I know this has been covered before, but could someone please help me?
2004 3500 4x4 dually. 155xxx miles. Auxillary fuel filter. Fass pump. Bully dog plug and play set on tow. K&n cold air kit.
Wouldn't start last year during a week of teens temp...chalked it up to gelled fuel, even though I use diesel power service year round.
Started when plugged in.
This year, won't hardly start below 40 when not plugged in.
Changed grid heater and 2 solenoids.
Took to two different shops. Valves ran. Spill test within spec. Tube nuts tightened. Cp3 put on test stand-tested OK. Fass pump OK for flow an pressure. Changed fuel filters. Sent injectors off and tested OK. No burnt pistons. No codes thrown. One thing I saw looking over tech shoulder was a reading on lap top that showed a little less than 1000 psi. Once started, it went up to 6000 psi. I assume this is rail pressure. He chalked it up to bad injectors, but they tested OK.
What next? Nobody seems to know. Is it a rail relief issue?
Thanks for the help!

 

1000 psi rail pressure is too low for a truck to start. there is way to test your fca by unplugging it and cranking the over, but i dont remember exactly how you do that.

 

So is the FCA the culprit, or does that trick something else to raise the pressure?

 

it could be the fca. it controls the rail pressure. if it doesnt change when you unplug the fca then it could be a bad cp3, PRV or injector. but you already had your injector tested so you can cross that off.

 

Shop had the cp3 off and tested good on stand. Injectors tested and passed. Is the prv part of the rail? Thanks for the input, chief.

 

Can injector(s) be bad even if they pass testing?

 

Having to require the truck to be plugged in during low temps in order to start the truck, is a very common symptom of aging injectors. I would question if the shop that 'passed' your injectors was actually up to the task of testing them. Second to the injectors, I would check your battery's condition and voltage drop during cranking.
Good luck with the fix, back to morning brew . . .

 

yes it is

 

Half way through this video it shows the procedure for measuring return flow from the cp3 and from the injectors.


I think that is what I'd have done next.

 

How are your batteries and does engine crank over fast enough? Min cranking RPM is 125 if any lower you will have starting issues. Fuel pressure at the rail while cranking has to be over 2000 psi to start. I would try capping injectors one by one until I found the one causing the no start.

 

Still, unplug the FCA and see if it helps. So easy to do ...