High rail pressure, erratic idle

ThunderedRod

ThunderedRod

Hot Pants
Joined
Mar 13, 2012
Messages
152
It all started two days ago was driving the truck when rail pressure spiked to 30k for 5-10 seconds, then back to normal for 5-10 seconds. The truck did this 4 or 5 times back and forth. I pulled over pulled the smarty tune out and entered a stock tune. The issue continued, high rail pressure for 5-10 seconds then back to normal of 6-7000. I shut the truck off and thought about what to do. Started the truck about 10 mins later and it magically was running great! No issues. I drove it home and drove it the next day about 30-40 miles.

Today I returned to my truck after lunch, started it up and high rail pressure again and knocking that comes with it. This time however it was not intermittent like before. I played with the cp3s connectors to make sure all where good and connected right. No change.

While it was running I unconnected the top pumps FCA and there was no change. I then unconnected the bottom pumps FCA and the idle got worse. So I figured it was the top pumps FCA.

I'm also getting some strange codes with this issue. All of the codes appeared when I removed the bottom pumps FCA connector. All the codes started when I disconnected the bottom FCA.

After I hooked everything back up the idle is so awful the truck barley runs and has erratic idle and white/black smoke. Sounds like a timing issue.


DTCs
Water in fuel.
I have the stock fuel bowl removed from the truck so this seems very strange.

Cp3 pump regulator control, map sensor voltage too low, sensor reference voltage 2 circuit low and accelerator petal position sensor 2 circuit low.

I tried replacing the FCA with a known good unit. Didn't fix anything.
I also tried disconnecting the rail pressure sensor. This actually returned the truck to a better idle but far from good or drivable. Rail pressure too high and those 5 codes.

Tomorrow I'm having a friend drop off a known good rail pressure sensor to try out.



Help!! Any ideas???

What are the syptoms of a bad rail pressure sensor?
 
your sig says stock cp3 but you have 2 pumps? whose cp3's and who made the harness splitter?

yeah peter.....the year of the truck would be greaaaaaaaaaaat.

normally that is a bad FCA/ wiring
 
Pull the belt and bypass the upper cp3 and controller. Plug factory plug into bottom FCA and see how it does.
 
I am having similiar problem. I have replaced both FCAs, RP sensor, unplugged autometer rail pressure gauge, have truck hooked up to a snap on scanner, new dual cp3 controller, new injectors new top cp3, 30k miles on bottom cp3

Starts up fine but the rail pressure at idle fluctuates up and down 4000 psi like 4k to 8k 5k to 9k. Took smarty off and still same problem.
 
SixOhh said:
your sig says stock cp3 but you have 2 pumps? whose cp3's and who made the harness splitter?

yeah peter.....the year of the truck would be greaaaaaaaaaaat.

normally that is a bad FCA/ wiring
Click to expand...


2005

Sorry, it's a dual cp3 kit I bought from Kai Zimmerman. It uses a ATS controller. The top pump is a stock used unit I got off a guy on cummins forum. I installed it in January off this year. The top pump had a bad FCA when I installed the kit. Everything ran excellent till yesterday.

Also I've contacted Allen Cook at Ats and he is looking into getting me a replacement controller.
 
Last edited:
Bypassed the top pump, moved the pressure sensor to stock location and it runs great! Thanks guys!
 
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