine mounted filter.
But, it wasn't a filter issue, it was the air in the system, noted by the foamy fuel output, once that passed and it got a good prime in the CP4 it finally fired.

 

Some valid points you raise.
It was the earlier year models that I have seen talk about having low fuel levels to keep the draining of the water separator from drawing too much fuel from the system. I have never had this issue on my 2022.
And, up until today I was not concerned with the in-tank lift pump possibly not pulling the fuel as it should during low fuel level situations, although I generally try to not let the fuel level get that low, and never work my truck hard at less than a 1/4 tank.
And, yes, the filters are full of air when first installed, and they have to be primed to fill them with fuel and get the air out of the system.
As to where the air in the system would go, it should be following the route of normal fuel flow, and return to the tank through the return line.
And, I do not think that just running the CP4 without full fuel flow is the "kiss of death" unless the pump is already in trouble.
There really is no way around it anyway, it is part of normal operation, especially after fuel filter changes.
And, I have been running fuel lubricity additive religiously since my CP4 failure to do what I can to keep it going, so hopefully any issues with times of low fuel flow won't be any issue for the pump.
The pump is never "dry", diesel fuel doesn't dry up very quickly, so even if there is little or no new fuel flowing through it for a short time, there is still fuel present in it.

 

well good that you got it going....but your repair guy is not correct in that to continue to try to dry stsrt it so that the cp4 will pull fuel.....it will pull fuel..but with out proper fuel pressure the PCM wont let it start..so it will spin away on dry roller bearings.

my advice to is to check the cover on the tank mounted fuel filter access to make sure it is tight...because the in tank pump will pull air thru the cover if the cover is not sealed.

how tight...thats anyone's guess...I had the exact problem you did once and had hand tightened the 5 bolts with one of those handle nut drivers and if felt tight....but after the difficult start and being certain I had primed it enough I use a torque wrench set to 5 inch pounds and the bolts spun a few turns before the the torque wrench clicked. so that means my gasket oring did not have good compression. it started no problem after that with a few key cycles.

dont know what the "factory" torque should be and quite honestly if the air sucking problem continued I would have no issues with clicking up the torque to 6,7,8,9,10 etc until I was sure the gasket had adequate compression.

the whole housing is plastic and I dont know if there is a metal insert that the bolts go into so I can imagine that the plastic threads can be stripped...but for me that would not be the end of the world since I have a box of assorted brass inserts made to repair plastic thread holes.

 

I have no idea what tank mounted fuel filter access cover you are talking about???
And, as I said above, there is no dry anything inside the CP4, it may not be flush with fuel during priming or before, but is certainly not "dry".

 

tank mounted filter housing

the cover to access the fuel filter....5 bolts . there is a cover and an oring. the filter sits in the cover when you slide the cover down....move the filter and replace on the cover...then put the assembly back in with a new oring.

 

You mean the water separator filter housing???
That is a non-issue, if that was any kind of loose fuel would be leaking out during priming, it is under pressure when the key is on, it won't suck air in.
And, I don't consider that as "tank mounted", it is next to the fuel tank, not mounted on or in it.

 

the fuel is pulled thru the filter on the way to the pump in the tank.....its not under pressure....its under suction...flow is from draw tube…to filter..to pump

 

When I've changed fuel filters I have always done them both same time as well The only thing I do differently is I cycle the key on until the pump stops and off. Then back on again and continue until I don't hear any gurgling noises. I have never counted the cycles so I have no idea how many it takes but it is quite a few. To date mine has always fired right up without issue.
I have read about not changing them same time as well. Haven't given much thought to it beyond that to be honest.
The CP4 is always in the back of my mind though.