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Long cranks on cold start. Low rail pressure. Ideas?
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12-26-2018, 01:42 PM | #1 |
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Long cranks on cold start. Low rail pressure. Ideas?
Hi guys,
Since I have owned my car I have been chasing down the cause of the long crank cold starts that I get every time the car sits for more than a few hours. For the longest time I thought it was due to my HPFP, but once I replaced that, the long cranks were still occurring. Over the past few months since replacing my HPFP I feel as if they have been happening more frequently, so I decided to log a few of them to see whats going on. Here are 3 long crank cold starts: https://datazap.me/u/geirsenk/long-c...og=1&data=3-13 https://datazap.me/u/geirsenk/long-c...og=2&data=3-13 https://datazap.me/u/geirsenk/long-c...og=0&data=3-13 And for a baseline, heres a log of when the car fired up pretty normally (still cold). https://datazap.me/u/geirsenk/more-c...=2&data=0-3-13 The biggest contributing factor from what I can see has to be the rail pressure before cranking over. In all of the logs it is at 18 PSI, which I know for a fact is low. Considering I have a new motor with new injectors, new HPFP, and the starter/battery are fully healthy, I have narrowed it down to the fueling before the motor. This leaves me with either the LPFP or the fuel regulator. Either the LPFP isn't priming as much as it should, or the lines are losing a lot of pressure while sitting. My LPFP sounds fine when it primes and doesn't give me any codes or drivability issues either. Anyone have any ideas as to what to look for or test? I really want to avoid blindly replacing any parts at this point. Cheers.
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12-26-2018, 04:49 PM | #2 |
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Was the car recently programmed? As you stated you can hear the lpfp priming but that doesn't necessarily mean it's pushing enough fuel to the front. Also have a look at the ekps control unit. This Module controls the lpfp. Also how many miles on the vehicle and mods?
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12-26-2018, 10:12 PM | #3 |
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Long cranks on cold start. Low rail pressure. Ideas?
When I had long cranks, the dealer replaced both the hpfp and the high pressure sensor (part number 13537620946). Maybe try replacing that as well?
https://www.fcpeuro.com/products/bmw...re-13537620946 https://www.getbmwparts.com/oem-part...re-13537620946
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12-27-2018, 08:47 AM | #4 |
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There is a procedure in ISTA to keep running ur low pressure fuel pump for longer times.
I would do that and check ur rail pressure with car off. See how it changes. Whether it builds up then drops etc.. Then u know something is ot holding pressure. If it does not change much ur fuel pressure sensor could be bad like the above post mentioned. It could be good for high pressures but not sensitive enough for low pressures.. |
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12-27-2018, 08:59 AM | #5 | |||
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12-28-2018, 05:55 AM | #6 |
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That function is part of a test module. If you wanted to run the low pressure pump constantly you could just provide direct fused power to the pump under the seat.
The proper way to test the low pressure system is to also check the plausibility of the sensor reading vs a known good gauge that is teed into the feed line. Based on those logs I'd say your pressure sensor is good because the data supports the symptoms you are experiencing. You should at least have 4-5bar in the rail, indicating the low pressure side is at least providing enough pressure. |
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12-28-2018, 09:37 AM | #7 | |
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12-30-2018, 03:09 PM | #8 |
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If you smell fuel while driving, I would check all of your fuel line connection points post hpfp. Probably a leak somewhere allowing air in the lines somewhere or even a leaky injector making it hard to build pressure upon startup.
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01-11-2019, 12:23 PM | #9 |
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I had long cranks for a while. Continuously got worse until the starter finally died on me. Could be your starter beginning to go. Might be your best case scenario as I had the car die and I was able to diagnose, source parts, and repair it all within a day with basic tools for less than $300.
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01-11-2019, 01:57 PM | #10 | ||
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01-11-2019, 01:59 PM | #11 |
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01-13-2019, 06:18 AM | #12 | |
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Stuck open injector would usually cause a rich miss, sooty/smoky exhaust and glowing cat if present. Have you been able to measure a voltage at the low pressure pump when it primes? |
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01-14-2019, 01:45 PM | #13 |
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This is going to be the next course of action when I get the chance. The LPFP sounds healthy when priming, but I plan on double checking the voltage to be sure.
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2011 335i N55/6MT/M-Sport
MHD Stage 2+, VRSF Downpipe, VRSF 7" FMIC, BMS Intake, BMS Chargepipe, Performance Exhaust Mod, F10 550i Clutch, BMS CDV, BMW Performance SSK, M3 Control Arms, ST Coilovers, Apex ARC-8 wheels, Michelin PS4S |
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01-14-2019, 02:00 PM | #14 |
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I hope you figure this out cause I'm pretty close to replacing my fuel pressure regulator for shits to see if it fixes the problem. It only seems to happen when it's near freezing, which makes me wonder if something is not quite sealing as well as it used to anymore.
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01-14-2019, 05:01 PM | #15 | |
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2011 335i N55/6MT/M-Sport
MHD Stage 2+, VRSF Downpipe, VRSF 7" FMIC, BMS Intake, BMS Chargepipe, Performance Exhaust Mod, F10 550i Clutch, BMS CDV, BMW Performance SSK, M3 Control Arms, ST Coilovers, Apex ARC-8 wheels, Michelin PS4S |
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03-20-2019, 08:41 AM | #16 |
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Let me know if that helps, Cold starts are a pain sometimes
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04-11-2019, 11:49 AM | #17 |
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Bumping for an update.
I finally got around to doing a full test of the fuel system. I Tee'd a fuel pressure gauge into the HPFP line and tracked the pressure compared to what the DME was commanding the LPFP to do through INPA. The pressure differences confirmed that my LPFP is working just fine, leaving the culprit to be the "fuel pressure regulator" or "fuel sending unit" (I have heard it called both) on the driver side of the fuel tank. From the research I have done, on 2011 N55 cars without the low pressure fuel sensor, this tends to be the fix if the HPFP has already been replaced and no other codes are present. From my understanding, the fuel pressure regulator monitors and sends fuel from the left side of the tank to the LPFP on the right side of the tank. https://www.fcpeuro.com/products/bmw...ft-16117163295 The part isn't too bad cost-wise, and the DIY is pretty simple. It should pretty much involve taking the rear seat out and pulling the unit out along with the fuel lines that run to the LPFP. I am currently waiting on the part to arrive and will check back once I install it.
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MHD Stage 2+, VRSF Downpipe, VRSF 7" FMIC, BMS Intake, BMS Chargepipe, Performance Exhaust Mod, F10 550i Clutch, BMS CDV, BMW Performance SSK, M3 Control Arms, ST Coilovers, Apex ARC-8 wheels, Michelin PS4S |
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04-22-2019, 06:11 PM | #19 | |
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04-23-2019, 11:17 AM | #20 | |
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04-23-2019, 05:36 PM | #21 | |
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I have been super busy as of recently with starting a new job, moving, and graduating college, so I haven't had any opportunity to do the regulator job yet. I read your other thread and saw that you decided to tackle it. I look forward to hearing your update if you end up doing it before me.
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2011 335i N55/6MT/M-Sport
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05-01-2019, 07:01 PM | #22 | |
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