Help/suggestions needed for rail pressure dropping

[Baileyboo]

Hello all,

I need some help on an issue I’m having. On WOT my fuel rail pressure is dropping off a cliff on the logs (link). On a WOT pull the car accelerates about 750-1000 rpm then hesitates and stutters badly. Around town day to day driving the car acts fine.

Link to log
https://datazap.me/u/brockott/202111...og=0&data=4-20

A bit about the car. It’s a n55 dct, reman engine with ~1000 miles, PS2, dorch engineering HPFP, new coils, new plugs, stock injectors and LPFP (assume original). It running a tune from wedge.

Any suggestions on what to check? Reading forums people mention EKP or LPFP. Anyway I can test/check these without just replacing the parts? Also do the fuel filters get clogged?

Any help is really appreciated.

[Aceway]

Did you check the injector lines? My cylinder 6 injector line was leaking at the connection and it would misfire every time I went to the canyons for some spirited driving. Put teflon tape on the threads while I waited for a new pipe.

[Baileyboo]

Originally Posted by Aceway

Did you check the injector lines? My cylinder 6 injector line was leaking at the connection and it would misfire every time I went to the canyons for some spirited driving. Put teflon tape on the threads while I waited for a new pipe.

I’ll check them in more detail but I did look around the hpfp, lines and injectors quickly and didn’t see anything off or smell raw fuel.

[Baileyboo]

Checked and nothing appears to be leaking. Ended up getting a replacement ekp, didn't help and the issues still present.

Ordered a lpfp and new regulator/filter. At this point just throwing parts at the issue.

Fingers crossed it's one of those parts but still open to suggestions on things to check

[ferocity02]

What fuel and boost? Highly possible the stock LPFP can't keep up.

[Baileyboo]

Pump 92 for fuel and target boost at ~17psi. I’m also getting some cold start stalls so something just isn’t working as it should. New oem lpfp and filter/regulator arrive Saturday. Should know by Friday morning if it’s either of those

[Baileyboo]

I replaced the LPFP and the filter/regulator and it didn’t help the situation.
Current issue, the fuel rail pressure is dropping from ~2800 down to ~400 after a few seconds of WOT. The log still shows that the required rail pressure to 2800 after the actual pressure crashes. The car stumbles and throws the codes for Misfire fuel injection deactivation for cylinders 2, 3 & 4 and also misfire detected 2, 3 & 4. It seems to be consistent with these cylinders.

All the components of the fuel system are new except for the injectors. But it doesn’t make sense that the injectors are failing since they are capable of hitting the fuel pressure target for a few seconds.

[ferocity02]

Originally Posted by brockott

Pump 92 for fuel and target boost at ~17psi. I’m also getting some cold start stalls so something just isn’t working as it should. New oem lpfp and filter/regulator arrive Saturday. Should know by Friday morning if it’s either of those

I was suggesting that the stock LPFP may not be keeping up, as in you need a stage 2 pump.

What did Dorch say?

[Baileyboo]

Reached out to Dorch and they mentioned the rail pressure dropping off at an extremely low load ~3k rpm and about 10psi. They said usually this is a lpfp or ekp issue but we’re stumped since both those components had been addressed. I have my tune through wedge and they only mentioned needing to upgrade the hpfp in the later n55 135i and the stock lpfp would be fine for non ethanol blends for the ps2.

[Baileyboo]

I could have gotten a bad ekp or fuel pump but the symptoms presenting in the same way seems suspicious. They mentioned there could be an issue with their hpfp but it’s unlikely. I have the stock unit and might swap that back in this weekend and see just to rule that out.

Below is an updated log after the fuel pump and regulator.

https://datazap.me/u/brockott/202112...og=0&data=4-20

Also shout out to dorch. Emailed their generic custom support form and heard back within an hour with detailed feedback. Those guys are great.

[Baileyboo]

A little follow up. I think it maybe related to my custom wedge performance tune. I flashed to a stock tune and there are no issues with the car WOT any gear or rpm.

Reached out to Wedge and waiting for a response, I’m pretty frustrated with Steven at this point. I know they’re busy but I generally get one word responses about 3day to a week later. Based on those one word answers I’ve also replaced $1k worth of likely good parts chasing down this problem that might be tuning related.


Also Dorch mentioned that a stock lpfp is more than enough to provide fuel (pump gas) to a ps2.

Stock tune logs, the stock tune doesn’t require as high of rail pressure/load as the custom tune but it’s solid with no drop.

https://datazap.me/u/brockott/202112...og=0&data=4-20

https://datazap.me/u/brockott/202112...ata=4-18-19-20




Edit:The issue resolved itself a few weeks later. Not really sure the culprit but have been driving it daily with now issue since middle of Jan with rock solid rail pressure.

[saabstory]

Hi, I'm having the exact same issue except towards the upper rpm range and rail pressure drops to 1400ish causing a misfire with no codes. I have a 2013, which was running fine on the wedge tune until suddenly this issue occurred.

I took apart the LPFP assembly to check for burst lines and also jumped the secondary LPFP, which works, but still dipping too low.

Do you have any suspicion as to what might have been causing the issue?? I'm leaning towards mine being either bad gas or an intermittent faulty fuel pressure regulator. I don't believe mine is the HPFP because I have no other symptoms, and, the problem started randomly.