Erratic low fuel pressure

SCHWARZ_E92

New Member
Sep 3, 2020
4
0
0
Georgia
Ride
2009 335i
Any idea why my fuel low pressure is erratic and dips as low as 58psi??


Im single turbo, full e85 and currently in tuning process with Ken @ wedge
Bucketless dual walbro 450s, yes 2nd pump is supplying fuel when hobbs closes
Phoenix racing manifold with 550cc injectors
Reflex lite PI controller
Stock fuel lines
Fuel pressure regulator is just over 2 years old
 

carabuser

Lieutenant
Oct 2, 2019
849
1
745
0
UK
Ride
Z4 35i & 335i
I'll put together a custom logging map tomorrow that'll let you see the control signal to both the lpfp and the vcv so you get an idea of the cause.

Looking at the log though it just seems to run out of lpfp. Are you sure the pumps are working correctly and there's no leaks?
 
  • Like
Reactions: TheFixer and wheela

SCHWARZ_E92

New Member
Sep 3, 2020
4
0
0
Georgia
Ride
2009 335i
I'll put together a custom logging map tomorrow that'll let you see the control signal to both the lpfp and the vcv so you get an idea of the cause.

Looking at the log though it just seems to run out of lpfp. Are you sure the pumps are working correctly and there's no leaks?
Pretty sure they are working correctly. Last night i pulled the fuel pump fuses, cranked car to get low fuel pressure, then jumped the hobbs switch and the 2nd pump went on and fuel pressure went up. Using a 15psi hobbs switch.

New thing im going to do is hook it up to a switch and jump it mid log and see if that helps fuel pressure just incase the hobbs switch isnt coming on with boost or something.

Dont think there are any leaks or anything with the fuel pump/fpr assemblies that is off. Will double check when i get time
 

nyt

Sergeant
Sep 15, 2019
331
1
289
0
Ride
2010 335xi
I ran into limitations with the stock fuel lines. I now run an additional external feed from one pump which merges before an external filter. I still want to pull out the oem filter and replace the hat, I just haven't had the opportunity to machine one yet :( I'm running two 535s in parallel driven by a bpm4.

Two -6 to a -8 to a Y then -6 to hp and lp rails

6Gbht0P.png


fo4UoTT.jpg
 

SCHWARZ_E92

New Member
Sep 3, 2020
4
0
0
Georgia
Ride
2009 335i
I ran into limitations with the stock fuel lines. I now run an additional external feed from one pump which merges before an external filter. I still want to pull out the oem filter and replace the hat, I just haven't had the opportunity to machine one yet :( I'm running two 535s in parallel driven by a bpm4.

Two -6 to a -8 to a Y then -6 to hp and lp rails

View attachment 74051

View attachment 74052
Id like to do something similar but im trying to figure out the exact fittings and everything i would need

I currently have 2 450s Y into the stock lines. Trying to figure out what i need to run the secondary one externally
 
Last edited: