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Title: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: nubcake on November 01, 2015, 07:56:00 AM RS6 C5, highly custom, with 550cc injectors and 3 bar FPR.
Lots of DTCs were hidden with CLA***, I'm reverting those and trying to fix the causes instead of hiding problems. I guess this DTC comes from the FPR being lower spec than stock (4 bar), but how does ECU know it? There's no fuel pressure sensor as far as I can tell. So, it must calculate it somehow. Meaning, that some constant or table can be altered to make it happy again. Any ideas? :) Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: ddillenger on November 01, 2015, 12:35:34 PM RS6 C5, highly custom, with 550cc injectors and 3 bar FPR. Lots of DTCs were hidden with CLA***, I'm reverting those and trying to fix the causes instead of hiding problems. I guess this DTC comes from the FPR being lower spec than stock (4 bar), but how does ECU know it? There's no fuel pressure sensor as far as I can tell. So, it must calculate it somehow. Meaning, that some constant or table can be altered to make it happy again. Any ideas? :) Is it still using the twin pump setup? Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: nubcake on November 01, 2015, 03:21:44 PM Yea, but fuel pump controller is bypassed. I had assumed that it might be related to this as well - will surely check this.
But, regardless, I think that this DTC can appear even with completely functioning fuel pump controller, when FPR is misbehaving. The question remains - how does ECU know this? :) Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: MoparFreak69 on November 04, 2015, 08:32:05 PM The ECU calculates fuel pressure based on actual injector on time vs what it should be based on injector offset voltages. It can tell fuel pressure is low if it has to fire the injectors longer than calculated to maintain afrs.
Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: ddillenger on November 04, 2015, 11:40:06 PM The ECU calculates fuel pressure based on actual injector on time vs what it should be based on injector offset voltages. It can tell fuel pressure is low if it has to fire the injectors longer than calculated to maintain afrs. Helluva trick on a narrowband car. Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: nubcake on April 06, 2016, 09:26:36 AM I guess, I'll give an update to this.
Thanks to the thread on DTC logic (http://nefariousmotorsports.com/forum/index.php?topic=10018.0) and error classes (http://nefariousmotorsports.com/forum/index.php?topic=567.0). I did some digging through code to find where and how this DTC is set. Found some function that is unique to RS6, so I can't really cross-reference it with other "defined" software and name vars/consts properly, but apparently it is responsible for controlling the fuel flow. It also can set P1063 and P1020 DTCs. It interfaces with other functions via few RAM vars, and those are mostly used by EKP ("elektrische Kraftstoffpumpe") routines. I did not invest enough time into figuring out the complete logic of this process, but apparently ECU checks back on fuel pump status reported by the fuel controller and limits the load via LDRLMX (http://nefariousmotorsports.com/forum/index.php?topic=8622.msg77002) if something's wrong. It also sets P1065 if the signal is missing completely. Also, for shits and giggles, I reverted to the 4 bar FPR - and surely enough, the DTC is still there. It also reappears almost instantly on idle after clearing it. So, after all, dd was right - it seems that it's the "missing fuel controller" that produces this DTC. Title: Re: P1065 DTC - how does ECU know? (Fuel Pressure Regulation:Regulation Discrepancy) Post by: NOTORIOUS VR on April 06, 2016, 11:33:37 AM Helluva trick on a narrowband car. Agreed... But them pesky German engineers... they'll find a way lol |