LB7: Unusual high rail pressure issue.

[Drew92]

We recently picked up an 03 duramax that was having high rail pressure issues when we picked it up. We got the truck back to the shop, changed the regulator, cleared the codes, and is still idling around the 23,000psi mark. Here's where it gets weird; no codes came back. We then thought that the ECM was bad, so we replaced it as well with no luck. Figuring the new regulator was bad, we chose to switch with another new regulator- same thing. Started testing voltage, and it runs ~1 volt at the regulator with just the key on. As soon as you start it, it goes down around 0.05volts. Thinking it was maybe a wiring issue, we jumped the wire from the ECM straight to the regulator, still same thing. Tried testing voltage with a spare cp3 just sitting on the top of the engine and it still drops volts. Tried switching the FICM as well with no avail.

When driving the truck, the rail pressure constantly stays at 23000 or whatever it is, no matter what the desired is.

This has my mechanic and I both stumped, so I figured I would look here for advice. Let me know if you have any questions or suggestions.

Thank you
-Drew

 

[Kappa9012]

are you sure the sensor isn't bad? have you measured actual rail pressure to see if 23,000 is the real pressure. If you're at idle that high of rail pressure should sound horrible.

 

[Chevy1925]

bad wire thats suppose to feed the voltage to the reg would be my guess. it needs voltage to keep rail pressure down. with no voltage it goes wide open

 

[Kappa9012]

I was thinking the same thing, but he jumped from the ecm to the reg.

 

[Drew92]

It sounds absolutely terrible! My mechanic is pretty sharp on this stuff and him and I are clueless at this point. I figured it would try to even out when you started to drive it, but it stays the same. Even at WOT actual is higher than desired.

 

[Chevy1925]

whats the voltage coming out of the ECM?

 

[Kappa9012]

ok so the bad sounds tells me the rail pressure is actually high, not being a jerk, but are you sure you got the right pins on the ecm? It really sounds like the ecm is not seeing the regulator.

 

[Drew92]

It wouldn't make sense that its getting any voltage at the regulator if there was an issue with the pin.

 

[Kappa9012]

a short to ground can drag the voltage down