LPFP all over the place

kulixo

Lurker
May 26, 2020
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3
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Hi!

I tried searching for this topic, but was unable to find a solution.
Having issues with LPFP sometimes diving as low as 45psi.
Here is a log: https://datazap.me/u/kulixo/lpfp?log=0&data=3-4-12-21-25

Running 2x walbro 450. Secondary is triggered by boost, I'm certain that I'm hearing the relay activate.
100% E85
PI

As part of the troubleshooting, I've also done the following:
6AN fuel line to the hardline at engine.
Drilled fuel rail inlet
Removed HPFP filter, bypassed intank-filter and running an inline filter instead (High quality one)
Replaced EKP

I've never seen rail pressure / lambda being actually being affected, but still doesn't feel right.
Any suggestions?
 

carabuser

Lieutenant
Oct 2, 2019
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Z4 35i & 335i
Ideally you need to be monitoring the requested PWM signal sent to the LPFP.

Unzip this file and place it into the MHD root directory. This will then give you access to a parameter called "$ EFPPWM (LPFP Demand)"

Add that to the next log and that will tell you if the reason for the fluctuations is electrical or mechanical.
 

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martymil

Major General
Sep 6, 2017
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Put a fuel damper on the HPFP and your LPFP sensor on the fuel reg if running one, your seeing the pulses from the HPFP opening and closing
to regulate the HPFP rail. A fuel damper will help a lot but you will still see some without moving the LPFP sensor onto the reference port of an aftermarket reg with a return line.
 

kulixo

Lurker
May 26, 2020
15
3
0
Thanks for the suggestions!

Ideally you need to be monitoring the requested PWM signal sent to the LPFP.

Unzip this file and place it into the MHD root directory. This will then give you access to a parameter called "$ EFPPWM (LPFP Demand)"

Add that to the next log and that will tell you if the reason for the fluctuations is electrical or mechanical.

This parameter was very useful, I added it to the latest log: https://datazap.me/u/kulixo/lpfp-2?log=0&data=2-4-13-22-23-24
It's pegged at maximum during WOT, so this would indicate that there is an issue with fuel delivery.

Put a fuel damper on the HPFP and your LPFP sensor on the fuel reg if running one, your seeing the pulses from the HPFP opening and closing
to regulate the HPFP rail. A fuel damper will help a lot but you will still see some without moving the LPFP sensor onto the reference port of an aftermarket reg with a return line.

I tried moving the sensor to start with.
I'm using the stock FPR, but placed the sensor were the return line would go on PI rail.
Some of the fluctuations were removed, but pressure is still a bit low.

I also tried another experiment to try and eliminate causes. I lowered boost to a level where I believe a single 450 would be able to handle. I then disconnected PI and the secondary 450.
In this case, the single 450 simply wouldnt reach the demand: https://datazap.me/u/kulixo/lpfp-3?log=0&data=3-11-20
There are alot less fluctuations though.
Maybe I have to double check all the hardware once more. Or perhaps the 1st pump is simply tired, I'm a bit tempted to try and replace it with a Walbro 520 or 535 while keeping the other 450 as secondary.