Z4 LPFP Sensor Retrofit

Jake@MHD

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As the title states, is installing and running a LPFP sensor something you Z4 guys would be interested in? I believe I figured out how to get it active on the DME side.

Without a sensor, it can only control the LPFP open loop via a hardcoded map based on pump data gathered in testing. Adding the sensor allows the PI controller for the pump to accurately target the pressure set point, as well as log the low pressure psi value.
 

KevinC39

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E series N55 guys don't have a sensor either. Might be all the N55s but figured the early E series N55 DME might be similar at least.
 

NoQuarter

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With my S55 pump project, I have a lpfp sensor already installed in the fuel line. I just need to make a harness for it to try it out.

I like the idea to be able to measure the lpfp pressure
 
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fmorelli

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Ditto. Having that sensor measurement is definitely desirable! Thanks for asking.

Filippo
 

doublespaces

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Interesting, so diagnosing fueling issues can be slightly more difficult in these cases. Anyone know why they removed it? Static table worked good enough?
 

Jake@MHD

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Let me know once someone gets one installed and wired in, I'll send you the DME changes. If it works as expected, I can get it added to MHD as a flash time option.
 

fmorelli

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So while we are on this subject, I've never understood a number of things around this:
  • Why did BMW run two fundamentally different lift pump designs for the same power plant?
  • What are the trade-offs +/- of the traditional E82/E90 LPFP control vs the E89 full-on approach?
  • Why is the Z4 considered "stage 2" (better) than the E82/E90 LPFP setup, coined by @BQTuning (Dimitri) if I recall.
I've never seen this explained, and I certainly don't know the answer. Just tagging a few folks that may have a clue on this. @WedgePerformance @BQTuning @berns @NoQuarter @Hydra Performance

Filippo
 
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NoQuarter

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Ha... This is from the E89 wire diagram showing the LPFP sensor that doesn't exist

Linky

LPFP Sensor.jpg
LPFP Sensor 2.jpg
 
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fmorelli

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Ha... This is from the E89 wire diagram showing the LPFP sensor that doesn't exist
Which adds to the confusion. Not the first time BMW literature has been incorrect, though. Funny, I thought you had mistyped. I went to the E90 ETK, then the E89 diagram, and much to my surprise ... nope ... Jim got it right. lol ...

Filippo
 

BQTuning

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@jyamona can you make the changes "only" so we can log the LPFP sensor if installed and not changing how DME controls fuel on the Z4 or the DME not being reliant on or looking for it? If yes, Im down for it.

@fmorelli the fueling setup could have been modeled after the GT3/GTE fueling setup with the P65B44 v8 in the E89 chassis. When it boils down, it has to do with the LPFP setup. The M6 GT3 does not have a LPFP sensor either from the looks of it

https://www.realoem.com/bmw/enUS/showparts?id=9082-EUR---MOSP-BMW-M6 GT3&diagId=16_1308

https://www.realoem.com/bmw/enUS/showparts?id=9082-EUR---MOSP-BMW-M6 GT3&diagId=13_1991

The Z4 may have very well inherited the GT spec fueling setup. I checked the M4 GT4 and it does appear to have a LPFP sensor if the info is accurate but that must have been needed for the dual HPFP setup.
 

Jake@MHD

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Why would you not want the PID feedback loop for controlling pressure? I think once you log it especially on upgraded pumps you'll see it's not very smooth. Speaking of, I do need to add the lpfp PID tables to the xdfs.
 
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NoQuarter

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I also wonder if will see any cyclical pressure surges from the HPFP on my S55 pump setup. If my CAM timing is off just a bit?