I was doing some data logging the other day and I noticed a few things. My desired pedal position and actual match pretty closely, and my fuel pressure desired and actual are within 2MPa of each other, but my FPR duty cycle is always 20-40% throughout the RPM range. Is this normal? I’ve also noticed if I unplug the FPR my fuel pressure does not go to full rail, but something like 14KPSI.
Normal FPR duty cycle?
- Thread starter Trgglynn
- Start date
That's definitely not normal. You should be at full rail pressure with the FPR unplugged.
Just wondering if this is an lly thing. I did some work on my Kodiak (lly) and forgot to plug the fpr back in. When I realized what I did, the desired and actual were only at 9,500. Should the desired read 23,206 if the fpr is unplugged? Truck has no problem building and holding 23k while driving.
I could be wrong, but I believe the FPR regulates fuel via adding voltage to restrict fuel, and that is why it goes to max pressure when the power is disconnected.
I have this CP3, about two years old.
LDS LBZ SuperStock CP3 Pump
Fit: 2001-2016 GM/Duramax LB7, LLY, LBZ, LMM, LML
When I unplug the FPR when the engine calls, it desires 42MPa and actual sits at 85MPa.
I just changed out the regulator with a new Bosch unit, as well as replaced the pigtail going to the FPR. I am getting 160MPa desired and actual is 158-160MPa. Still am getting about 2300RPM in fifth gear to about 50MPH and then it will downshift if I give it any more than 1/4 throttle or so to get any more speed. The fuel pressure seems to be tracking within a couple MPa at all times.
The duty cycle of the FPR at idle is about 38%, and at WOT is 25%. Shouldn’t this drop near zero at WOT? And shouldn’t it command full unplugged??
Funny enough after flooring it around I just got a P0089 “FPR Perfomance”. I’m pretty sure the regulator itself is good. I did a bottle test recently and got no leakage. As my last FPR did about the same regarding pressure and this one is less than a month old. I think it may just be what the ECM is calling for for some reason, or something effecting the ECM commands… maybe the injectors do leak and bleed off pressure or something.
Are you running a lift pump that is turned up a little high? P0089 if often from too much pressure and the regulator can't pull it down enough to match desired within the tolerance value. Sticking regulator can do it too
Also, command of the FPR regulator is based on the tune. A stock tune I don't think allows 100% or zero if you look at it from the voltage/current prospective. Amd unplugged it will only change it as far as the PID controls will allow, and that is based mostly on the fact that it's going to get a lot more pressure then it's expecting based on the tune tables
Also, command of the FPR regulator is based on the tune. A stock tune I don't think allows 100% or zero if you look at it from the voltage/current prospective. Amd unplugged it will only change it as far as the PID controls will allow, and that is based mostly on the fact that it's going to get a lot more pressure then it's expecting based on the tune tables
This may not exactly answer your question, but it may help understanding the problem if there is one.
The fuel pressure is electronically controlled by the Fuel Rail Pressure Regulator (FRPR). The
FRPR is a duty-cycle solenoid mounted in the pump and controlled by the Electronic Control
Module (ECM) based on feedback from a sensor in the junction block that provides fuel to the
supply rails. The FRPR duty-cycle operates in a 5 to 95 percent window, and unplugging the
solenoid drives the fuel pressure to the maximum level instead of vice versa, as we might expect.
The ECM increases pulse width to lower pressure, so if the solenoid receives a 100 percent dutycycle for some reason, pressure will be at its lowest, and performance will obviously degrade. A 5 percent duty-cycle will produce a fuel pressure of 23,200 psi, and a 95 percent duty-cycle feed will produce a 5,000 psi reading. The pressure should never go below 3,000 psi; if it does,
something is wrong. The Tech 2 scan tool provides target and actual fuel pressure readings for
diagnostic purposes.
The fuel pressure is electronically controlled by the Fuel Rail Pressure Regulator (FRPR). The
FRPR is a duty-cycle solenoid mounted in the pump and controlled by the Electronic Control
Module (ECM) based on feedback from a sensor in the junction block that provides fuel to the
supply rails. The FRPR duty-cycle operates in a 5 to 95 percent window, and unplugging the
solenoid drives the fuel pressure to the maximum level instead of vice versa, as we might expect.
The ECM increases pulse width to lower pressure, so if the solenoid receives a 100 percent dutycycle for some reason, pressure will be at its lowest, and performance will obviously degrade. A 5 percent duty-cycle will produce a fuel pressure of 23,200 psi, and a 95 percent duty-cycle feed will produce a 5,000 psi reading. The pressure should never go below 3,000 psi; if it does,
something is wrong. The Tech 2 scan tool provides target and actual fuel pressure readings for
diagnostic purposes.
Thank you for that! I appreciate the information.
Also, I ran a diag procedure off of the P0089 pdf you posted and my rail pressure sensor reads 180 MPa unplugged, so according to the diag step 7 I need to replace the rail sensor? I did skip step 6 because i didn’t have a computer handy at the time to manipulate the fuel pressure.
I do have an Airdog 150 that’s putting out 11 PSI last I checked. It doesn’t lope at idle. It has some weird idle inconsistencies, but I don’t think it’s the high pressure lope.
I’m curious, with the regulator unplugged does the ECU have any means to reduce the pressure?
Attachments
Keep in mind that the attachment came from an LMM and I don't know what a similar document for your truck would show. 26K lbs is a lot of pressure. It certainly wouldn't hurt to change the sensor. I think I would hold off until you get your problem sorted out before changing the pressure sensor if I were doing the work
Thank you for this!! Very helpful. I believe the sensor in the junction block may be my problem. Any idea as to what sensor that is?
Ah ok, thank you for the heads up. It seems like whatever is driving the ECM to control the pressures is part of the problem.
I checked my balance rates again today, and they are not too great. Checked compression on #5 and #6 again with a new compression tester, and tested 390 and 400 respectively. Early today cylinder 6 was at +3.5ish balance. Injector 2 and 4 are new Bosch injectors from Diesel Power Products. I am leaning toward the electrical side being wrong somewhere, or a bad FICM still. Probably in conjunction to the pressure issue.
Attachments
Not really. Here is a link to the entire publication that copied. https://www.google.com/url?sa=t&sou...oQFnoECBQQAQ&usg=AOvVaw0PKd68eM4rhRcGOj5zBEL1
You are missing something because the truck sets the P0089 code when actual and desired are off by more than 20 MPa. You need to datalog it and figure out where it isn't maintaining desired rail pressure.
Were you directed to step 7 by another step, or were you just going down the list? You need to start at 1, and proceed step by step following the diagnostic tree depending on the result of each test. If you just skipped 6 and went to 7, you did an improper diagnosis.