TrueTexan

Hi. Newby here. Bought a used 2011 528i in spring of 2023. Very nice interior, smooth and comfortable ride. A little background before moving on to the current problem... One summer night, got a drivetrain malfunction warning. Engine sputtered and died. Engine would turn over, and occasionally fire, but would not run. Unplugged MAF, and tried again and found the engine would run without it. Later I found out that it had low fuel pressure, around 32 PSI. So somehow unplugging the MAF tricked the DME to run the engine on low fuel pressure, I guess. Found a blown out O-Ring on the fuel pressure regulator inside the fuel tank, next to the fuel pump. I stuffed the O-Ring back into place just as a test, and started the engine. The fuel pressure then went up to about 90 PSI. Since this seemed too high, I figured the regulator was definitely bad, and bought a new fuel pump/regulator assembly and installed. Fuel pressure now bumps up to 74 PSI when turning ignition power on. However, while the engine is running, the fuel pressure stays around 80 PSI. Is this too high? Reason I ask... my EKPS module now overheats on a warm day and shuts down after driving about 15 minutes. Could it be running the fuel pump voltage from the module's output is too high all the time, overheating the module? Is there a way to configure the EKPS to reduce voltage output to the fuel pump in order to reduce fuel pressure down to 72 PSI while idling? Any ideas? Thanks in advance

seanjordan20

Short answer is no you can't configure the EKPS. The DME sends information to the EKPS then EKPS translate that data from the CAN bus to PWM output voltage for the electric pump.

The LPFP pressure is monitored by the pressure sensor and is only controlled by demand. I would ask first what brand pump assembly did you install in the tank? Also did you change out the MAF and if not is it the original?

TrueTexan

Thanks for the reply. I replaced the MAF on the following day after it died, and reset faults in ISTA+. However, all symptoms behaved exactly the same. Engine would sputter and die with new MAF, just like the old one. So I looked elsewhere. Took a long time to realize the fuel pressure was low. I ordered a cheap fuel pump assembly from Amazon and installed it. Thought it fixed the issue until warmer weather arrived. I got no indication from the KOMBI that anything else was bad. You mentioned the fuel pressure sensor might be bad. I'd consider replacing it, but can't locate it on the car. On other engines, it is located on the back end of the fuel rail, but can't find it on the N52. Any pointers? Thanks.

seanjordan20

One thing you'll learn about BMW aftermarket parts that makes the car run does not agree with the car. I would advise you to purchase a Pierburg (p/n 702701590) off rockauto. It is the OEM brand. Also if the MAF is not a VDO switch it back to the original.

The sensor sits under the throttle body. You should see a right next to the starter.

TrueTexan

OK. Thanks for the info. I'll look at ordering another fuel pump.
Meanwhile, I just measured the voltage coming out of the EKPM3 to the fuel pump. It starts around 12.5 VDC and within 10 seconds of idling, it increases to about 13.5 VDC and the fuel pressure increases to 80 PSI. Not only is the EKPM3 module getting hot to the touch, but also the fuel pump wiring is getting too hot, as well. Just seems strange that it would be outputting that much voltage when the pressure is already too high. Can definitely re-install the original MAF sensor to see if it makes a difference.

Next question: Wondering if this points to an issue with the fuel pressure sensor. Any idea whether the fuel pressure sensor is an on/off switch, or does it provide variable pressure feedback to the DME? Many thanks.

seanjordan20

The sensor has a strain gauge which is deformed by the adjacent pressure. The changes in resistance are detected and evaluated and then the measured voltage is included as a value in the pump. Short answer no it's not an on/off sensor.

The EKPS voltage supply range is 6-16v so it's within range. I can't give an educated guess because I have seen stranger things while using aftermarket parts. An owner a couple months on this forum had a similar situation and replaced the pump twice. He couldn't figure out what the issue was. We recommended OEM and once it was installed problem was solved. I can't remember exactly all of his problems put I do know he was having pressure issues. I've worked on BMWs long enough to know not to troubleshoot issues when aftermarket parts are installed. It runs you in circles.

TrueTexan

Before I pull the trigger on buying the OEM replacement low pressure fuel pump, am running some more tests on it first to rule some things out. I noticed on ISTA+ software, the EKPS has 3 ECU functions that can be triggered manually:
1) "Actuation of electric fuel pump - pressure regulation"
2) "Actuation of electric fuel pump (120 l/h)"
3) "Actuation of electric fuel pump (60 l/h)"
I'm assuming l/h means liters per hour.
When I trigger the pump with engine off, (battery at 12.5 VDC) the PKM3 outputs a little above 11vdc (same voltage each time) to the low pressure fuel pump motor in all three modes.
When the engine is running, (15.1 VDC) the the PKM3 outputs about 13.3 VDC to the fuel pump motor. And again, the fuel rail pressure hits 80 PSI each time.
I question whether the EKPM3 module is behaving properly or not. Seems to me like the 120 liters/hour test should output more voltage to the fuel pump than the 60 liters/hour test. Also, it would seem to me like the pressure regulation test should automatically and efficiently adjust the voltage output to the pump to maintain pressure, based on engine demand or fuel pressure sensor feedback.
I'm wondering if the DME learned adaptations might need to be reset if it ran on a bad fuel pump for a long time previously. Such as, could it have learned to adapt to a fuel pump that was slowly wearing out over the course of several months/years previously? Not sure how long these learned adaptations last before they resolve themselves.
Any thoughts on this?
Thanks

TrueTexan

I purchased a new EKPM3 module and installed it this evening. Confession time: it's a cheap knock-off version. But it's mainly because I couldn't justify spending the big money on something that I wasn't 100% sure was bad. Before starting the engine, I wanted to check the output voltage (to the low pressure fuel pump) to see if it was going to behave any differently than the module I removed. So I fired up the ISTA+ software and connected to the car. The software control unit tree showed the EKPS symbol in red, and said the ECU was non-responsive. However, I could trigger the fuel pump through a test function in the DME, and it worked. The module's output voltage was 9.5VDC and the fuel pump was quieter. Also, the fuel pressure was a steady 74 PSI at the fuel rail instead of 80 PSI. So I started the vehicle and let it warm up. The new EKPM3 module continued operating, outputting 9.5VDC at idle. The old module would have been outputting 13.3 VDC at this point. I expected the engine to lean-out and sputter if I revved it. However, the module increased the output voltage relative to engine RPM and kept up with the demand. So at an engine speed of around 3000 RPM, the EKPM3 module's output voltage increased to about 10.8 VDC. So I guess that even though the DME says the EKPS ECU is non-responsive, it still works. Makes me wonder if the DME sends a separate analog signal to the EKPM3 module to regulate the fuel pump speed based on demand, not relying on serial communication. So I took it out for a test-drive and it ran beautifully. When I got back home, the module temperature was still quite cool - like barely warm at all. Also the electrical connector and fuel pump wiring stayed cool, since the new EKPM3 module is no longer over-driving the fuel pump. I wouldn't say it is "fixed" necessarily since the DME can't communicate with it, but it seems to point out that the old EKPM3 module was definitely bad.