Code P0191

[RamVenture]

I've post here before about my P0191 (Fuel Rail Pressure Sensor - range/performance problem). I had this code going on 3yrs. Truck is 2012 2500 stock with 155k miles. I've replaced the FRP senor, the FCA senor, and multiple genos OEM fuel filters. From a performance perspective I haven't notice any issues, so I've just lived with it. I'm planning a couple longer camping trips with the family and would like to get this issue finally resolved without spending too much money on needless parts. Using the Car Sanner Pro app I'm able to monitor both command and supply fuel rain pressure and supply is usually about 200psi under command this works out to about 2% under command which IMO is reasonable although I have no data to compare. What I have noticed is the MIL comes on when driving around time. Once we hit the freeway for a trip the MIL will clear next day. When I'm at the stop light the truck will sometimes idle a little funny and fuel pressure can drop as low as 4,400psi. I have started to suspect it’s likely a leaky injector’s. I had an oil analysis done some time back and no fuel in the oil was detected.

Looking through some closed threads on this topic I came across this interesting diagnostic. I think the funny idling is the truck running this diagnostic test. The truck doesn’t always idle funny, but when it does I know the MIL is coming soon and that’s when happened today.

Looking for suggestions on steps on how I should go about having the injectors test. I’ve read the injector tubes can leak. Is this something that can be fixed by checking torque? I’ve also read there is a flow test that can be run without removing the injectors. I’m not sure if this is something a normal diesel shop can perform or if this would need to be done at a RAM dealership? Thank you for your time and input!

 

[sag2]

If you are handy, retorquing the connector tubes is free and should take a couple hours. You can check the return flow of the injectors yourself (might be wise to do in conjunction with connector tube torque) if you have a Miller 9012 and 9864 or equivalent special tool and a good graduated cylinder or container. You can use Alfa OBD to perform the fuel pressure override test, otherwise disconnect the FCA, the result will be pretty close to using the ECM to up the pressure.


INJECTOR RETURN FLOW TEST
#ad
Special Tools: Click to display a list of tools used in this procedure

Click here to launch the form to order any tools you need.

9012 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9014 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9864 - Cap, Fuel Rail

Originally Shipped In Kit Number(s) 9860.
9011 - Adapter, Fuel Pressure Test

Originally Shipped In Kit Number(s) 8848, 8849, 8849CC.

2

No
[/paste:font]

• 3

9012 in place of the banjo connector. NOTE: Do not use test fitting 9014 . This fitting will block return flow from the High Pressure Delivery Pump and damage the seal and could potentially damage the engine.
5. Install a 5/16 diameter rubber fuel hose (Hose A) onto the test fitting and into a fuel container. NOTE: This hose is used to measure the High Pressure Pump return flow.
6. Remove the vehicle fuel return line (Quick connect) from the engine fuel drain tube.
7. Install a 5/16 diameter rubber fuel hose (Hose B) onto the engine fuel drain tube and into the fuel container. NOTE: This hose will be used to measure the Injector return flow for this procedure.
8. Start engine and allow to idle for 30 seconds. This step allows the flows to stabilize.
9. Using the scan tool, navigate to ECM view -> PCM Cummins -> More Options-> System Tests -> Fuel Pressure Override Test. Select Start, then press Next. NOTE: While the test is running, record the FCA duty cycle % and actual rail pressure.
10. Press the Run button to start the Fuel Pressure Override Test. The engine speed will elevate rapidly to 1200 RPM and the rail pressure will increase to 26107 psi (1800 bar). At this point, move (Hose B) from the bucket and insert it into a graduated cylinder. Collect the fuel until the Fuel Pressure Override Test times out (30 seconds).
11. Measure and record the amount of fuel collected in the graduated cylinder. Repeat this three times and take the average of the three results. NOTE: Flow should be less than 210 ml for 30 seconds.
12. If the flow is less than 210 ml/30 seconds, the test has successfully passed. If the flow is greater than 210 ml/30 seconds, turn off the engine and remove all 6 high pressure fuel lines. Re-torque the high-pressure connector nut for each injector. Inspect for damage, repair/replace as necessary. Reinstall the high pressure fuel lines. Re-measure the injector return flow using steps 10 through 13 as a guide. Continue on to next step.
13. If the amount of fuel is still greater than 210 ml/30 seconds after re-torquing the high-pressure connector nuts, turn the engine off and remove the #1 high pressure fuel line. Cap the #1 fuel port using tool 9864 for the 6.7L engine on the fuel rail and re-measure the injector return flow using steps 8 through 11 as a guide. Repeat this procedure for injectors 2-6. Continue on to next step.
14. Replace the Fuel Injector and High pressure connector of the injector that shows the largest amount of change when capped off.


Did the vehicle pass the Injector Return Flow test at step 12 without any repairs needed

Yes
[paste:font size="3"]

• (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure) .

 

[Signal73]

Just one experience, but I solved a 191 code by replacing the rail pressure relief valve. For sure do the diagnostics first though.

 

[RamVenture]

Unfortunately, I think this is beyond my mechanical ability without a good guide. Do you know if there are any good YouTube videos showing this process? I’ve learned a lot watching the Motor City Mechanic and his great videos. Has given me confidence to take on some jobs.

If you are handy, retorquing the connector tubes is free and should take a couple hours. You can check the return flow of the injectors yourself (might be wise to do in conjunction with connector tube torque) if you have a Miller 9012 and 9864 or equivalent special tool and a good graduated cylinder or container. You can use Alfa OBD to perform the fuel pressure override test, otherwise disconnect the FCA, the result will be pretty close to using the ECM to up the pressure.


INJECTOR RETURN FLOW TEST
#ad
Special Tools: Click to display a list of tools used in this procedure

Click here to launch the form to order any tools you need.

9012 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9014 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9864 - Cap, Fuel Rail

Originally Shipped In Kit Number(s) 9860.
9011 - Adapter, Fuel Pressure Test

Originally Shipped In Kit Number(s) 8848, 8849, 8849CC.

2

No
[/paste:font]

• 
  
  
  • 3

9012 in place of the banjo connector. NOTE: Do not use test fitting 9014 . This fitting will block return flow from the High Pressure Delivery Pump and damage the seal and could potentially damage the engine.
5. Install a 5/16 diameter rubber fuel hose (Hose A) onto the test fitting and into a fuel container. NOTE: This hose is used to measure the High Pressure Pump return flow.
6. Remove the vehicle fuel return line (Quick connect) from the engine fuel drain tube.
7. Install a 5/16 diameter rubber fuel hose (Hose B) onto the engine fuel drain tube and into the fuel container. NOTE: This hose will be used to measure the Injector return flow for this procedure.
8. Start engine and allow to idle for 30 seconds. This step allows the flows to stabilize.
9. Using the scan tool, navigate to ECM view -> PCM Cummins -> More Options-> System Tests -> Fuel Pressure Override Test. Select Start, then press Next. NOTE: While the test is running, record the FCA duty cycle % and actual rail pressure.
10. Press the Run button to start the Fuel Pressure Override Test. The engine speed will elevate rapidly to 1200 RPM and the rail pressure will increase to 26107 psi (1800 bar). At this point, move (Hose B) from the bucket and insert it into a graduated cylinder. Collect the fuel until the Fuel Pressure Override Test times out (30 seconds).
11. Measure and record the amount of fuel collected in the graduated cylinder. Repeat this three times and take the average of the three results. NOTE: Flow should be less than 210 ml for 30 seconds.
12. If the flow is less than 210 ml/30 seconds, the test has successfully passed. If the flow is greater than 210 ml/30 seconds, turn off the engine and remove all 6 high pressure fuel lines. Re-torque the high-pressure connector nut for each injector. Inspect for damage, repair/replace as necessary. Reinstall the high pressure fuel lines. Re-measure the injector return flow using steps 10 through 13 as a guide. Continue on to next step.
13. If the amount of fuel is still greater than 210 ml/30 seconds after re-torquing the high-pressure connector nuts, turn the engine off and remove the #1 high pressure fuel line. Cap the #1 fuel port using tool 9864 for the 6.7L engine on the fuel rail and re-measure the injector return flow using steps 8 through 11 as a guide. Repeat this procedure for injectors 2-6. Continue on to next step.
14. Replace the Fuel Injector and High pressure connector of the injector that shows the largest amount of change when capped off.


Did the vehicle pass the Injector Return Flow test at step 12 without any repairs needed

Yes
[paste:font size="3"]

• (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure) .

If you are handy, retorquing the connector tubes is free and should take a couple hours. You can check the return flow of the injectors yourself (might be wise to do in conjunction with connector tube torque) if you have a Miller 9012 and 9864 or equivalent special tool and a good graduated cylinder or container. You can use Alfa OBD to perform the fuel pressure override test, otherwise disconnect the FCA, the result will be pretty close to using the ECM to up the pressure.


INJECTOR RETURN FLOW TEST
#ad
Special Tools: Click to display a list of tools used in this procedure

Click here to launch the form to order any tools you need.

9012 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9014 - Fitting, Fuel System Test

Originally Shipped In Kit Number(s) 8999, 8999CC.
9864 - Cap, Fuel Rail

Originally Shipped In Kit Number(s) 9860.
9011 - Adapter, Fuel Pressure Test

Originally Shipped In Kit Number(s) 8848, 8849, 8849CC.

2

No
[/paste:font]

• 
  
  
  • 3

9012 in place of the banjo connector. NOTE: Do not use test fitting 9014 . This fitting will block return flow from the High Pressure Delivery Pump and damage the seal and could potentially damage the engine.
5. Install a 5/16 diameter rubber fuel hose (Hose A) onto the test fitting and into a fuel container. NOTE: This hose is used to measure the High Pressure Pump return flow.
6. Remove the vehicle fuel return line (Quick connect) from the engine fuel drain tube.
7. Install a 5/16 diameter rubber fuel hose (Hose B) onto the engine fuel drain tube and into the fuel container. NOTE: This hose will be used to measure the Injector return flow for this procedure.
8. Start engine and allow to idle for 30 seconds. This step allows the flows to stabilize.
9. Using the scan tool, navigate to ECM view -> PCM Cummins -> More Options-> System Tests -> Fuel Pressure Override Test. Select Start, then press Next. NOTE: While the test is running, record the FCA duty cycle % and actual rail pressure.
10. Press the Run button to start the Fuel Pressure Override Test. The engine speed will elevate rapidly to 1200 RPM and the rail pressure will increase to 26107 psi (1800 bar). At this point, move (Hose B) from the bucket and insert it into a graduated cylinder. Collect the fuel until the Fuel Pressure Override Test times out (30 seconds).
11. Measure and record the amount of fuel collected in the graduated cylinder. Repeat this three times and take the average of the three results. NOTE: Flow should be less than 210 ml for 30 seconds.
12. If the flow is less than 210 ml/30 seconds, the test has successfully passed. If the flow is greater than 210 ml/30 seconds, turn off the engine and remove all 6 high pressure fuel lines. Re-torque the high-pressure connector nut for each injector. Inspect for damage, repair/replace as necessary. Reinstall the high pressure fuel lines. Re-measure the injector return flow using steps 10 through 13 as a guide. Continue on to next step.
13. If the amount of fuel is still greater than 210 ml/30 seconds after re-torquing the high-pressure connector nuts, turn the engine off and remove the #1 high pressure fuel line. Cap the #1 fuel port using tool 9864 for the 6.7L engine on the fuel rail and re-measure the injector return flow using steps 8 through 11 as a guide. Repeat this procedure for injectors 2-6. Continue on to next step.
14. Replace the Fuel Injector and High pressure connector of the injector that shows the largest amount of change when capped off.


Did the vehicle pass the Injector Return Flow test at step 12 without any repairs needed

Yes
[paste:font size="3"]

• (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure) .

 

[RamVenture]

Just one experience, but I solved a 191 code by replacing the rail pressure relief valve. For sure do the diagnostics first though.

What symptoms was your truck experiencing? From other post I read of people losing power when the relief valve opens. Since I never lost any power, I figured it’s fine.

 

[Topzide]

After searching other threads on this code, and knowing how the systems work in these trucks, I would look for wiring and or connectors. These trucks work on their own type of intranet. This means that it has an network in the truck to talk with the modules. This system runs on 5 volts. Stop the parts cannon and get a factory repair manual for the truck and follow the steps for the issue. I got the factory manual for my truck right after I acquired it. It has help me in the maintenance along with repair issues. A good scanner for the truck is a must. Not sure how much AlfaOBD covers you year truck, but might be worth the investment. It's available for Android and Windows, no iOS support. Keeping providing info for others to be able to help you with the issue. Just seems strange that it's been going on this long without the truck being down.

 

[Signal73]

What symptoms was your truck experiencing? From other post I read of people losing power when the relief valve opens. Since I never lost any power, I figured it’s fine.

Nothing other than an illuminated CEL.

 

[RamVenture]

Nothing other than an illuminated CEL.

Thanks for the information. I suspected there would be more noticeable issues if the FRV was leaking. I’m taking the truck into a shop next week that will be checking for electrical issues. Testing electrical issues is not my strong suit. I will mention testing the FRV. Is there a simple discount location for the PRV to see if there is fuel leaking by? I’m not sure where is drains back, fuel tank or fuel filter canister. Does the downstream side have fuel pressure? If it’s not to difficult I might take on this inspection.