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I got my hpop pressure gauge hooked up and took a quick trip around the neighborhood.
It took a lot of cranking to start the engine.
Reads 0psi while cranking. Tried this multiple times with same result.
Once running psi jumps to 300 then builds to 600 over about 2-3 sec.
Holds 600 at idle.
Step on the throttle and it holds 600 to 1500 rpm then quicly builds to 2500 at full throttle.
Holds 2500 at full throttle but instantly drops to 600 if I back out of the throttle even 50 rpm.

Its as if can put out 2500 psi but doesn't have the volume to drive up the pressure.

ICP has new O-Rings, Injectors are re-man. Problem was worse before these were done so I must be getting close.

Diagnosis???
 

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If you had air in the hose to your gauge, it probably would require time to compress it. If you carefully bleed the air from the line, it should start as it normally would.

The following is from dieselmans site. I gives the methods for diagnosing high pressure issues. I have removed a portion reguarding newer models connectors(not needed). And added where I thought I could clearify.

By using adapter fittings and plugs you can isolate and measure each cylinder bank to see if there is a high pressure oil leak in one head, or connect both HP oil pump hoses to the pressure gauge to measure pump pressure. (isolated from engines high pressure galleries)

If isolated pump pressure is low, short break-out-box pin 83 to ground to run IPR valve to full duty-cycle. If the pressure comes up (3600 psi) replace the PCM; if it remains low, remove and inspect the IPR o-rings for damage; a kit is available if they are. If the IPR o-rings are undamaged, replace the IPR valve. If there is still low oil pressure, replace the HP oil pump.

(once you determine the pump is ok and can build the pressure, you can isolate each head to see if one or the other has a leak. testing the left bank requires moving the IPC to your test gauge manifold.)

If isolated HP oil pump pressure is 500 psi, or only one bank reads low, remove all the fuel injectors and replace their o-rings using the latest kits P/N F8TZ-9229-AA.
If the concern is a jerky, irratic idle when hot, unplug the ICP sensor (will set a code, causes the PCM to default to a pre-selected IPR duty cycle) to see if it the idle stabilizes. If it does, check the ICP voltage with a scan tool or breakout box at pins 87 to 91 with the sensor plugged in and the key on/engine off. It should be .20-.25 volts. If the base ICP voltage is within specs, replace the IPR; If not, replace the ICP and retest.

I hope this helps.
 

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I got my hpop pressure gauge hooked up and took a quick trip around the neighborhood.
It took a lot of cranking to start the engine.
Reads 0psi while cranking. Tried this multiple times with same result.
Once running psi jumps to 300 then builds to 600 over about 2-3 sec.
Holds 600 at idle.
Step on the throttle and it holds 600 to 1500 rpm then quicly builds to 2500 at full throttle.
Holds 2500 at full throttle but instantly drops to 600 if I back out of the throttle even 50 rpm.

Its as if can put out 2500 psi but doesn't have the volume to drive up the pressure.

ICP has new O-Rings, Injectors are re-man. Problem was worse before these were done so I must be getting close.

Diagnosis???
Pick up the riffraff fuel return kit, it eliminates the air in your lines, quiets your engine and it will run better as well. Your HPOP should build psi quicker and you should be above 2500 @WOT. Sounds like you need to rebuild it. I read somewhere that only 5% of 7.3's have an HPOP that's up to snuff causing from mild to wild symptoms. Mine was talking flat on it's face after 2000rpms. Like I was hitting a limiter. Changed the up pipes and some other stuff before figuring out it was the HPOP.
 

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After 12 years, he probably got it figured out.
 
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