N54 (E87) LPFP psi low??..

digitalashley

Private
Apr 8, 2019
40
Hi everyone,

I have gone from a stock 135i (N54) low pressure fuel pump due to low psi (52-42psi) readings at idle and throughout RPM range (rail pressure would drop and cause limp mode), to a walbro 450 and have retained the bucket and Venturi to keep it close to stock as possible and hopefully food my low psi issue..
I get a 2AAF fuel pump plausibility error at times.
Haven't really driven car yet as build has had stuff to complete first.

After installing the walbro pump I've notice via mhd the LPFP psi starts off with 49psi after a minute or so the psi drops to 39psi.
When idle the fuel rail pressure sits at 700ish which seems to me as fine?
When trying to log some information I see the HPFP psi on rail drop along side the LPFPs psi.
However the rail pressure seems to me within okay limits like 3000-1800psi as the rpm increase.

I currently have;

Inlets 2"
DCI filters
Vrsf outlets slightly modified for RHD
Hybrid turbos via eBay seller. TD04L 17T billet.
5" intercooler
Larger engine oil cooler
Walbro 450 pump


I haven't tried a new fuel pressure sensor yet.
I'm wondering it it'll be a tune based issue as it's currently a tune I've made based off v8 baits spreadsheet and logs before the donor 135i was crashed ( stock turbos then).
LPFP with stock pump was fine before the donor car was crashed. Since the engine swap haven't had any luck with the psi . Car doesn't throw any limp mode codes so far.

Does anyone else have some ideas that might help be fix this or is it a not issue?? I'm worried that I shouldn't drive due to this mostly.

Thanks forum


Here's a datazap link for a log to Reference
 

martymil

Captain
Sep 6, 2017
1,256
Down Under
As long as you code it, but its either your lpfp sensor or your FPR in the LHD fuel tank hat is shot as I've seen these fail as most are over 10 to 12 years old now.

I remove them and replace them with a bolt and run an external adjustable FPR.
 

digitalashley

Private
Apr 8, 2019
40
I just paid for the sensor and a couple other items. So I'll see how we go once I put it in.
The FPF might be as I had a e87 n46 engine FPR in there as I thought they were the same and that would sit at 52psi on idle. where the e82 FPR sits at 52 psi before any throttle input then after sits at 42psi.

Replace them with a bolt?
 

martymil

Captain
Sep 6, 2017
1,256
Down Under
Yep pull the fpr out from the factory rhs fuel tank hat and return pipe and get an appropriate bolt to suit, put a few turns of plumbers tape on the threads and screw it in where the factory fpr presided.

Now install an inline fpr on the drivers side under the car and run a return line to the rhd bucket where the lpfp is, you will need to drill a hole in the hat and install a fitting just like the stage 3 pump has.

You will need a fpr that can handle over 100 psi and set it for 75 psi static pressure when car is not running. Easiest way is to use protools to prime the lpfp to set pressure.
 

digitalashley

Private
Apr 8, 2019
40
An update to my issue.

I have replaced the LPFP sensor.
New regulator in left side of tank.

I did test my setup without the LPFP's top hat on and noticed a leak from a fitting. So have swapped fittings around and tested again with no leaks now. Still same pressure issues (52-37psi).
I grabbed my other cars ekp3 unit to test. Car ran and the psi was a steady 52psi so better than the other ekp3 unit.
After a matter of minutes I turned car off and removed the ekp3 unit I was testing and noticed it was really hot.
So that has me thinking maybe it's the ekp3 getting so hot due to something?? But in turn dials back amps/voltage...
I'm thinking about a diy with heatsinks and a small PC style fan. But might test with a fan and the ekp3 cover off to see what happens..
 

martymil

Captain
Sep 6, 2017
1,256
Down Under
Possibly be a faulty pump or an internal fuel leak somewhere because your not hitting fuel target the ekp3 is running your pump at 100% duty cycle causing it to heat up.

I run the new Walbro 535 with no overheating issues on my ekp3 and hit target no problem which is a much bigger pump that draws a little more current than a 450.

Have you tried priming your pump using protools or any other app that can do that whilst the engine is not running to see what pressure the pump will hold ?
 
  • 1Like
Reactions: digitalashley

digitalashley

Private
Apr 8, 2019
40
You make an interesting point.
It must be over working the EKP, pump could be faulty as I hear people to have issues with walbro.
I did have this psi issue since the swapping N54 into the E87, even with stock pump etc. So I'm thinking maybe there is a daily somewhere still. Can't think of where... Hmm.

I do have ista d software can't recall what for pump things I can test with that but recently installed pro tools, haven't used yet but might have to give it a go and see. I'm curious to see what kind of results I will get. I assume pressure wise I should see 72psi or close to without engine running?
 

doublespaces

Administrator
Oct 18, 2016
8,228
AZ
Is there a way to see Input Duty Cycle for the LPFP? I know with the BPM4 you can see input and output duty cycle. There are times when I've seen my LPFP drop but when I go to the logs, the DME is actually telling the EKP to lower duty cycle. The question is, why can't we log this in MHD? I think it is assumed the EKP is 100% DC at WOT, but (I'd need to double check my logs) I think there are times when this either isn't true or behaves unexpectedly. Instances when the tune is telling the EKP to pull back on the LPFP even when it isn't at the 72PSI we all expect to see.
 
  • 1Like
Reactions: digitalashley

digitalashley

Private
Apr 8, 2019
40
I'll attach an image of what ista d let me see .
Has actual and Target speeds.
IMG_20200205_121953.jpg


I'm really unsure why I have the issue as I've replaced pretty much everything.
But I'll throw my stock pump back in just to test it again and look at my diy stage 2 setup with the walbro. But it's as if there is fuel being lost somewhere and causing the lower psi.. I had a leak on one of the fittings and fixed that so I worry it's to do with the Venturi setup maybe I'll redo that also Incase there is a leak, maybe plug that line off for a test also.
Fingers crossed I find something
 

martymil

Captain
Sep 6, 2017
1,256
Down Under
Unless you messed with the venturi it won't be an issue, id throw in the stock pump and test idle pressures first, it's most likely something so simple you overlooked you'll kick your self later.
 

digitalashley

Private
Apr 8, 2019
40
Here's a picture of my setup of the Venturi.
Yeah I bet it's something that haha . As long as I figure it out I'll be happy.
IMG_20191223_155511.jpg

Since this photo was taken I have added an extra zip tie at the rear section of the Venturi incase. So I'm thinking maybe it's where the little clamp is../ hoping that's it haha.
 
Top