Also if it is a defective one why add the LBZ one? Also would adding a race/delete valve be a better solution for the relief valve??
Last edited:
LB7: Replaced FPRV now has loping idle
- Thread starter 20chevy04
- Start date
You could have other worn parts in the fuel system, insufficient supply to the cp3, or an electrical issue such as a loose connection. Either way you might be best taking it to someone who is more experienced in duramaxes.
Not to high jack the thread, but I'm having some of the same issues. I just changed my fpr yesterday, and I'm still having the same lopey idle, and fuel knock. Changed fuel filter on motor, and still no fix. While I was in there, I took out my fprv shim kit since I had the parts to do so, and since I was right there. I got three codes from the cel being on, P0088, P0089, and P0090. I'm hoping its not a bad fpr, even though I've read what everyone has said about being new and no good. Any thoughts on maybe a rail pressure sensor going bad? Thanks..
Double check that all three torx screws to the fpr are tight. Also, check your line pressure coming off a lift pump if you have one. I had an issue with a truck running two 220gph fass pumps, one of the pumps broke the internal spring that regulates line pressure causing it to pressurize the fuel line past 9psi, where it starts to effect fuel rail pressure. When the pump would be turned on it pushed rail to 14k psi at idle, started rattling and loping too.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Iirc do trucks go to full rail if the Fuel rail pressure sensor is unplugged?
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
LBZ fpr is used on older trucks to command a higher rail pressure than the LB7 regulator will allow (over 24,000psi I believe).
As far as the fprv, most people shim them so it wont "pop" open as easily.
As far as the fprv, most people shim them so it wont "pop" open as easily.
If you want to do this yourself, as stated, check your supply pressure post filter, lbz isn't as finicky with higher feed pressure but do it to rule out low pressure/possible air contamination. Then log your desired vs. Actual rail pressures and desired vs actual fuel pressure regulator currents, making sure they correlate within a few hundred psi at no engine load. Your rail pressure will most likely be close to 5500psi at idle in the stock tune. If your supply pressure to the pump is good and your actual rail pressure is high and not changing much, there is a good chance your regulator connector harness has an open circuit. If rail pressure is really low, but supply is good, you either have a high pressure fuel leak caused by human error or by faulty components, or you may have a bad rail sensor. When logging the fuel system, also make sure to note proper ect, iat, fuel temp, and map values
Race valve or shimming it accomplishes the same goal. When people use a race valve it deletes the valve that relieves the pressure when it gets too high. When they shim it, your just modifying the stock valve, increasing the pressure that is required to open the valve. Iirc even a shimmed valve doesn't open if a cp3 is commanding max rail.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Yes it was a faulty FPR. Even though they are new in box like the others have said it was bad. Thanks for all the help hope the next one is good