DamageINC Posted January 25, 2010 Share Posted January 25, 2010 What's up fellas? I have an 06 E-450 U-haul truck here, with a P0191 in memory and CEL on. It's the "fuel Rail Pressure Sensor" performance code... now I'm well aware of the SSM that mentions to inspect the tank and pump for signs of metal contamination in aft-axle fuel tanks, and that pump and tank replacement may be necessary. In this case, I removed the pump and inspected it thoroughly. There was a magnet in the tank, much like a trans pan magnet, and it is pretty hairy looking, lots of metal shavings and some larger debris (almost looks like welding flash) bits stuck to the magnet. But the tank itself looks spotless, no signs of any severe rust or metal contamination aside from the stuff on the magnet. The desired FRP pressure pid at idle shows 65psi, the actual PID never goes over 50-51psi, which leads me to believe the pump is starting to crap out. There are no driveability issues at this time aside from the CEL being on. I have checked the fuel filter and found no restriction issues at all there.. I'd like to stick a manual gauge on this thing, but I'd have to "make it work" as these vehicles don't have any provisions for a mechanical fuel pressure gauge to be installed. Also, I'm not sure that I'd even have a good reference point because, as far as I know, the FRPS is referenced to manifold vacuum and not atmospheric pressure, and so I don't know how heavily that will affect the mechanical gauge reading VS the PID's pressure reading. We don't have a fuel injector cleaning kit here and so I can't find another way to manually pressurize the fuel rail and monitor PID data to isolate a bad sensor... I've never seen FPRS failure do this before, usually the pid just skyrockets when the sensor fails and the car runs like complete garbage, if at all, and I'm really leaning toward the pump at this point. But I don't want to be wrong here, it's a valuable account to our shop and they don't really give "2nd chances" so I need to be sure that the part I quote will fix this. Any opinions or advice would be much appreciated! Dave Quote Link to comment Share on other sites More sharing options...
mchan68 Posted January 25, 2010 Share Posted January 25, 2010 I realize this isn't the proper tool for the specific application you are working with, but perhaps the tool is this graphic might help: Quote Link to comment Share on other sites More sharing options...
DamageINC Posted January 25, 2010 Author Share Posted January 25, 2010 Yeah, I found a kit here that might let me tap into the feed line and "tee" my gauge into a reading. Truth be told, it just seems like a weak pump, which was my initial hunch 9 seconds into this job, lol. FRP drops down to 28 psi under WOT and around 40-something while cruising, spec is 65 psi. It can generate pressure KOEO but it just seems to lack volume. I'm trying to find duty cycle specs/references just to see if the pump is being commanded more heavily than "normal" to compensate for the lack of pressure. Even at idle, it hovers around 50psi and it's looking for 65, the duty cycle is at 49%. Dave Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted January 25, 2010 Share Posted January 25, 2010 IIRC, and DON'T QUOTE me on this, the scan pid is doubled for actual FP command. This means FPDC at 49% means the pump command is at 98%, which is way too high (possibly indicating a bad FP). Also, fuel pressure (FRP PID) indicated in scan data will be 7-10PSI measured with a guage . From my notes: Vacuum Hose Connected Gauge fuel pressure – 30 psi FRP PID – 39 psi Vacuum Hose Disconnected Gauge fuel pressure – 52 psi FRP PID – 59 psi FP Duty Cycle Command / PCM Status /Fuel Pump Driver Module Actions Less than 5%/ Fault /The FPDM will send a 25% duty cycle to the PCM. The fuel pump will be off. 5-50% / Normal operation /FPDM will operate the fuel pump at the speed requested. FP duty cycle X 2 = Pump speed % of full on. The FPDM will send 50% duty cycle to the PCM. 51-68% / Fault /The FPDM will send a 25% duty cycle to the PCM. The fuel pump will be off. 75% /Fuel Pump Off /The FPDM will not operate the fuel pump. The FPDM will send a 50% duty cycle to the PCM. Over 76% / Fault /The FPDM will send a 25% duty cycle to the PCM. The fuel pump will be off. The Fuel Pump (FP) signal is a duty cycle command sent from the powertrain control module (PCM) to the fuel pump driver module (FPDM). The FPDM uses the FP command to operate the fuel pump at the speed requested by the PCM or to turn the pump off. Example: FP duty cycle = 40%. 40 X 2=80. Pump is run at 80% of full on Note: For the Thunderbird and Lincoln LS models, the FPDM functions are incorporated in the Rear Electronic Module (REM). Fuel pump operation is the same as applications using the stand-alone FPDM. The REM will, however, communicate diagnostic information through the BUS +/- circuits (SCP) instead of using a fuel pump monitor (FPM) circuit. To access the data you will need a scan tool that can communicate with the REM. 50% duty cycle = 100% pump command 25% duty cycle = 50% pump command Since most outputs on a vehicle are activated by grounding the circuit, duty cycle is usually measured as the percentage of time that the voltage signal is low. In the case of the FPDM, the FP data PID displays the duty cycle that the voltage is high. PID Duty Cycle = 25% Scope Displays 75% During a key up, the PCM initially commands a 50% duty cycle high and then it quickly drops to about a 25% duty cycle high. Make sure to reset KAM when done! Good Luck! Quote Link to comment Share on other sites More sharing options...
mrbudge Posted January 25, 2010 Share Posted January 25, 2010 If fuel pressure drops on accell, and the filter is ok, you will need a pump. Just make sure that you have no voltage drop at the fuel pump driver module, check it under load. Quote Link to comment Share on other sites More sharing options...
Adam_Dodson Posted January 26, 2010 Share Posted January 26, 2010 up here we do these pumps like tire rotations...test drive and monitor FRP at WOT. you will see it drop off usually to about 5psi. If you have no FPDM DTCs its pretty much a guaranteed pump and filter change. Quote Link to comment Share on other sites More sharing options...
DamageINC Posted January 26, 2010 Author Share Posted January 26, 2010 Yeah, it was just the pump. I just wanted to be absolutely 100% positive before doing it because this fleet is absolutely unforgiving if there's any misdiagnosis, so being 99% sure still doesn't make me feel better with them, haha. But the difference was instant, I put the new pump in and FRP jumped to 65psi IMMEDIATELY at startup and FP duty cycle (demand) dropped to about 18% at idle, so far so good. They understand that there's still a potential for further contamination without tank replacement but personally I don't believe there will be an issue. Thanks to everyone for the input though! Dave Quote Link to comment Share on other sites More sharing options...
Tony302600 Posted February 1, 2010 Share Posted February 1, 2010 been there done that...fuel pump...did the tests with duty cycle PID which helped out ALOT Quote Link to comment Share on other sites More sharing options...
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