LPFP behaviour after stage 1 upgrade

CantSitStill

Specialist
Jul 22, 2022
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Hi Guys,

I have just upgraded my LPFP to a stage 1 in line in tank (walbro 255lph). Anyway I did it because I was dropping down to 49psi at WOT and the rail was draining. It solved the issue however, to start with after the upgrade I was holding 73psi all the time. Fast forward a month and now I'm back down at 60-66psi at WOT or idle. Rail pressure is all good but I don't understand why its not giving me the 72-73 psi I'm supposed to get especially at WOT.

When I do a cold start it will give me 73psi for about 10 secs then it backs off to 66psi as if the fuel pump controller is slowing the pump down. I have yet to test the voltage. I don't think it can be the new pump since it primes to 73psi OK and runs fine for 10 secs.

Any suggestions what is going on? I'm more worried about the WOT situation as its dropping to 60psi so any more boost and I will probably drain again.

Does anyone else see the pressure going lower a than 72psi with an upgraded pump, could this be normal?

Should also mention I reset the Hpfp adaptations as suggested on other posts but never made a difference.

Thanks
 
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CantSitStill

Specialist
Jul 22, 2022
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Update: measured the pump voltage at idle with 65psi and was exactly 6.5volts. No idea if this is normal

Edit: did a test with ISTA. It ran the pump at full wack to start at about 11.5v. I could not measure the pressure but assume would be much higher becuase its 5v more. Anyway in the next step it runs it at 6.5v with the engine running and asks what the pressure is so I just put in 65psi as above and it said that's OK. So it seems it does not always target 72psi as I read since the procedure was happy with 65psi (to confirm I tried 45psi and it said thats a fail). ISTA never said anything about 72psi. It did mention at the end that if I'm still having issues to delete the EKPM low pressure adaptations which I can't find a procedure for anywhere in ISTA.

All I can think is that the 72psi is the max pressure if the regulator is OK but the DME can target lower than that if its happy. I will just need to check my WOT conditions and maybe find a way to reset these adaptations it mentions
 
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SLOWESTN54

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Feb 9, 2021
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Oscillations are normal for this platform, unless you install a external FPR and install a full return style system, or you can use a BMP4. If the oscillations are really bad you could try installing a new EKP or a new in tank filter/regulator.
 

CantSitStill

Specialist
Jul 22, 2022
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Oscillations are normal for this platform, unless you install a external FPR and install a full return style system, or you can use a BMP4. If the oscillations are really bad you could try installing a new EKP or a new in tank filter/regulator.
Its not so much an oscillation, the logs are smooth. It's the DME/EKP targeting a lower pump voltage/pressure for some reason. Its only running 6.5v at idle. Not tested the voltage at WOT but i assume it must be increasing the voltage to keep the pressure at 62-65psi and increase the flow to match the HPFP flow rate. What i dont get is why its not hitting 72-73psi like you see in normal logs. From my ISTA tests it suggests this is normal and an OK pressure. I know the rail drain only really happens about 50psi or below so i guess i just need to keep an eye on it
 

wheela

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Jun 4, 2021
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Its only running 6.5v at idle.
I'm curious, how are you measuring the voltage? The pump runs on a duty cycle, so I don't know if a regular volt meter will give you an accurate voltage reading; it may report low due to the signal cycling on and off rapidly. I'm sure you could get an accurate reading with an oscilloscope though.
 

carabuser

Lieutenant
Oct 2, 2019
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What ROM version are you on?

I can send you a file that will let you log the PWM output to the pump along with the pressure the DME is targeting (which should always be 72.5PSI).

What is your car? Z4 LPFP controls open loop so you won't see it chase the setpoint like the 335i does.
 
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CantSitStill

Specialist
Jul 22, 2022
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What ROM version are you on?

I can send you a file that will let you log the PWM output to the pump along with the pressure the DME is targeting (which should always be 72.5PSI).

What is your car? Z4 LPFP controls open loop so you won't see it chase the setpoint like the 335i does.
Its a 335i 2007. No idea what ROM im on, would need to look. Do you mean ROM for the EKP? Sure if you can send something that would be great!
 

CantSitStill

Specialist
Jul 22, 2022
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I'm curious, how are you measuring the voltage? The pump runs on a duty cycle, so I don't know if a regular volt meter will give you an accurate voltage reading; it may report low due to the signal cycling on and off rapidly. I'm sure you could get an accurate reading with an oscilloscope though.
I was using a voltage meter to read it so it could have been a bit low but the full wack signal ISTA sent got up to 11.7v i think so at least i know the EKP is lowering the pressure/signal and not maxing out/failing pump. I think my meter has a PWM setting so i can try that as well. I also have leads with a capacitor so they should show me what voltage the PWM signal is supplying.
 

carabuser

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Oct 2, 2019
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Unzip that file and copy it to the MHD root directory. That will add 2 extra parameters into the logging channels. LPFP PWM and LPFP Target. Add both of those to your next log along with the LPFP reading.

That will tell you exactly what the LPFP is doing and what the DME is asking it to do.
 

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CantSitStill

Specialist
Jul 22, 2022
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Unzip that file and copy it to the MHD root directory. That will add 2 extra parameters into the logging channels. LPFP PWM and LPFP Target. Add both of those to your next log along with the LPFP reading.

That will tell you exactly what the LPFP is doing and what the DME is asking it to do.
Very nice! Thanks. I will try it tomorrow. I got drunk last night and the car was left in town!
 
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CantSitStill

Specialist
Jul 22, 2022
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OK I did it. And.... Its weird MHD reports everything perfect. The JB4 reports 66psi when MHD is reporting 72.5psi. So basically the JB4 is reading wrong or its slowing the pump down, could be possible as it changes the rail pressures I think. Anyway probably nothing to worry about
 

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carabuser

Lieutenant
Oct 2, 2019
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OK I did it. And.... Its weird MHD reports everything perfect. The JB4 reports 66psi when MHD is reporting 72.5psi. So basically the JB4 is reading wrong or its slowing the pump down, could be possible as it changes the rail pressures I think. Anyway probably nothing to worry about
JB4 mis-reports load which causes the DME to request less fuel from the EKP. Best to just leave the JB4 disconnected, it's not really useful anymore.
 
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CantSitStill

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Jul 22, 2022
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JB4 mis-reports load which causes the DME to request less fuel from the EKP. Best to just leave the JB4 disconnected, it's not really useful anymore.
I use it mainly so I can tune the car myself with the BEF's and not need to attempt the boost part of the tune. I might pay wedge for a 5th tune if I get the cash again and I'm happy with how the car is dialed in on the jb4. Can only get better with a flash tune!
 

CantSitStill

Specialist
Jul 22, 2022
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Unzip that file and copy it to the MHD root directory. That will add 2 extra parameters into the logging channels. LPFP PWM and LPFP Target. Add both of those to your next log along with the LPFP reading.

That will tell you exactly what the LPFP is doing and what the DME is asking it to do.
Thanks for your help dude!
 

jomo

New Member
Aug 13, 2023
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I’m trying to log the additional parameters by inserting the unzipped file. After I place the unzipped file in the MHD folder (I think this is considered the root folder), I don’t see the additional parameters in options. Any help or ideas? Am I placing it in the right folder?

I’m having a fueling problem as well where my low pressure hovers around 49-51psi at all times.
 

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