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Posted

2016 1500 6.2l. Having a intermittent rough idle stumble and even stumbles with increase to 1000k RPM. Its slight but noticeable. I have a cheap OBD2 bluetooth and Torque app for reading. I don't know how accurate it is, but figure all its doing is sending numbers, so should be find. With my truck idling fuel pressure is sporadic around 45psi with dips to 30 and even 22 psi, then sometimes up to 50psi. This seemed to be at about the same frequency as my stumble. The other reading if Fuel rail pressure which is much higher and cycles high and low but not as drastically. Is this normal? I tried attaching a screen shot. The numbers on the left are wrong but the graph shows the fluctuation. If someone knows the right reading to be expected or have a sensor to check their truck and see what the reading are, I would appreciate it.

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Posted

Being so heavily computer controlled, I'd be willing to bet that it is normal. Mind you to, some of these handheld OBD devices and what not don't always have near the reading capabilities of the GM MDI and GDS2 system can show. If it were low enough or long enough, it would be setting low fuel pressure codes left and right.

 

 

Electronic Returnless Fuel System

The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rail. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. The pressure relief regulator valve within the fuel tank provides an added measure of over pressure protection. Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the fuel pump driver control module via a GMLAN serial data message. A fuel pressure sensor located on the fuel feed pipe provides the feedback the engine control module requires for Closed Loop fuel pressure control.

Fuel Pump Driver Control Module

The fuel pump driver control module is a serviceable GMLAN module. The fuel pump driver control module receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The fuel pump driver control module sends a 25 kHz PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 22 A.

Fuel Pressure Sensor

The fuel pressure sensor is a serviceable 5 V, 3-pin device. It is located on the fuel feed line forward of the fuel tank, and receives power and ground from the engine control module through a vehicle wiring harness. The sensor provides a fuel pressure signal to the engine control module, which is used to provide Closed Loop fuel pressure control.

 

 

Posted

Yeah i figure it would through codes if bad enough. I have had misfire code previously chalked up to faulty spark plug. Dont know if that was just BS. I figure these things have certain parameters that dont throw codes as long as its able to adjust. Just like it wont throw a misfire code unless its really bad multiple misfires. My question is that if its normal or is the system having to constantly adjust/compensate to stay just below the code throwing threshold?

  • 5 years later...
Posted

Can someone please help me I’m trying to replace the flex fuel composition sensor I pulled the fuel pump fuse and relay but I’m still holding pressure… please help me I have nothing but problems with this truck

 

  • 1 year later...
Posted

Did you ever get this figured out? My 2017 GMC Yukon is behaving almost identically and not normal in my experience. Any help would be appreciated. 

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    • That makes sense, and I think you are describing the real product problem. Capturing data is the easy part. If the owner or technician has to manually dig through five minutes of millisecond-level logs, the product has already failed. The device would be at the ECM harness, not at the OBD port, so I agree that data retrieval and event marking need to be thought through carefully. The way I am thinking about the architecture is: The recorder itself should not depend on a phone, app, Bluetooth, Wi-Fi, or cloud connection to capture the event. It should always keep a local rolling buffer and lock the event locally. A button, phone app, or small cabin device would only act as an event marker. If the driver feels a stumble and presses the button 10–30 seconds later, the pre-buffer has to already contain the useful data. For data retrieval, the practical options would be a sealed service USB lead, Wi-Fi download, or a phone/cabin companion device. I would not expect the owner to remove the ECM-side module or work with raw files directly. The cloud or AI side would be for interpretation, not for capturing the event. The truck may have no connection when the issue happens, so the evidence has to be saved locally first. After that, cloud processing could help decode the data, compare it against baselines, and generate a readable report. For the first version, I would keep the automatic triggers conservative and objective: driver event marker bus-off error passive voltage drop / brownout device reset FIFO or queue overflow a normally periodic message disappearing side-to-side communication mismatch, if the topology supports that For “learning normal,” I agree with your point, but I would not want to overclaim it as automatic root-cause diagnosis at first. A realistic first step would be learned baseline comparison for that specific vehicle and operating condition. For example, a value would only be compared against similar conditions: RPM range load / MAP throttle position gear / vehicle speed coolant and oil temperature battery voltage AFM/DFM state, if decoded and validated Then the report could flag things like: this periodic message disappeared compared with its normal timing this value deviated from this vehicle’s normal range under similar conditions the same abnormal pattern repeated after the same type of event the anomaly occurred together with voltage, oil-pressure, misfire, or communication changes But I would still call that “abnormal pattern detected,” not “replace this part,” unless there is enough validated repair data behind it. So the intended product would not be “here is a huge log.” It would need to be an event package: what triggered the capture how much pre/post data was preserved what changed before and after the event whether the device itself reset, overflowed, or saw a bus error selected graphs around the event raw data only as supporting evidence From your perspective, what would make this kind of report useful instead of just another datalog? For example: What are the top 5 parameters or events you would want highlighted first? Would you trust a learned baseline for that specific vehicle, or would you prefer fixed thresholds? How much false-positive flagging would be acceptable before you stopped looking at the reports? What would a one-page report need to show for an independent shop to take it seriously? For misfire, AFM/DFM, oil pressure, or U-code complaints, what would you want the tool to flag automatically?
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