Manifold Absolute Pressure

**DRD** · 09-22-2014

H&S 4th Gen 6.7 tuning caps the rail pressure at 26100 psi at full tilt. From my experience with 4th gens, you're not going to get it over 27500 psi with even with MCC. 3rd Gen 6.7's are a whole different ball game.
I've hit 27500 psi with my 2012 and never popped the relief valve. With the street duration, she'll make 24-25 KSI depending on strong your CP3 is. The performance duration will drop it down around 22 KSI at full tilt. The reason these durations won't allow the commanded 26100 psi is that they are simply too much for the stock CP3 to keep up with.

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**Calibrated Addiction** · 09-22-2014

I hold 24k on my performance setting. the 4th gens don't seem to have as much issue with the PRV popping like the 3rd gens did. however id did notice shimming mine helped with the pressure at wot on higher duration tunes

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**Gsxrgrizz** · 09-22-2014

So it sounds like monitoring the fuel rail pressure, while a great diagnostic tool for me to use, is not really super important outside of major mods to my truck.....am I in the right track?

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**DRD** · 09-22-2014

Originally Posted by Gsxrgrizz

So it sounds like monitoring the fuel rail pressure, while a great diagnostic tool for me to use, is not really super important outside of major mods to my truck.....am I in the right track?

Yes you are. Later down the road it can be very important to monitor. For now, if it dropped too much, you would get a CEL with a low rail pressure code.

Keep a good fuel filter on your rig and ride on.

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**Dieselbowhunter** · 02-12-2015

My cts does that to me in my 09 every once and awhile when I get on it. Worried me at first but after talking to some guys doesn't really seem like a big deal, I didn't turn it off I just ignore it.

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