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Discussion Starter #1 (Edited)
Hello everyone... First time posting here.

This vehicle died on the road and hadn't shown a sign of loss of power, fuel leaks, etc..

What I've done and noticed:
1. Getting 2 codes, P2291 and P0627.
2. Noticed tank sucked in, possible cap not able to breath or release pressure. Released cap and heard air/vacuum being released.
3. Replaced both fuel filters.
4. Replaced pressure regulator on left side rear rail.
5. Noticed no rust nor metal on regulator valve on rear of left side rail.
6. Replaced HPFP from a used engine (metal particles evident on old pump, rollers were gone).
7. All fuses and relays are ok.
8. Unable to test for actual fuel pressure on the low side, but there's plenty going to the fuel system.
9. Disconnected fuel pressure sensor, still no start

I know all parts should be replaced, but we're trying to stay on the low side of costs.

Any help is greatly appreciated. I've read through other posts and still can't reach a fix. I'm going to tap into the output of the secondary filter and see actual pressure. I'm assuming it's suppose to be 50-75 psi correct?,

Thanks,
Ben
 

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Discussion Starter #2
Still need some help..

Checked low pump pressure and it's around 80 psi. Not sure why I'm getting a p0627 code if the pump is working.

Could it be a PCM issue which is why it's not running?

Forgot to mention but this vehicle was also hit from behind, but ran fine until the next day when it shut down on the road. The safety switch was checked and pump runs fine, but doesn't explain why the p0627 is active.

Any help would be greatly appreciated.

Ben
 

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Discussion Starter #4 (Edited)
Any luck figuring it out?
Heck no...no luck. Replaced a (HPFP twice , rails, LPFP, injectors, inj lines cross over new, all other used), FRP sensor, new pressure regulator. Parts came from a good engine. Updated PCM with inj codes.

I put a gauge on a T out of the secondary filter and getting 60psi while cranking. Checked on another 6.7 running engine and got the same 60psi.

I put a high pressure gauge on the high side and getting 135 psi. Don't know what's not allowing it to build up pressure.

Wondering if the 2 used HPFP are bad.

I even took the unloader valves off from HPFP and they weren't stuck. Pump internals look fine to me.

Dropped the tank and everything checked ok. Cleaned dirty breather.

What I don't like the sound... is sounds like air whizzing close to the HPFP. On both pumps put on.

Only getting P2291 code..

If anyone has experienced this and might have a clue, please let me know. In my 30 years of being a diesel tech, I've never had one this bad.

Ben
 

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Mr. Crossthread
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Remove the return line on the drivers side fuel rail, run the hose into a bucket and run the fuel pump. That is how I purge the low pressure side of a 6.7, the high pressure side just requires cranking on it until she fires but it shouldnt be very long. Im going to try and find a diagram of the 6.7 fuel system we can use to help diag.
 

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Mr. Crossthread
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Here we go.
 

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Discussion Starter #7
Remove the return line on the drivers side fuel rail, run the hose into a bucket and run the fuel pump. That is how I purge the low pressure side of a 6.7, the high pressure side just requires cranking on it until she fires but it shouldnt be very long. Im going to try and find a diagram of the 6.7 fuel system we can use to help diag.
I've disconnected that return lines several times, but not to bleed. I'll have to try that. buy geez you'd think it would self bleed after so many times cranking it.

What I did notice, and I could be wrong, but shouldn't there be any fuel coming out of the brass tube on the fuel rail? I believe the pressure regulator valve is a normally close valve. We replaced a new pressure regulator valve and still fuel is being relieved on the brass tube back to the return.

Ben
 

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Mr. Crossthread
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I've disconnected that return lines several times, but not to bleed. I'll have to try that. buy geez you'd think it would self bleed after so many times cranking it.



What I did notice, and I could be wrong, but shouldn't there be any fuel coming out of the brass tube on the fuel rail? I believe the pressure regulator valve is a normally close valve. We replaced a new pressure regulator valve and still fuel is being relieved on the brass tube back to the return.



Ben
This way you can see if theres a bunch of air in the lines. I've seen the PCV cause some really weird things with fuel pressure.

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Discussion Starter #9
Should there be any fuel coming out of that tube back to the return even with just the key on?

I don't think there should be any coming out, as you would think the high pressure pump would need all the pressure and not being relieved by the PCV during startup.

Via a snap on modis, getting 20% duty cycle for the VCV and PCV.
Ben
 

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Mr. Crossthread
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Should there be any fuel coming out of that tube back to the return even with just the key on?

I don't think there should be any coming out, as you would think the high pressure pump would need all the pressure and not being relieved by the PCV during startup.

Via a snap on modis, getting 20% duty cycle for the VCV and PCV.
Ben
Ohhh I didn't realize we were dealing with actual PIDs, most of the time we dont get that on here. Lol I tell you what, when I get to the shop in the AM I'll look at my PID list and I have all the normal readings for 6.7s printed off. I can also post Ford's diagnosis steps for your codes if you would like.

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Discussion Starter #11
Thanks for the help.. I have access to this truck on the weekends and every time I think I have it figured out, I'm back to square one.

I've bought so much literature to get up to speed on the 6.7 and downloaded a bunch as well.

Ben
 

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Mr. Crossthread
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Fords diag is pretty much just checking to make sure you have low pressure fuel and that it is clean diesel.


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Discussion Starter #13 (Edited)
Thanks.. I have that powertrain manual.

Just wish I knew why it doesn't build up pressure on the high side when I know for sure the low side is good.

Also that I'm curious if there should be any PCV relief on the driver's side fuel rail on start up.

Is 60psi enough for the lowside?

Ben
 

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Discussion Starter #14
Coming to a close with a bad PCM. No duty cycle at pin E22 which explains why the PCV is staying open and building up pressure.

Ben
 

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All that work and the result is a bad PCM. Glad you figured it out.
 
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