Crazy rail pressure issue- too high and too low.

[Tinman]

For months now I've had a problem with very intermittent lose of rail pressure. Running a Optix gauge. Only at steady state, idle or cruising, I will lose rail pressure for a second or two with corresponding lose of power. Otherwise, truck runs great. It is getting more frequent and now will do it at idle daily. Once, at idle, it completely stalled. Here is the weirdest and scariest event: About a week ago, I was at a stop light with a cold engine. All of a sudden, the engine sounded like my single injection event tune. Rail pressure was idling at 25K. Once the light turned, I eased off the road. Adding throttle raised rail pressure to near 30K. I shut it down and cranked it back up, ran fine. Since this has all started, I have replaced, FCA (twice), cascade valve, rail pressure sensor and pressure relief valve, and removed Optix gauge from circuit. None of this has made any difference. What next??? CP3????. Oh yeah, injectors replaced a few years ago and have less that 100K. Motor has just over 200K. Never any codes except when pressure spiked.

 

[jgillott]

Check the wiring harness coming off of the rail pressure sensor. I had an issue with rail pressure spikes on my '07 years ago and it ended up being the harness itself and not any hard part.

I don't remember now off hand how we discovered that it was the problem, but I remember it getting to the point where it was almost undriveable.

 

[Tinman]

What about the FCA wire plug?? I see Geno's sells a plug repair kit. That makes me think it is a common issue to fail.

 

[Tinman]

So I have figured out the spike in rail pressure was a loss of signal to FCA. If you unplug it, it will do the same thing indicating the FCA is working and in my case a spontaneous lose in signal. With the engine running, I can't move the wires around or put tension on the plug to reproduce any symptom which I would think would be likely if there was bad wire or connection. I don't think this is a hard part problem but a sensor or wire issue. I just don't know what is the next step??? Should I consider replacing MAF, MAP sensors. The wiring harness for the engine is all one piece and cost $1300.

 

[jgillott]

You could swap out the other sensors first I guess. I just hate to see you throwing parts at it though until you narrow it down.

I also can't in good conscience tell you to buy a $1300 engine harness. With my harness issues, I simply went to the local junk yard an cut the rail pressure sensor connector and the short harness back to the bundle off and spliced it in to my existing engine harness. The FCA connector sold by Geno's is the same process if I'm not mistaking.

I know this process is extremely frustrating. Believe me when I tell you that if there has been a 3rd gen electrical issue possible, I've had it with one of my trucks. In the end, I'd really try to identify where the issue is first and then simply splice in the new connector if that is what you need.

 

[Tinman]

That makes sense. I'll try the Geno's FCA connector first. Cheap and easy. With no codes and the spike in rail pressure, it has to be a problem with the FCA circuit. Question is where.

 

[Tinman]

Update. I replaced the FCA connector and for several weeks it did just fine. But, sure enough, it is doing it again. I have read more about this and for all the world it acts like a bad FCA. But I have put on 2 or those, one brand new. Placed RPV also. Can a bad CP3 even do this.

 

[eastmentCTD600]

I don't know if it's too late to post here but I had some weird issues with rail pressure. My Rail Pressure Sensors was actually physically damaged. The plastic body was displaced at a slight angle from the metal base. Replaced it and it corrected several issues including random no-start condition or engine cut-out while driving.

 

[Tinman]

I replaced sensor early on in the process. About a month ago, I put in another RPRV and all was good for about a month. Then all of a sudden really bad problems. Erratic rail pressure, missing, etc. I removed the rail pressure gauge from the circuit and it has been perfect ever since - about 2 weeks. So I now know it is a wiring issue. I'm not yet convinced it's the gauge as I removed the gauge as one of the first diagnostic and therapeutic measures. It could still be the factory wiring harness, but I'm go without the gauge for a bit and see.