N54 having LPFP spikes over 110psi!

[alvinhobh]

N54 having LPFP spikes over 110psi!

2007 335i e92
Fuel-it stage 3 LPFP
550 cc PI
AIC2
Motiv- FF sensor
Running e85

In the process of tuning my car, noticed the LPFP pressure was all over the place, dropping below 40 and spikes over 100psi, so I decided to replace the following:

HPFP ( FCP lifetime warranty so why not)
HPFP sensor
LPFP sensor
Both LPFP filters
Driver side tank filter/ regulator tank
Removed and blocked off the stock FPR
Install an external FPR
Replaced the EKP ( used on from Ebay, coded with protool)

Pressure doesnt drop as lowe as before but still like crazy spikes! Tuner is working with me on this, giving me above and beyond support. He lowered the boost target so we can how things behave and I don't need help on analyzing anything in the log, but I wanted to put it out here and see if anyone has ever experienced the same issue with the LPFP spikes.

Hide legend Reset zoom

 

[noorj]

Thanks @martymil

I used my old sensor and left the new one I bought in the original position.

Yeah I'll likely do that, but want to get an adapter fitting for the metric to 1/8" NPT conversion

 

[martymil]

I get rid of the hard line and lpfp sensor as the metal hard line turns are very restrictive and use a Speedflow 171-06-14-BLK hpfp adapter and you can connect a 6an fuel line directly to the hpfp pump, this should net you an extra 150psi in the hpfp rail.

 

[noorj]

Hey guys, I changed around my fuel system to add an external regulator and have it routed the dead-head way @martymil showed earlier but now I'm seeing something weird. Regulator is not hooked up to boost reference, and set to ~72psi at engine idle and stays there when driving around until I do a pull (turned down to like 20psi for now) then the pressure stays at 90psi for the rest of the drive until I shut ignition off and restart the car. I'm convinced it's not the regulator as the reg doesn't know ignition, so I think it's either my second pump (triggered off a hobbs switch) staying on or something the EKP is doing. Any thoughts or ways to fix this? I did verify pressure is following what the LPFP sensor says with a mechanical gauge

 

[martymil]

Did you remove the factory reg out of the tank.

Did you set static reg pressure to 75psi when engine is off and run a return line back to the tank and put the lpfp sensor on the reg pressure reference port

If you did there is something wrong with the reg as there is no way the pressure would go any higher than the pre set

 

[noorj]

Yeah factory regulator & fuel filter is removed. 72psi set with engine off and it's a "dead-head" system exactly like your schematic just with a check valve in after the 10micron filter as well. I haven't moved the LPFP sensor yet, but I did confirm both the mechanical gauge on the regulator and the LPFP sensor read 72 with engine off and idling but then after a pull both read 90. I can check the regulator out, but how would it "know" when I do a pull and run 90psi until I ignition on/off again? I'm going to test it out on lower boost with the secondary lpfp relay unplugged, and see if it still does this.

 

[martymil]

Reg has to be set to 75psi with engine off

 

[doublespaces]

Alright, time to throw my hat in this ring.

I have an 8AN feed line up to a 6AN Y. One side goes to my flex sensor then the HPFP and the other goes to PI. No return line. In tank radium FPR.

I feel like I suffer from something similar, low pressure can drop a ton but rail pressure looks good, typically:

Going forward I have to decide between a return-less and return system:

For each configuration there are various options I was thinking about:

• Dead-head FPR:
  • Sensor on B, damper at C
  • Sensor on X, damper at C
  • Sensor on FPR, damper on A
  • Sensor on FPR, damper on C
  • Sensor on FPR, damper on C and Y
• Bypass FPR:
  • Sensor at B, damper at C
  • Sensor at X, damper on C
  • Sensor before A, damper at A
  • Sensor on FPR, damper at Z
  • Sensor on FPR, damper at C

Since PI flow is affected greatly by the LPFP, I wasn't certain on the best place to put the sensor/damper. There are obviously a lot of different combinations here, I would appreciate feedback on which one you guys think would be optimal for return and returnless.

 

[doublespaces]

I also noticed that Radium offers a FPR/Damper combo:

FPR-D, Fuel Pressure Regulator-Damper

I was hoping to be able to simply put this after the PI rail and call it a day (equivalent to: sensor on FPR, damper at Z )

 

[martymil]

On the dead head system you want the LPFP sensor on the reference port of the FPR opposite the return line and the damper at A

Bypass FPR you want the LPFP sensor on the reference port of FPR and damper at Z

Do not connect boost line to FPR on either system.

 

[doublespaces]

On the dead head system you want the LPFP sensor on the reference port of the FPR opposite the return line and the damper at A

Bypass FPR you want the LPFP sensor on the reference port of FPR and damper at Z

Do not connect boost line to FPR on either system.

Thank you for your input, this is what I was hoping would be the case. Any thoughts on that Radium FPR/Damper combo? Seems like a compact unit. How can I tell if it's a bypass or dead head regulator?

Edit: it specifically says 'bypassed' so I'm going to assume it's what I want for a return setup:

Two interchangeable orifices are included to match the amount of fuel bypassed for the application

 

[martymil]

I prefer having the FPR and Damper separate as you can move things around or reconfigure if it doesn't work.

You can also move the damper closer or further away from problem areas to ascertain where it will work best.

 

[doublespaces]

On the dead head system you want the LPFP sensor on the reference port of the FPR opposite the return line and the damper at A

Bypass FPR you want the LPFP sensor on the reference port of FPR and damper at Z

Do not connect boost line to FPR on either system.

So I setup a return line, sensor still in the stock location. Spikes are still there like usual.

I can move the sensor to the fpr without much issue. But there isn't enough clearance to place the damper at Z. I'll have to put it at A

 

[iminhell1]

Dampner should be on feed in a return system.
Sensor should be on return ... reason for this is because you really don't need the resolution it's capable of. I still don't understand why people think you do. It honestly just needs to read at startup only. Maybe once a gallon thereafter. The mix isn't going to swing enough to make any difference. And if it does while you're WOT, you're already F'd. Nothing is going to save you, there's no failsafe table. Just the mix table.

 

[GreyNBlueE92]

I don't have a return setup but i have lost fuel pressure going wot and the car cut boost and injection until fixed/restarted. I believe it saved my motor or i was just extremely lucky. For this reason i think the sensor should stay on the feed line, so it goes into limp mode before it goes lean instead of after. This was when the rubber "submersible" fuel hose burst on my diy stage 2 when I started messing with ethanol.

 

[doublespaces]

Dampner should be on feed in a return system.
Sensor should be on return ... reason for this is because you really don't need the resolution it's capable of. I still don't understand why people think you do. It honestly just needs to read at startup only. Maybe once a gallon thereafter. The mix isn't going to swing enough to make any difference. And if it does while you're WOT, you're already F'd. Nothing is going to save you, there's no failsafe table. Just the mix table.

Are you talking about the flex fuel sensor or the LPFP sensor?

I don't have a return setup but i have lost fuel pressure going wot and the car cut boost and injection until fixed/restarted. I believe it saved my motor or i was just extremely lucky. For this reason i think the sensor should stay on the feed line, so it goes into limp mode before it goes lean instead of after. This was when the rubber "submersible" fuel hose burst on my diy stage 2 when I started messing with ethanol.

How are we defining return line? Because I don't see a big difference as long as the LPFP sensor is on the 'return' line after the PI rail and before the FPR. Placing the LPFP sensor after the FPR would not show much or any pressure or relevant data.

 

[GreyNBlueE92]

How are we defining return line? Because I don't see a big difference as long as the LPFP sensor is on the 'return' line after the PI rail and before the FPR. Placing the LPFP sensor after the FPR would not show much or any pressure or relevant data.

I meant after the FPR. Never thought about return from PI rail. I still think the LPFP sensor should be on the feed. So the DME knows if the engine is getting the pressure it needs and can act accordingly, potentially saving the engine.

 

[martymil]

The best place to put it is on the fpr fuel pressure reference port as that's what essentially is controlling and setting the pressure in your fuel system, anywhere else you will see massive swings in pressure due to the di hpfp valve opening/closing rapidly.

 

[iminhell1]

Are you talking about the flex fuel sensor or the LPFP sensor?

Flex Fuel, after. And I only say this based on the potential flow restriction it could pose. I'm told they don't, but like I said about the resolution, it's just not importiant to be at the head of the line.

LPFP Sensor can really be anywhere on the feed line. If there's room a nice spot might be to drill into that Y and put it on the -8 side. Then make a steel cover for the whole thing and bolt it to the bottom of the car.

 

[sch4400]

I prefer having the FPR and Damper separate as you can move things around or reconfigure if it doesn't work.

You can also move the damper closer or further away from problem areas to ascertain where it will work best.

sorry to bring this up .
I need you help.
is this way to solve the spike problem??

 

[martymil]

The damper needs to be where B is or Z

FPR is has to be on the return line same position as in pic and lpfp sensor is on the FPR reference port.

if you have a flex sensor it can be anywhere it really doesn't matter A or Z position.