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Old 05-07-2013, 04:43 PM
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Question Trying to determine if my HPOP is going bad

Been having a lack of power problem with my late '04 truck.

Starts well cold or hot, but seems very flat much past 1/2 throttle, it seems to get worse as the engine warms.

Some HPOP and IRP reading as follows

Idle HPOP 580 PSI IPR 24%
Light Accel HPOP 1400 PSI IPR 45%
WOT HPOP 850 PSI IRP 83%

Right how I am not understanding the fall off in HPOP pressure at WOT, anything else I can look at to narrow down a bad HPOP or maybe a bad IPR?

No codes in the system other than some glow plug codes on the passenger side that I have yet to look at.

Recent EOT/ECT delta have been running at 20 degrees, so an oil cooler replacement is in the cards, would love to be able to fix the lack of power problem at the same time without throwing unneeded parts at it.

Any ideas of what else to look for?

BTW: I have learned so much about my 6.0 from reading this forum, incredible amount of knowledge and experience here!

Last edited by DonLCNY; 05-07-2013 at 04:53 PM.
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Old 05-07-2013, 05:14 PM
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I would suspect a HPO Leak or a weak HPOP. Was the Idle ICP pressure after the truck was hot? Typically a leak and or weak HPOP will cause the IPR reading to start climbing after the truck is hot, because the lack of pressure reading from the ICP causes the IPR to try and compensate by staying closed longer. The 03 and 04 HPO branch system is much more robust on our trucks versus later models with the SCT. The typical known failures on our 03 and 04's is the HPOP, the HPOP Discharge Tube (some tubes rub the cover and cause a leak, mine did), and the braided lines that go from the block tube to the oil rail on the injectors. The o-rings on the oil rail sometimes go bad and leak, but its not as common as the others. Oh, theres another HPO o-ring on the injector too, again less likely to cause problems, anything is possible though. A check of the ICP and IPR readings when the engine is good and hot will render a lot of info. Check that ICP sensor out good too, they tend to leak oil through the connector and screw things up by sending false readings.
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Old 05-07-2013, 05:36 PM
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All reading where good and hot, in fact just got done pulling 8,000lbs of logs, I think ECT was 196 and EOT was almost 220.

I have tried an air test in the past which was inconclusive in my mind. But went ahead and installed updated dummy plugs and standpipes, as well as replaced all the o-rings on the HPOP itself.

Did not see any signs of the branch tube rubbing, although the fitting seemed loose, from other posts regarding this this seemed normal.

ICP Sensor did not show any signs of oil leaks.

I am still confused by the lower HPOP pressure at WOT and higher ICP duty when compared to light acceleration. I would seem like if there was a HPO leak, then WOT HPOP oil pressure should at least get to the 1800 PSI of light accel, but it actually drops down from 1800 to 850 just stepping on the pedal. Might be I am just confused on the relationship of IPC duty and HPOP pressure.
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Old 06-17-2013, 10:33 AM
DBM DBM is offline
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I think the readings show, as said, an HPO leak or weak HPOP. The reason the HPO pressure is lower at WOT is it can't keep up with the demand. the IPR is closed (or near) at 85%, so at WOT the IPR is trying to get the pressure up but can't due to leak or weak HPOP.
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Old 06-17-2013, 11:03 AM
DBM DBM is offline
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also, if your temps were ECT 196 and EOT was 220 while pulling 8000 pounds, I would guess your oil cooler is ok, the 15 degree spread is running ~65 on flat highway for ~20 minutes unloaded...
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Old 06-17-2013, 01:38 PM
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Update!

Quote:
Originally Posted by DBM View Post
I think the readings show, as said, an HPO leak or weak HPOP. The reason the HPO pressure is lower at WOT is it can't keep up with the demand. the IPR is closed (or near) at 85%, so at WOT the IPR is trying to get the pressure up but can't due to leak or weak HPOP.
Thanks for the reply, I should probably update the fact that the problem was in-fact a weak HPOP, once the new pump was installed, my truck is a totally different truck and running great.

Still don't quite understand how the whole HPO system works and why the reading where as reported, but I am sure glad I found the cause of the problem.

Thanks all the for the help, and the great forum.
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