elias 230 Report post Posted April 11, 2022 Hello, I am having a bit of trouble with my car atm, its a FBO n54 135i on MHD stage 2+. Took it for a good drive the other day, giving it some abuse on some windy roads, with a lot of traction control stepping in as rear tires are pretty bad. After the twisty road, I go up a hill to pass someone (in a passing lane) and car starts shaking, at first I though it was traction control again because I accelerated quite quick but it shook more and more and the check engine light started flashing, so I pulled over, turned car off, scanned the codes and got: 29CC DME: combustion misfires several cylinders 29CD DME: combustion misfires cylinder 1 29CE DME: combustion misfires cylinder 2 29CF DME: combustion misfires cylinder 3 I cleared the code, car ran fine at idle, and gently drove it home, ran relatively smooth no real issues, when I did try a bit of acceleration it got rough so I stopped before it misfired too bad. Got home, swapped coils and plugs from bank 1 to bank 2 and took it for test drive, all good at low rpm (waiting for engine to warm up) did one small pull as soon as it hit a bit of boost breaks up again and misfires really violently. Pulled over scanned codes again: 29DC Injector cutout Cleared code, started car and gave it one more small acceleration while doing MHD data log (stopped acceleration before it misfired bad enough to go into limp mode) which showed the following: https://datazap.me/u/hlf529/injector-cutout?log=0&data=3-22 To me it looks like a fuel issue, rail pressure drops far too low and low pressure sensor fluctuates a lot, im leaning towards being a low pressure fuel pump issue but want to be sure before I buy one and replace it. Note: Coil packs/ plugs are all only a few months old (Delphi coils/ngk one step colder plugs) Any idea/help/advice would be much appreciated Quote Share this post Link to post Share on other sites
NZ00Z3 186 Report post Posted April 11, 2022 Yes, the fuel pressure is too low. Confirmed by the: Fuel Pressure low sensor Both Short Term fuel trims. 1 Quote Share this post Link to post Share on other sites
Gaz 1040 Report post Posted April 11, 2022 Showing signs of high pressure fuel pump failure Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 11, 2022 51 minutes ago, NZ00Z3 said: Yes, the fuel pressure is too low. Confirmed by the: Fuel Pressure low sensor Both Short Term fuel trims. right that makes sense, now my issue is finding the cause, LPFP, HPFP, low pressure sensor? I might be wrong but I believe the HPFP is fine, before the Low pressure sensor reading drops, the HPFP builds nice up to 1400psi with no issues, then Low pressure drops down, and the rail pressure follows, dropping really low. Looks like LPFP to me but keen to get some other opinions before I buy one Quote Share this post Link to post Share on other sites
jon dee 500 Report post Posted April 11, 2022 (edited) HPFP don't look well... on that second little blip it just runs and hides Cheers... Edited April 11, 2022 by jon dee Afterburner kicked in YO !!! Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 11, 2022 appreciate the help! So looks like either HPFP or LPFP or both are the culprit, got a second hand LPFP that I picked up for a great price coming now to eliminate that issue before o drop $$ on HPFP, will see how it goes cheers Quote Share this post Link to post Share on other sites
jon dee 500 Report post Posted April 11, 2022 Doesn't look as if there is much wrong with your LPFP. The fluctuations are probably due to the pump control trying to keep up with corrections on a rapidly changing demand. Here is one of my N54 logs for comparison... If you can visualize a RMS smoothing of the output it would be staying pretty close to the target pressure. Cheers... 1 Quote Share this post Link to post Share on other sites
KwS 2372 Report post Posted April 11, 2022 (edited) It was real obvious when my LPFP was packing a sad, there was a direct correlation in the HP rail pressure dropping when the low pressure dropped, i dont see that in your logs. I'd say the HPFP is more likely. Your rail pressure drops to just over 100psi at one point, whilst the low pressure side just keep trying to feed more pressure in, getting to almost 100psi on the low pressure side alone, you wouldnt see that if the LPFP was on its way out. Edited April 11, 2022 by KwS Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 11, 2022 right I see that makes a lot of sense, time to start looking for a high pressure fuel pump then. Only reason I though it was the low pressure pump was because the low pressure sensor reading dropped quite low which Im not sure why it would do that. Either way, I shall look for a high pressure fuel pump, I paid $60 for a known good OEM LPFP, thought it would be a cheap way of making sure im not spending money on a HPFP when it might not be necessary but I see what you're saying and agree it is rather likely to be a HPFP issue, really appreciate the help with this! Quote Share this post Link to post Share on other sites
jon dee 500 Report post Posted April 11, 2022 It almost looks like the pump speed controller has given up controlling, and the pump is running in some kind of limp home mode. If the controller was working it would not allow the huge overshoot you see when you come off the gas. Here is a detailed description of how the HPFP works (God bless Google and all who sail in her). Since you lost pressure suddenly I think it is worth checking to see you did not shake the plug loose on the Fuel Supply Control Valve. https://www.1addicts.com/forums/showpost.php?s=24ab971231a46b65ddcf06199447cdbe&p=5752164&postcount=9 Cheers... Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 12, 2022 Thanks for the link, good read, lots of good information in there. Had a look around the HPFP, all the connections look good, no loose plugs, all the plugs on the junction box under the intake manifold look good too, no damaged wires etc. So seems like it could be HPFP itself Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 13, 2022 replaced the LPFP with a known good low km oem one, still same issue, fuel pressure (both rail pressure and low pressure sensor reading) drops under load and car loses power and stumbles/misfires. Would failing HPFP cause the low pressure reading to fluctuate? or is it more likely a bad low pressure sensor or EKP? new log after new LPFP, seems like low pressure drops before rail pressure so not sure its the HPFP's fault https://datazap.me/u/hlf529/still-sh*t?log=0&data=10-19-24 Quote Share this post Link to post Share on other sites
F10er 62 Report post Posted April 13, 2022 Definitely sounds like hpfp. Do you know anybody that has ISTA? There's a test that it can do on the hpfp that determines if it's any good or not. And I'm almost certain there's also a test that you can run which tests the low pressure system as well. Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 13, 2022 ok sweet I mean it makes sense, being one of the most common parts on these cars to fail an I think im still on my original one at 132,000kms. Will try see if I can maybe get access to ISTA seems like a useful tool to have! Quote Share this post Link to post Share on other sites
F10er 62 Report post Posted April 13, 2022 GUIDE TO ISTA+.pdf Quote Share this post Link to post Share on other sites
jon dee 500 Report post Posted April 14, 2022 (edited) Seeing how the DME controls the Fuel Supply Control Valve, it surprises me that it doesn't throw a HPFP related trouble code Anyways here is the last part of your log. For the life of me I can't figure out where the fuel is coming from ?? The rail pressure is on the floor, boost is going up but the trims are taking out fuel and the AFR's are not far from where they should be... that's fcuking crazy !!! Cheers... Edited April 14, 2022 by jon dee Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 21, 2022 all sorted now, fuel pump failed completely on my way to a workshop, rail pressure dropped below 100psi and didn't recover. Replaced HPFP and no issues now, data logs must have looked odd because the pump hadn't failed entirely and the low pressure side was trying to compensate. Appreciate the help with this issue cheers 2 Quote Share this post Link to post Share on other sites
jon dee 500 Report post Posted April 21, 2022 (edited) Thanks for the update And you can be happy that your fuel system is good to go for another 100,000 km Cheers... Edited April 21, 2022 by jon dee Quote Share this post Link to post Share on other sites
elias 230 Report post Posted April 21, 2022 No worries, nothing quite as annoying as looking through old forum posts that describe the same issue and never seeing what the solution was. Yeah hopefully it'll be ok for a while, until I decide to bolt bigger turbos onto it at some point haha Quote Share this post Link to post Share on other sites
