LPFP support for HPFP rail pressure

doublespaces

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I got a chance to do some pulls in my car finally. Previously I had a bucketless DW400 and my low pressures typically stayed in the 50's/60's or better even with the overdrive installed. Once I got the OD tables inserted into my existing tune, there was no improvement on the rail pressure but I did notice my low pressure did dip into the 40's for the first time that I could recall.

Ken suggested something might be wrong with my fuel pump and as you can imagine this is the last thing you want to hear when other people are making more power with the same pump. To put the issue to bed I decided to get the EOS fuel system with a single Walbro 525 and the BPM-4 EKP. With these mods done and no other changes (Unless you count a transmission cooler) I finally got a chance to go back out tonight two months later to see the difference. This just goes to show there is definitely some voodoo going on with the EKP as well some apparent sensitivity to low pressure supply. What seemed like a LP fuel system that was keeping up 'okay' turns out that one of these pieces was the entire problem.

Just because your LP sensor says 50+ which seems to have been the gold standard for an OK low pressure system, this doesn't mean everything is working correctly. There must be something occurring with the high pressure when it believes the low side isn't or won't be able to keep up with fuel demand. If it isn't doing this intelligently, then I can say in my case the OD tables won't work unless everything is functioning on the low side.

Before LP fuel upgrades:
 
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doublespaces

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After Walbro 525 + BPM-4 (Same exact tune):



You'll notice the LP does go back into the 40's but it is sustaining a much higher rail pressure. I've also not done any BPM4 logging yet or tried dialing any of this in so there is definitely more to work on. This is probably the first log I'll send Ken that didn't have "Return to customer" written all over it. Thanks to Ken @WedgePerformance and Steven @Sbrach for taking care of this for me. This is the first time I've seen my rail pressure look decent and I've been fighting this for years.

So the solution was one or a combination of:

BPM-4
EOS Fuel System
Walbro 525
Transmission Cooler
Transmission Cooler Fan
Waiting for months
Act of God


So clearly its one of the first three, you pick.


FYI: This is on E54 and a 6266 Gen2
 
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doublespaces

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Just made an adjustment because I actually had the wrong 'before' log shown.
 

yuli8466

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I got a chance to do some pulls in my car finally. Previously I had a bucketless DW400 and my low pressures typically stayed in the 50's/60's or better even with the overdrive installed. Once I got the OD tables inserted into my existing tune, there was no improvement on the rail pressure but I did notice my low pressure did dip into the 40's for the first time that I could recall.

Ken suggested something might be wrong with my fuel pump and as you can imagine this is the last thing you want to hear when you hear about other people making more power with the same pump. To put the issue to bed I decided to get the EOS fuel system with a single Walbro 525 and the BPM-4 EKP. With these mods done and no other changes (Unless you count a transmission cooler) I finally got a chance to go back out tonight two months later to see the difference. This just goes to show there is definitely some voodoo going on with the EKP as well some apparent sensitivity to low pressure supply. What seemed like a LP fuel system that was keeping up 'okay' turns out that one of these pieces was the entire problem.

Just because your LP sensor says 50+ which seems to have been the gold standard for an OK low pressure system, this doesn't mean everything is working correctly. There must be something occurring with the high pressure when it believes the low side isn't or won't be able to keep up with fuel demand. If it isn't doing this intelligently, then I can say in my case the OD tables won't work unless everything is functioning on the low side.

Before LP fuel upgrades:

if you can keep the rail pressure good. why do you care about the lp pressure. DW400 flows much more at lower pressure ,it can supply well .

i guess you just want the LP pressure number looks good..
 

gmagnus7

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Dec 3, 2018
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if you can keep the rail pressure good. why do you care about the lp pressure. DW400 flows much more at lower pressure ,it can supply well .

i guess you just want the LP pressure number looks good..
Correct me if I'm wrong but he's showing you that it clearly wasn't keep up with actual hard data. Simply changing the LPFP bumped the HPFP up 1000 psi at 6800 where it was running out of steam.

Also I was under the impression that 50-60's are actually low, and the system/HPFP as a whole was designed around 72psi?
 

Rob09msport

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Oct 28, 2017
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I dont believe it was the pressure being to low but correct me if I'm wrong. These new tables have to do with inlet valve so the stock ekp spikes to 80 sometimes higher this if sustained prob isbt an issue but I would think that it could cause the hpfp to expect more fuel then it gets. I don't believe psi is the issue bit more fluctuations. My hpfp stays rock solid with or without the tables but when my lpfp bounces around it crashes to 1000 and I usually have the issue of to much fuel psi on low side not to little. I believe a better solution is an external fpr for people having this issue .
 

BOosted 335i

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Jun 1, 2017
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After Walbro 525 + BPM-4 (Same exact tune):



You'll notice the LP does go back into the 40's but it is sustaining a much higher rail pressure. I've also not done any BPM4 logging yet or tried dialing any of this in so there is definitely more to work on. This is probably the first log I'll send Ken that didn't have "Return to customer" written all over it. Thanks to Ken @WedgePerformance and Steven @Sbrach for taking care of this for me. This is the first time I've seen my rail pressure look decent and I've been fighting this for years.

So the solution was one or a combination of:

BPM-4
EOS Fuel System
Walbro 525
Transmission Cooler
Transmission Cooler Fan
Waiting for months
Act of God


So clearly its one of the first three, you pick.


FYI: This is on E54 and a 6266 Gen2
How about trying a e40 ethanol mix.its 100 octane at that point and see how it goes.
 

martymil

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It does not matter that the dw400 flows more at low pressure, its the lack of lpfp pressure is the problem with the HPFP as it has very restrictive inlet passage.

Turning the pressure up to 80psi and keeping it there would be optimal for a single HPFP to keep it happy.

The wild swings of the lpfp can be a problem for the dme and how it controls the HPFP especially when it sees big dips in the lpfp pressure.

They are easily fixed as I addressed this subject before.
 
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doublespaces

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if you can keep the rail pressure good. why do you care about the lp pressure. DW400 flows much more at lower pressure ,it can supply well .

i guess you just want the LP pressure number looks good..

Because I'm barely tickling this turbo at 20 psi and I intend to turn the boost up.

Correct me if I'm wrong but he's showing you that it clearly wasn't keep up with actual hard data. Simply changing the LPFP bumped the HPFP up 1000 psi at 6800 where it was running out of steam.

Also I was under the impression that 50-60's are actually low, and the system/HPFP as a whole was designed around 72psi?
It is, but if you go back you'll see people say that 50 psi Low pressure and 1500 psi high pressure is considered the minimums. In my personal opinion, 50's are too low given an otherwisee healthy fuel system.

I dont believe it was the pressure being to low but correct me if I'm wrong. These new tables have to do with inlet valve so the stock ekp spikes to 80 sometimes higher this if sustained prob isbt an issue but I would think that it could cause the hpfp to expect more fuel then it gets. I don't believe psi is the issue bit more fluctuations. My hpfp stays rock solid with or without the tables but when my lpfp bounces around it crashes to 1000 and I usually have the issue of to much fuel psi on low side not to little. I believe a better solution is an external fpr for people having this issue .

Do you have a graph of a low pressure pump that was flat lining when pushed past the limit? The only ones I can recall from recent memory are very spikey.

How about trying a e40 ethanol mix.its 100 octane at that point and see how it goes.

E54 is what I get from the pump and I won't be mixing anything because I'm lazy. Also, my fuel system has room for two more pumps so if I do anything I'll just slip another 525 in there since they cost barely anything compared to the headaches I can avoid trying to min/max one pump. Since I have the BPM4, I might as well run two pumps anyway.
 
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Jeffman

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The wild swings of the lpfp can be a problem for the dme and how it controls the HPFP especially when it sees big dips in the lpfp pressure.
So there’s some kind feedback loop between the LPFP control system and the HPFP control system? If so, this clearly calls for HPFP inlet control tuning.
 

martymil

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When the dme see's dips below what it doesn't like it will intervene, keeping the pressure steady helps

I use to get random missfires when the lpfp pressure dipped
 
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martymil

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Something happens that causes the car to missfire when the wild spikes happen, dont know exactly what the dme does but throws plausibility pump errors.

Stopped the swings and no errors or missfires.
 

EthanolTurbo

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How about trying a e40 ethanol mix.its 100 octane at that point and see how it goes.

E40 is not 100 octane. E85 is 113-115 octane on a boosted car, so E40 must be 106-109 octane by my reckoning. I don't know why people still claim E85 is 105 octane when it's been proven time and again that it beats 116 octane race fuel IIRC.