high rail pressure on shutoff. Cause for concern?

[tjm]

Either this has been going on all along or I just noticed it.

 

[AH64ID]

Normal, as the CP3/FCA loses voltage the pressure spikes to max and the PRV keeps it from going too high. This is one of the reasons PRV blockoffs are a bad idea.

 

[tjm]

Normal, as the CP3/FCA loses voltage the pressure spikes to max and the PRV keeps it from going too high. This is one of the reasons PRV blockoffs are a bad idea.

Thanks John!

 

[Grumpy8811]

was going to offer that isn't even hi rail pressure.. as it is below what the rail pressure relief valve opens at..
plus its just a spike when shutting down and relieves itself in seconds.

 

[AH64ID]

was going to offer that isn't even hi rail pressure.. as it is below what the rail pressure relief valve opens at..
plus its just a spike when shutting down and relieves itself in seconds.

That's high rail pressure on a 03-07 5.9, the max commanded is 23,206 psi (unless it's tuned for higher) and the PRV opens at ~26K psi so he's right there based on the refresh rate and how quick pressure drops at shutdown when the PRV opens.

 

[Grumpy8811]

That's high rail pressure on a 03-07 5.9, the max commanded is 23,206 psi (unless it's tuned for higher) and the PRV opens at ~26K psi so he's right there based on the refresh rate and how quick pressure drops at shutdown when the PRV opens.

I was under the impression the CP3 pump could produce over 2000 bar... commanded fuel rail pressure is generally lower than that and obviously once the actuator loses signal he is just seeing a pressure spike in the process of the engine shutting down. either way it isn't 2000 bar... which would be close to 29,400 psi

 

[AH64ID]

I was under the impression the CP3 pump could produce over 2000 bar... commanded fuel rail pressure is generally lower than that and obviously once the actuator loses signal he is just seeing a pressure spike in the process of the engine shutting down. either way it isn't 2000 bar... which would be close to 29,400 psi

The CP3 can, and does in my 2022 with stock programming. To run over 26K psi in an 05 takes some work, such as a higher pressure PRV.

I don't have my tuning computer with me, but IIRC the limit for tuning the 5.9 is around 26K with the OEM sensor... but it's been a while, so I'd have to look.