my car is in limp mode saying reduced engine power does anyone know what the proper fuel pressure is suppose to be at idle for the lnf? im tuned im not sure if it gets changed for that

from searching around im pretty sure its something to do with the high pressure fuel pump either the pump its self or the connector getting stretched and wires pulled apart the connector that goes into the hpfp where is the other end of it go so i can meter it through end to end? then ill know if i should replace the pump

 

you should have one of these codes if there is an issue with the hi pressure pumo
DTC P0087, P0088, or P0089

DTC Descriptors
DTC P0087
Fuel Rail Pressure (FRP) Too Low
DTC P0088
Fuel Rail Pressure (FRP) Too High
DTC P0089
Fuel Pressure Regulator Performance

if its the fuel pump itself, get a good multimeter, and check as follows:
Static Test
1. Ignition OFF, disconnect the harness connector at the high pressure fuel pump.
Note: The DMM and test leads must be calibrated to 0 Ω in order to prevent misdiagnosis.
2. Test for 0.35–0.6 Ω at 20°C (68°F) between low control circuit terminal 1 and high control circuit terminal 2.
⇒ If the resistance is less than 0.3 Ω or greater than 0.6 Ω, replace the high pressure fuel pump.
3. Test for infinite resistance between each terminal and the high pressure fuel pup housing/case.
⇒ If not the specified value, replace the high pressure fuel pump.

Its unlikely you have a fuel pressure tester that has the 400 psi or greater capacity to check fuel rail pressure. So the static test makes more sense. Good luck,

 

A LNF in limp mode is not always directly related to the fuel pump. Check the CELs that set, that will tell you the issue.

If you have the codes Powell listed then try the procedure he outlined to make sure that's the issue.

 

i meant to say i do have p0087 and p0089 im going to test with a multimeter now

EDIT: just tested between terminal 1 and terminal 2 got a constant .4 ohms-.5ohms and tested each terminal to the housing its self and each terminal stayed at OL (over limit) so does this mean the high pressure fuel pump is fine?
also metered the connector on the hpfp back to the ecu connector pins 5 and 73 both ring out so they are not broken

what is the lnf fuel pressure at the rail?
and is there a sensor somewhere that tells the car its fuel pressure that i could possible test?

 

If you have hptuners or the torque app (not 100% on torque app) you can read the fuel pressure.

 

At idle anywhere from 200-400 psi is where it swings around between

 

If the resistance is less than 0.3 Ω or greater than 0.6 Ω, replace the high pressure fuel pump.So you have done the tests, the high pressure fuel pump is fine.
Diagnostic Aids:
A skewed fuel rail fuel pressure sensor may set these DTCs. A faulty fuel injector can set a p0089.
I would look at the sensor its easy to damage it sits on the end of the fuel rail and is fragile. The fuel injector kit is a pita to rebuild the injectors/ If it was me I would buy a fuel rail and injectors stock take off in as new condition from either Mongo rat or ZZP. If you feel adventurous, get the injector kit. You will need an inlet manifold gasket, and you might as well clean the valves and replace the pcv valve while the inlet manifold is off and before you remove the fuel rail. Go in and do it right once. You dont have to walnut blast the valves, GM top end cleaner some wipers and a vacuum will do its more work and dirty that way but you dont need an air compressor. Either way its a long weekend of work.