Question about 6.7 rail pressure...

weazel

weazel

5th gear killer
Joined
May 14, 2008
Messages
2,252
Ok I have a question on the 6.7's rail pressure, along with using a smarty and a TS MP8.. driving down the road, the truck runs great and fuel mileage is good too. My problem comes when I go to pass someone, and I go to return to normal speed, the truck will throw a check engine light, and the catalyst full message comes on on the overhead display. When I check codes with smarty, it says the fuel relief valve has been activated.

I barely have the mp8 turned up, and I'm running sw7, timing 2, rail pressure 1, torque management 4, and turbo on 4. Why does the truck keep throwing the code?
 
weazel said:
I have left that stock..
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there is your problem then, shim it then you should be fine, the pressure increase from the smarty and mp8 exceeds what the relief is set at, or it could be getting weak and pooping off even lower, my mp8 up all the way will increase my rail pressure 6k 3at wot, I run 30k rail pressure and have yet to throw the code for popping open the relief valve, but mine is shimmed.
 
Ok, thanks for the replys! I'll get it shimmed as soon as I can!
 
shim it or plug it, same effect... you'll be amazed at the power you pickup by not having that thing pop open
 
the cat full code has nothing to do with the reilf valve does it i have experienced the same with a smarty and have no issues with h&s and a mp8
 
reed6.7cummins said:
the cat full code has nothing to do with the reilf valve does it i have experienced the same with a smarty and have no issues with h&s and a mp8
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That code shows its face with a low rail code almost every time. The Smarty pops a code for a reason........... It makes more power. If its not popen the relief valve its not calling for the fuel needed to make it!!!!!!!!!!!!!!
 
What about using a dual feed line? I thought about one of those the other day. I have one left over from when I had my 5.9 CR..
 
5.9 dual feed won't work on 6.7, the rail and high pressure plumbing is quite a bit different. The 6.7 lines are much larger and can carry all the fuel you need for plenty of power... just plug the relief.
 
Ok got a ppe plug installed. The truck runs really nice now! Best part is I don't get codes thrown, and no more limp mode!
 
Cummins engineers put the relief there for a reason. What's it's purpose? If we plug this relief, do we risk anything else failing? Any side effects?
 
XLR8R said:
Plugging the rail = :badidea:
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agreed, not to mention the 6.7 has plenty of rail pressure without adding any more in the mix. If you are competing or on the dyno then go for it but for daily driving and playing around I wouldn't$.02
 
shim the valve and wait for tuning with better control of rail pressure, keep that mp8 turned off unless you need it
 
When you shim it increases the pressure it takes to open. Plugging it prevents it from opening at all (as mentioned above bad idea) you rush more serious damage by plugging it
 
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