[proTUNING Freaks]

Almost every time we tune an E85 blend car with or without an LPFP upgrade people want to know what they need to look out for on the HPFP and LPFP sides pressure wise and what is considered normal and where they should start to worry and look into issues.

In general you want to log your short term fuel trims (STFTs) on both banks as well as long term fuel trims (LTFTs) on both banks and ensure that they're not being maxed in either direction. Positive trims (up to +34%) indicates the DME is working harder than the map/fuel system are set up for and its doing additional work on its own (closed loop fueling) to compensate and add fuel. Once the max of +34% is reached then closed loop fuel control becomes maxed and you'll start to see your Lambda (AFR) actual start to lean out beyond target possibly resulting in misfires and other issues. While its rare to detonate these motors due to this issue (we haven't heard of such issue yet on the N54 that directly correlated to trims maxing out) it certainly isn't a good idea to be running the car with a maxed out closed loop system.

The same thing can happen in the opposite direction if say your tune is set for an E50 blend but you're running MS109 race gas. While the tune may not knock given fuel scalar settings your log will start to show fuel trims going the opposite way potentially maxing out at -34%. This is when you'll also start to see your Lambda (AFR) actual start to go richer than target, again, incurring misfires and similar issues.

Coming back to the fuel pressures at the LPFP and HPFP as a very high level general guideline/rule of thumb, you don't want to see your LPFP dropping into the 40psi range. 50s can be ok provided your HPFP is not dropping out. We've seen cars run without any issues on as low as 1200psi at the HPFP but we don't recommend that at all. We recommend 1500psi as the bare minimum target. If your HPFP Actual pressure is dropping below 1500psi anywhere its time to start looking into either adjusting your tune to be less aggressive or upgrading the LPFP system if you haven't done so already or adding supplemental fueling via a secondary rail or similar.

[TheYuriPanda]

Finally! This will be so much help for people looking to jump into the E85 world and eliminate "blank" questions. Plus terry would be thankful for this im sure haha.

[924er]

I needed this!!!

Thanks!

Here is a log in case anyone wants to give an opinion. According to what I read above my log looks okay. 4 gallons e85 with 91 octane stage 2 aggressive +

My STFT goes up to 29+

http://datazap.me/u/moswissa/stage-2...a=1-7-16-17-22" rel="" target="_blank">http://<a href="http://datazap.me/u/...7-16-17-22</a>

[Welterweight]

Thanks for sharing the knowledge!

[ImGone92]

Does the cobb v3 show fuel levels I need to see if my pressure is dropping, was recently tuned by ptf and now having alot of issues with my fueling. ...car shut off with me 2 days ago and gave code for low fuel pressure. Why would this keep happening? Hpfp changed at bmw 2 months ago. I used to run cobb stage2+ aggressive, no issues. Pls any help would be great, thanks guys

[proTUNING Freaks]

Originally Posted by ImGone92

Does the cobb v3 show fuel levels I need to see if my pressure is dropping, was recently tuned by ptf and now having alot of issues with my fueling. ...car shut off with me 2 days ago and gave code for low fuel pressure. Why would this keep happening? Hpfp changed at bmw 2 months ago. I used to run cobb stage2+ aggressive, no issues. Pls any help would be great, thanks guys

Please email us at support@protuningfreaks.com about this issue and we can take a look at a log. It can be any number of reasons including weak LPFP, HPFP or maybe not even related such as coils/plugs/injector.

[Nonecure]

Does anyone know how to log lpfp pressure using OFT, BMWhat, or DCAN cable?

[Jklad]

This is great info for e85.

My LTFTs on 93 octane when cruising around town (normal driving) are hangout out between 18.5% to 22% on both banks. Could this indicate, or cause, an issue?

[jlcf22]

thanks for this great info been wondering about this

[CHECKERED]

Originally Posted by proTUNING Freaks

We've seen cars run without any issues on as low as 1200psi at the HPFP but we don't recommend that at all. We recommend 1500psi as the bare minimum target. If your HPFP Actual pressure is dropping below 1500psi anywhere its time to start looking into either adjusting your tune to be less aggressive or upgrading the LPFP system if you haven't done so already or adding supplemental fueling via a secondary rail or similar.

I would like to add a second opinion:
under ideal conditions the HPFP should be at 1500psi, however 1200-1350psi values are acceptable as long as they are not accompanied by lean AFRs or knock events.

values below 1200psi should be avoided at all cost.

[kaigoss69]

Does this rule of thumb apply no matter what fuel is used? How about 93 octane?

[Digitalism]

Yes it applies to whatever fuel you are using.

[Digitalism]

The use of E85 places more stress and demand on the fuel system, and so any weaknesses quickly show up.

[mojobmw_e90]

So how does one change the graph reading on the jb4 program so it can be read easier

[Dmacc]

Originally Posted by mojobmw_e90

So how does one change the graph reading on the jb4 program so it can be read easier

Upload your logs to datazap if you're having trouble reading them in the jb software.

[mojobmw_e90]

Originally Posted by Dmacc

Upload your logs to datazap if you're having trouble reading them in the jb software.

I know how to read it but instead of it saying 1500psi it was 1.5xxxxxxxx. Is this the same?

[shushikiary]

here's a log of mine on 100% E85, after a 3rd to 4th shift my pressure momentarily drops to 1000 PSI, but then climbs back up to 1800 almost immediately. The LPFP pressure seems to jump up and down a lot but the AFR's and fuel trims look great...

So given your statement about under 1000 psi, is that for a minima, or is that for a continued period of time, or if it goes low and you see some issues with AFR?

http://www.datazap.me/u/shushikiary/...=0&data=2-9-13

[proTUNING Freaks]

Originally Posted by shushikiary

here's a log of mine on 100% E85, after a 3rd to 4th shift my pressure momentarily drops to 1000 PSI, but then climbs back up to 1800 almost immediately. The LPFP pressure seems to jump up and down a lot but the AFR's and fuel trims look great...

So given your statement about under 1000 psi, is that for a minima, or is that for a continued period of time, or if it goes low and you see some issues with AFR?

http://www.datazap.me/u/shushikiary/...=0&data=2-9-13

Your HPFP looks fine, no issues there. Through the shift the DME is cutting fuel and ignition and its normal to see the HPFP pressure drop at the shift.

Your requested and actual loads are quite a bit away from each other meaning the car is undershooting in terms of where its asking to be boost wise. Suggest your tuner looks over your logs and advises accordingly. Tuning may need adjustment if you're at altitude or you may have a boost leak. Hard to say as you haven't logged WGDC % in this log.

Let us know if any other questions at all.

[shushikiary]

Yea 5000 foot altitude makes it impossible to hit boost target To keep 12 PSI at 6000 RPM it runs in the mid 60's for WGDC.