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| CRD Fuel Rail Pressure Question http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=86461 |
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| Author: | Phatjimmy [ Wed Apr 19, 2017 2:45 pm ] |
| Post subject: | CRD Fuel Rail Pressure Question |
Hello LOST brothers, I have been lurking on this forum for years now and you guys have helped me be comfortable with my CRD and our love/hate relationship. I am pleased to say that I have a little over 190K miles now on my CRD with no major failures (knock on wood). But that being said, I am posting here because I am starting to have things wear out now. So here is my issue I have been dealing with. I was having a hot start issue. I could go on a hour drive without issue. Shut the beast off for about 30 min and upon restart is would barely run. The only code it would kick was for multipal cylinder misfire (P0300). My scanner would not show rail pressure. I would let it sit until the next day and she would start up and run fine. No codes, no nothing. So talking with my coworkers who all own common rail cummins powered trucks, they said it sounded like a FCA (MPROP) was getting stuck. So I replaced it. Now the beast runs better then ever and is very peppy. So a good fix I think. I was able to borrow a scan tool from another coworker that reads rail pressure yesterday. So I looked and my reading is all over the place. The ECM is reporting ranges from 800 psi to 98,243 psi. But it fluctuates rather fast and constantly. So needless to say I am kind of lost on how to troubleshoot this. These fuel rail items are not cheap and I hate throwing parts at something so I need all your collective brains to help me on this one. I figured if this reading is so unstable this may be what was overheating my MPROP and causing it to stick?? So here is what I have done today. If I unplug the rail pressure sensor (5159963AA) with engine on, the engine runs smoother but I get a CEL for rail pressure fail High. The reading on the scanner freezes at 2235 psi. With the sensor plugged in and engine off I get a varying reading of two numbers, 24037.0 psi and 15901.4 psi in random order always. When I crank the engine, it briefly goes to 5442.0 psi and then starts the all over the map readings. So Is this the pressure sensor it's self or something else? |
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| Author: | flash7210 [ Wed Apr 19, 2017 3:23 pm ] |
| Post subject: | Re: CRD Fuel Rail Pressure Question |
First: I would say that the scan tool is not communicating properly with the ECM. CP3 max pressure is 30,000 psi. So that 98k number is right out. Second: With the engine running at idle, grab the wires at the rail pressure sensor and wiggle them. If the engine sputters and stumbles then you need to replace the harness connector. Do the same with the wires at the MPROP. If it sputters and stumbles, replace that connector too. The most cost effective and reliable diagnostic tool is a Android phone/tablet with TorquePro app using a ELM327 OBD bluetooth adapter. A AutoMeter fuel rail pressure gauge can also be helpful sometimes. I use both. |
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| Author: | mass-hole [ Fri Apr 28, 2017 2:02 am ] |
| Post subject: | CRD Fuel Rail Pressure Question |
The rail sensor only reads up to 1800 bar or ~26107 psi So you should never see more than that from the Ecu. Pressure should be 0 or near zero with the engine off. No more than 14.7 psi I don't think. The failing high when the sensor is unplugged is a failsafe I believe. The Ecu internally maxes out the pressure when it senses that the sensor was unplugged to prevent over pressurization. Basically it tells itself it's at 1800 bar so that the solenoid dumps the pressure. Sent from my iPhone using Tapatalk |
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| Author: | GordnadoCRD [ Fri Apr 28, 2017 3:00 am ] |
| Post subject: | Re: CRD Fuel Rail Pressure Question |
I wouldn't second guess the need for MPROP replacement, as you've already seen the results. Secondly, the MPROP is "upstream" of all high pressure fuel, so any shenanigans there cannot influence the MPROP directly. The only way would be if the ECM also sees the readings that you are and believes them. It would be trying to correct them within the limits of it's capability. I doubt that it is though, as if it believes those readings, it would shut everything down to protect the whole injection system. Some of your readings are impossible, so I would look for poor connections, or wires with failed insulation Or, as Flash mentioned tool interface with the vehicle. Also check to make sure the scantool you use (now or future) is configured to be compatible with your Jeep. Rail pressure readings are not all the same. Dodge Cummins uses a different fuel pressure sensor than the Jeep. Weirdly, the GM DMax uses the same one as the CRD Jeep. |
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| Author: | mass-hole [ Fri Apr 28, 2017 3:53 pm ] |
| Post subject: | Re: CRD Fuel Rail Pressure Question |
GordnadoCRD wrote: I wouldn't second guess the need for MPROP replacement, as you've already seen the results. Secondly, the MPROP is "upstream" of all high pressure fuel, so any shenanigans there cannot influence the MPROP directly. The only way would be if the ECM also sees the readings that you are and believes them. It would be trying to correct them within the limits of it's capability. I doubt that it is though, as if it believes those readings, it would shut everything down to protect the whole injection system. Some of your readings are impossible, so I would look for poor connections, or wires with failed insulation Or, as Flash mentioned tool interface with the vehicle. Also check to make sure the scantool you use (now or future) is configured to be compatible with your Jeep. Rail pressure readings are not all the same. Dodge Cummins uses a different fuel pressure sensor than the Jeep. Weirdly, the GM DMax uses the same one as the CRD Jeep. I think some of the Cummins may have a compatible sensor as well: http://www.glowshiftdirect.com/white-maxtow-30-000-psi-fuel-rail-pressure-gauge.aspx That gauge works with the Cummins and Dmax and plugs in directly inline with the rail pressure sensor wiring. Make sure when you are reading from the OBD port that whatever device you are using is set to the ISO 9141-2 protocol |
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| Author: | Phatjimmy [ Mon May 01, 2017 11:07 am ] |
| Post subject: | Re: CRD Fuel Rail Pressure Question |
Thanks for the replies. I have checked all connections and everything seems tight and no engine changes when wiggling connectors. I think the scan tool I was using was just junk. I like Flashes suggestions as well. I will invest in Torquepro. But still overall the little beast runs far better then it has in a long time. So I corrected an issue regardless with the MPROP change. Thanks a bunch guys! |
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| Author: | mass-hole [ Tue May 02, 2017 12:53 pm ] |
| Post subject: | Re: CRD Fuel Rail Pressure Question |
Phatjimmy wrote: Thanks for the replies. I have checked all connections and everything seems tight and no engine changes when wiggling connectors. I think the scan tool I was using was just junk. I like Flashes suggestions as well. I will invest in Torquepro. But still overall the little beast runs far better then it has in a long time. So I corrected an issue regardless with the MPROP change. Thanks a bunch guys! Torque Pro is nice. You do need android. Sent from my iPhone using Tapatalk |
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