Datalog shows LPFP sensor pinned at 55.7 psi

[e1]

I just picked up a 100k miles 2008 135i with DPs and an MHD Stage 2 tune no other relevant mods to this post other than 1-step colder NGK Laser Iridium spark plugs. I just reflashed the tune with my own license to MHD Stage 2 to remove the burble tune and map linear throttle (was previously mapped to Stage 2 upon purchase).

Anyway as the title states I am seeing my Fuel Low Pressure Sensor PSI stuck pinned at 55.7 psi at all times. Doesn't matter if it's on or off throttle, or at WOT. I have some logs that show very very minor blips but basically just a flat line. Here are two logs, one from before the spark pugs and the other from after.

Before: https://datazap.me/u/e1/3rd-gear-pull-8-11-20
After: https://datazap.me/u/e1/log-1597531343

I don't have any error codes but I'm not sure if the sensor that sends this data is bad or if the fuel pump is suspect, and I'm a little nervous if the pressure is actually this low as it's nearing to low limit threshold for safe fueling. Oh, another thing is that 2 injectors seem to be leaking, not sure if that info adds anything or not. Any info would be greatly appreciated.

Thanks for looking.

[drwillb]

There is no LPFP sensor on our cars. That’s why you’re not getting output on that data channel.

[e1]

Originally Posted by drwillb

There is no LPFP sensor on our cars. That’s why you’re not getting output on that data channel.

I understand it's not the actual LPFP sensor but from what I understand it's a sensor on the low pressure portion of the fuel system. I have seen other n54 data logs with values ranging from 50-75psi and fluctuating during normal operation.

[e1]

I double checked and I was incorrect in saying there were no codes. What I should have said was no stored DME codes but I do have 2AAF - DME: Fuel pump, plausibility as a shadow code. I'm wondering if maybe the sensor just needs to be replaced.

[e1]

Found info that shows these sensors fail and display 55.7 psi at all times. Got a new one and looking forward to seeing if the 2AAF code goes away or stays there. Stock fuel pump might not be up for the job of MHD 2.

[SixBanger]

Please follow up if that worked out for you

[smi2710]

i consistently get a 2AAf code and being on map 2 of my jb4 i max out the LPFP. From everyone i have spoke with they suggest a stage 2 LPFP fro map 2 and above

[Petro135]

I was getting 2aaf code when changed to mhd stg2+ and changed to a homemade bucketless stg2 pump and it stopped causing a code to pop up but when I scan for other things the 2aaf is still a shadow code. But is not an issue anymore. Dont know if that helps you at all

[e1]

Originally Posted by SixBanger

Please follow up if that worked out for you

I installed the new sensor and now get real values for Low Pressure Fuel Pump. It looks like my pump is either getting a little tired, not able to flow enough fuel for MHD Stage 2, or a little of both. I have gotten lowest readings of about 54 psi in the higher RPMs under WOT but only very briefly. But after some driving the 2AAF code came back under shadow codes, so it's the same as before in that case.

Likely going to do the Walbro 450 PnP pump next, but I also noticed wonky CPS readings after doing the install and need to double check I didn't damage any wiring for that while I was in there.

[c0bra]

Sounds like your LPFP is working just fine. If you plan on running aggressive E85 mix or custom tune, then go ahead and upgrade the pump.

I've got 33k miles on my N54. LPFP runs steady around 70-72 psi at idle and dips down to low 50s (usually 54-55 psi) very briefly at WOT. My logs from MHD Stg 1, 1+, and 2+ all look similar in that regard. Also have the 2AAF plausibility shadow code, and from what I read that's common.

Google "How to read MHD data logs" and you'll find a good document you can reference. LPFP info from there says...

<50PSI sustained LPFP (Low Pressure Fuel Pump) is not acceptable - The occasional dip below 50PSI is not usually a cause for concern, it’s a sustained pressure below 50PSI that is typically indicative of a failing LPFP or perhaps a high ethanol content fuel coupled with an aggressive tune, in either case the LPFP should be addressed.

[ShocknAwe]

2aaf is meaningless for most people. Ignore it.

If LPFP reading is pinned, bad sensor.

If LPFP dips, it's the pump, line, venturi, etc.

If car randomly dies, and LPFP is inconsistent, it's likely EKP.



FYI, my LPFP threshold is 60psi. 50-60 and the HPFP supply starts to become more inconsistent which can cause you to run lean. This is on modified cars of course. <50 is more of a stop driving the car and fix it asap kind of scenario.

Cheers guys.

[e1]

Thanks guys. I have seen the how to read MHD logs in the past and was referencing that. I can post another log showing my actual HPFP and LPFP data. It seems like the HPFP falls off very rapidly though only ever getting down to ~1500 psi.

But I need to address my ignition timing issue now, I am getting sudden drops to zero abruptly. I'm thinking it might be sensor/wiring related since I was yanking on the harness to make room for the fuel sensor tube assembly I installed. But that is for a different thread if I don't figure it out...

Cheers