6.7 extremely long crank

Joshf250 · Oct 21, 2022

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 · Oct 21, 2022

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

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Joshf250 · Oct 22, 2022

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 · Oct 22, 2022

It’s probably just air. Need to drive it

Joshf250 · Oct 23, 2022

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 · Oct 23, 2022

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 · Oct 23, 2022

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 · Oct 23, 2022

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 · Oct 24, 2022

Sterling6.7 said:
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 · Oct 24, 2022

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

Joshf250 · Oct 24, 2022

sootie said:
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 · Oct 26, 2022

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 · Oct 26, 2022

Did you test the return flow? or someone else?

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

Thanks,

Joshf250 · Oct 26, 2022

Tiha said:
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 · Oct 26, 2022

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 · Oct 26, 2022

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

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webb06 · Oct 26, 2022

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

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Joshf250 · Oct 27, 2022

webb06 said:
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 · Oct 27, 2022

Joshf250 said:
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.