Twice now after starting my truck the engine immediately stumbles (RPM drops to 600 or so for a brief moment), trips the CEL then returns to normal idle. Pulling the code I get P0191 which I believe is fuel pressure related. Does anyone have any idea what may be causing this? It has done it twice now, once a week before Christmas and a second time today. The first time the code cleared itself after about 5 days. Thanks for the help...

 

Here is what I found on the code.....

WHEN MONITORED
At key on.

SET CONDITION
The fuel pressure sensor reading at key on does not match the expected fuel pressure reading at key on.

POSSIBLE CAUSES

• Other DTC's present
• Fuel rail pressure sensor
• Fuel system tampering
• Intermittent condition

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding

DIAGNOSTIC TEST

1.OTHER DTC'S PRESENT</B>
With the scan tool, read DTCs.
Q: Are any DTC's present?

YES: Repair other DTC's first. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
NO: Go To 2


2.FUEL PRESSURE READING</B>
Using the scan tool, monitor the actual fuel pressure reading while the key is on and engine is not running.
Q: Is the actual fuel pressure reading greater than 870 psi?

YES: Go To 3
NO: Refer to the INTERMITTENT CONDITION Symptom (Diagnostic Procedure).
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).


3.FUEL RAIL PRESSURE SENSOR</B>
Visually inspect the fuel system components for signs of tampering, pay particular attention to the fuel pressure sensor on the and the fuel pressure sensor wiring harness.
Q: Were any signs of tampering discovered?

NO: Replace the Fuel rail pressure sensor. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
YES: Restore Fuel system to original condition. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).


hope this helps some

53
Mark

 

Put some dielectric grease on the MAP and Rail Pressure Sensor connectors. Seems to fix the issue with the Quad boxes.

MikeyB

 

Pulling the code I get P0191 which I believe is fuel pressure related. Does anyone have any idea what may be causing this?


Quadzilla and Xzillaraider causing unexpected pressure to the sensor?

 

Probably caused by a intermittent connection on the rail sensor. I had a similar issue (P0191) with the Edge EZ rail sensor connector. A little adjustment on the pins and some dielectric grease fixed the issue.

MikeyB

 

Dielectric grease = Yes

 

53 ******, thanks for the post...that's good info to know.

Well, I started the truck up this morning and the CEL was out. I guess I'll go over the connectors and see what I find. I also need to install the fuel pressure option of the Commander. I have all the parts just haven't go around to doing it. That may tell me something.

 

No problem!

the 3rd cause makes me laugh...

POSSIBLE CAUSES

• Other DTC's present
• Fuel rail pressure sensor
• Fuel system tampering
• Intermittent condition

Have you been tampering with your fuel system??


This seems like one of the codes that if the dealer reads, they might start to question if you have a box/programmer on your truck.


anyway let us know what you find.

 

I had this code right after I purchased my truck last year, think it was in April. No box or programmer on the truck, bone stock at that time. They have a TSB that is related, something to do with KEY ON, or better stated KEY ON too long before STARTUP. Seems when you turn the key on the computer expects to see you start the engine in a certain amount of time. When this does not happen in a timely manner, you throw the code. It is also programmed to see startup shortly after the 'grid heater coil' light goes out. The TSB effectively sets a new time value, or timeframe value to the difference between key on and startup.

If you have your Quad box in the OFF position at startup, it would not be affecting anything UNLESS there IS an issue at the plugs - ie:contacts. You should have used a little dielectric grease at the time you installed your box.

If the rail pressure suddenly drops it will throw the code. If the relief valve sticks after opening, and does not close properly it will throw the code. If the CP3 is not putting enough volume into the rail it will throw the code. A dirty fuel filter will cause the code. Lots of possibilities to choose. The drop in RPM and the studdering suggest the fuel pressure was intermittent in the rail -defuel or less than expected by the variable sensing at the rail. The return to correct RPM afterwards makes me think that the relief valve may possibly be involved.
when I had the problem with this code my dealership replaced my relief valve, no problem since. The tech told me that these valves were running 50/50, some good, some bad at that time.

CD

 

I've just got a six hundred miles on my truck and the check engine light is now on. The code is P0191. I've read about the cause sometimes being delays in starting etc, but no more times than its been started I'm sure the start followed imediately after the warm-up light went off. I guess it's back to the dealer which is 60 miles.
Thanks for any help.

 

I should have posted tis earlier. My problem turned out to be a broken connector on the fuel pressure sensor. So bwyckoff, check your connections.

 

Thanks PTGARCIA. I'll try that as soon as I get the 4 inches of solid ice off the truck and can open the hood.
bwyckoff