6.7 extremely long crank

[Joshf250]

Just replaced the entire fuel system on a 2015 F550 because of a CP4 failure. Bled the system out and got the truck started but you can shut the truck off, crank it right back up and it will take 20-30 seconds of cranking for it to slowly start back up. Rail pressure starts around 3,500 psi and slowly works it’s way up. I pulled the fuel return line off of the left hand rail and a good amount of fuel is being pumped out of the rail while cranking. Swapped the fuel regulator and no change at all. Has anyone else ran into anything like this? Or am I just over looking something simple? I’ve done plenty of these replacements and never ran into any sort of trouble


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[6.0 Tech]

How much have you driven it? Sometimes they need to bleed all the air out which takes some driving


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[Joshf250]

I haven’t drove it all, I will drive it today and see what happens. I was trying to be cautious and not let something happen to this new system. I will give an update


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[co04cobra]

It’s probably just air. Need to drive it

 

[Joshf250]

I ran the truck for about 30 minutes, absolutely no change. What’s the chances of the CP4 being weak out of the box? This kit came from ford so it’s not reman stuff.


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[Joshf250]

Here is a video I took while the truck is running. When you rev it up at any RPM and let off the gas, the engine acts like it almost wants to die out, you can see the rail pressure drop down to around 4K psi


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[Sterling6.7]

Ok, I will ask the dumb questions. Did you change the fuel filter? Are you sure that it is seated all the way and not sucking air?

 

[webb06]

I still think you need to drive it 10+ miles. I don’t think just idling it is enough to get the air purged. Could be wrong.


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[Joshf250]

Ok, I will ask the dumb questions. Did you change the fuel filter? Are you sure that it is seated all the way and not sucking air?

The low pressure fuel system was replaced as well just to eliminate any variables there.


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[sootie]

is the HFCM filter housing tightened all the way to the plastic stop?

 

[Joshf250]

is the HFCM filter housing tightened all the way to the plastic stop?

Yes and I put a clear hose on the upper filter outlet to look for any type of aeration and there was none visible


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[Joshf250]

Ended up being the injectors returning to much fuel, picked up a new set of injectors and it’s cranking up perfectly now. Thanks guys


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[Tiha]

Did you test the return flow? or someone else?

If you did it, how? Would like some insight.

Thanks,

 

[Joshf250]

Did you test the return flow? or someone else?

If you did it, how? Would like some insight.

Thanks,

I did, a simple way to do it is bypass the return line going into the upper filter, pull the return lines off of one bank at a time and put small clear hoses on the return fittings on the injectors. Run those into a container where you can watch them. Command your low pressure fuel pump on and watch for fuel to come out of the lines. Whichever line has fuel coming out is your issue.


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[Joshf250]

GM has a injector return spec for the LML’s which use basically the same system as these trucks. I will see if I can go back and find that.


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[Joshf250]

The maximum return flow for one injector is 3 ml in 15 seconds at idle


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[webb06]

Was this a ford contamination kit you installed or aftermarket? Just curious


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[Joshf250]

Was this a ford contamination kit you installed or aftermarket? Just curious


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It was a kit directly from ford, they replaced the injectors no questions asked.


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[Tiha]

I did, a simple way to do it is bypass the return line going into the upper filter, pull the return lines off of one bank at a time and put small clear hoses on the return fittings on the injectors. Run those into a container where you can watch them. Command your low pressure fuel pump on and watch for fuel to come out of the lines. Whichever line has fuel coming out is your issue.

I have what I consider a long crank and I came to the same conclusion that I need to do a return flow test. But everyone told me I was crazy and you can't do it on the 6.7. That ford has no spec for return flow.

Was thinking about just like you are talking, but haven't gotten to it yet.

 

[co04cobra]

It was a kit directly from ford, they replaced the injectors no questions asked.


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Did that fix the problem?