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7.3 PSD running on 4 cylinders


That is def low. Not even gassers will run well at 21 psi.
 
what year?


sure its not the cps?


air bubbles in the fuel? mech or electric lift pump? fuel psi at the head was 21 psi from the lift pump? cant be that high iirc



sometimes the bypass valve in the tank hangs and airs it off, usually pull the filter cover refill and it will run till it airs off again...one way i test for mech pumps
 
the air off occurs below 1/2 tank...so if its full its not something to put at the top of shit to look at....

if its an electric lift pump i am sure they run 50 psi plus my mech runs 9 last i checked it but maybe its supposed to be 21 or more.


assuming you looked to make sure the filter lid isnt cracked or the o ring bunged up or something.

i have had the feed line crack on mine and air me off as well. i have a mech lift pump obviously
 
what year?


sure its not the cps?


air bubbles in the fuel? mech or electric lift pump? fuel psi at the head was 21 psi from the lift pump? cant be that high iirc



sometimes the bypass valve in the tank hangs and airs it off, usually pull the filter cover refill and it will run till it airs off again...one way i test for mech pumps


I don't remember what year his truck is, but he has a turbo and an IDM, which means it has HEUI style injectors that create injection pressure with high pressure oil.

EDIT:

Here is Ford's description of the fuel pump operation:

Fuel is drawn from the fuel tank (9002) by the diaphragm section of the fuel pump (9350). The fuel pump circulates fuel at low pressure (approximately 21-69 kPa [3 to 10 psi]), first through the fuel filter (9155) and then back to the second stage of the fuel pump.

During the second stage, the piston-actuated section of the fuel pump supplies fuel at a pressure of approximately 275 kPa (40 psi) into the cylinder head fuel galleries.
 
Last edited:
I looked it up and 20 psi is about the minimum acceptable crank pressure. Idealy it should be 25-30 psi, but should still start as low as 20. Thats not to say the pump isnt the problem because the original symptom was that it would start and run normally for a few seconds before the rpms dropped and it started sounding like someone running a jackhammer on a bank vault, just before dying. From what i have found that is a symptom of low fuel pressure. Could be the pump ($150 sitting on the shelf at o'riellys) or the fuel pressure regulator ($230 on the same shelf at the same store)

I need to do some more troubleshooting when the sun comes back up. And contrary to most military manuals blind parts replacement is not an acceptable diagnostic procedure!
 
Oh and its a '95. I thought that was already in here.....
 
All the troubles I've ever had with diesels was air in the system. What bit do the electronics control on a '95 Powerstroke? Even on a gas motor I would not go straight at the electronics to find a fault. It's usually a mechanical issue.
 
All thats directly controlled electronically is fuel injection, however everything is monitored electronically. If the oil temp, level, or pressure is out of range it will shut down. If a single injector faults, it will shut down. If fuel pressure is out of range it will shut down. It has a circuit to test the tps, if im standing on the skinny pedal and the idle validation switch says otherwise, it will drop to idle. These things are a little over engineered.

Normally i would start hunting mechanical problems before looking into the electronics, the diesels i grew up on didn't have brains, the didn't need them. This thing is nothimg but a big damned paperweight without all the electrical crap controlling it, that and the fact that i had strikingly similar symptoms last year that were caused by a faulty piece of electronics, i can't help but think its an electrical problem.
 
well, the regulater housing deal or the pump--pump feed restricted-- is a likely culprit with the 20 psi....

i know both can cause the pressure issue. i would bypass the mech pump in the valley and force feed 40 regulated psi to it and see what it does....she goes vrooooom gar gar gar gar gar its a fuel issue for sure....


whether its a pump laying down, bad regulater-regulater housing, or airoff/blockage in tank is a whole different set of shit to do. maybe its just an algae turd in the tank or something....maybe theres 20 gallons of water in it:dunno:
 
21 psi is not great but it should start and run. Have a scanner ? What does the ICP say ?
 
maybe theres 20 gallons of water in it:dunno:

That's about normal this time of year.


Maybe the cetane isn't high enough for the weather. Does it get better or worse as it warms up.
 
Haven't managed to get home from work before dark so far this week, George is just gonna have to wait till the weekend. Thanks for the input everyone!
 

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