[redz06]

Over the past 5 months, my 2008 335i sedan will occasionally die. It has only occurred from idle condition. The tach reading just goes from say 650 rpm to zero. Hitting the starter button, the engine starts normally with no hesitation. If I am in a traffic jam the engine dying may occur several times in succession -- maybe every minute or so. Other than this occasional dying, the car runs very normally, even energetically.

My car has 97k miles on it, with new sparkplugs and filters about 20k miles ago. Other maintenance has been normal. The car had the HPFT replaced about 30k miles ago.

Two other episodes I should report: (1) About 4 months ago, I had the car on a road course, doing some instruction with my granddaughter. After a couple of sessions, I got the half engine warning and brought the car into the pits to determine what was going on. I borrowed a OBDII reader and erased the code and the car has run normally ever since. But not on the track since then. (2) A week ago I was driving the car and the acceleration was less than normal. It was as if the turbocharger was not allowed to boost the intake air pressure. It happens that the OBDII reader was in the car, so I hooked it up and found a code had been lodged. I erased the code and my boost returned, along with normal driving (other than occasionally dying because the idle RPM could not be maintained. Something is not right and I would appreciate input, as whatever is decided will determine where I take my car to be repaired.

Just for clarification, my BMW is stock and has the original factory tune. The only non-stock piece is the pipe between the intercooler and the throttle body.

[wrevilo]

Reading codes is really going to help narrow down issues. I'd advise that as a first step.

[oVeRdOsE.]

scan it.

on N55 its often the valvetronic actuator that does this behavior.

very common, and appears around 100k miles.

It will code, so scan and you'll see if it's the case.


If this is the issue, you can buy a little bit of time by running a relearn on ISTA. If it completes the 450 cycle no stall, you'll be fine for few more miles, until you replace it

[redz06]

I scanned it and it showed a pending code P15DF whatever that means. No other codes were stored or pending. I was able to erase that code.

If I remember correctly, that is the same pending code that was lodged when the engine acted like there was no boost.

[redz06]

Originally Posted by oVeRdOsE.

scan it.

on N55 its often the valvetronic actuator that does this behavior.

very common, and appears around 100k miles.

It will code, so scan and you'll see if it's the case.


If this is the issue, you can buy a little bit of time by running a relearn on ISTA. If it completes the 450 cycle no stall, you'll be fine for few more miles, until you replace it

I scanned it and it showed a pending code P15DF whatever that means. No other codes were stored or pending. I was able to erase that code.

If I remember correctly, that is the same pending code that was lodged when the engine acted like there was no boost.

[fastboatster]

If you have a 2008 335i then you have an n54, not n55. Need to scan it with Inpa or ISTA to get bmw specific codes.

[redz06]

Originally Posted by redz06

Over the past 5 months, my 2008 335i sedan will occasionally die. It has only occurred from idle condition. The tach reading just goes from say 650 rpm to zero. Hitting the starter button, the engine starts normally with no hesitation. If I am in a traffic jam the engine dying may occur several times in succession -- maybe every minute or so. Other than this occasional dying, the car runs very normally, even energetically.

My car has 97k miles on it, with new sparkplugs and filters about 20k miles ago. Other maintenance has been normal. The car had the HPFT replaced about 30k miles ago.

Two other episodes I should report: (1) About 4 months ago, I had the car on a road course, doing some instruction with my granddaughter. After a couple of sessions, I got the half engine warning and brought the car into the pits to determine what was going on. I borrowed a OBDII reader and erased the code and the car has run normally ever since. But not on the track since then. (2) A week ago I was driving the car and the acceleration was less than normal. It was as if the turbocharger was not allowed to boost the intake air pressure. It happens that the OBDII reader was in the car, so I hooked it up and found a code had been lodged. I erased the code and my boost returned, along with normal driving (other than occasionally dying because the idle RPM could not be maintained. Something is not right and I would appreciate input, as whatever is decided will determine where I take my car to be repaired.

Just for clarification, my BMW is stock and has the original factory tune. The only non-stock piece is the pipe between the intercooler and the throttle body.

My fault, my 335i sedan is a 2011 model, not a 2008. It does certainly have the N55 engine it was borne with. It is a European delivery, US spec car, built in the Munich factory and I have owned it from new. After the BMW warranty had expired, the HPFP did as well, so this was replaced about 30k miles ago. I understand that the fuel filter is in the fuel tank, so this has never been replaced, despite the 97k miles on the clock. Other parts which have been replaced are the water pump, belts and pulleys, and charge pipe. The tune is OEM stock.

As I said before, the BMW fault code was P15DF.

[fastboatster]

yeah, can be low pressure fuel pump and/or filter/low pressure regulator. or hpfp might be done again, these n54-style hpfps on early n55s are not that reliable. I'd start with in-tank filter/low pressure regulator before going to the hpfp

[gbalthrop]

Originally Posted by redz06

Over the past 5 months, my [2011] 335i [E90 N55] will occasionally die. It has only occurred from idle condition. The tach reading just goes from say 650 rpm to zero. Hitting the starter button, the engine starts normally with no hesitation. If I am in a traffic jam the engine dying may occur several times in succession -- maybe every minute or so. Other than this occasional dying, the car runs very normally, even energetically. My car has 97k miles on it, with new sparkplugs and filters about 20k miles ago. Other maintenance has been normal. The car had the HPFT replaced about 30k miles ago...

Originally Posted by redz06

I scanned it and it showed a pending code P15DF whatever that means. No other codes were stored or pending. I was able to erase that code. If I remember correctly, that is the same pending code that was lodged when the engine acted like there was no boost.

The "Court of DIAGNOSTICS" finds you Guilty of "Obstruction of Diagnosis" / "Destruction of EVIDENCE".

You describe an "Intermittent" issue that causes the engine to stall at idle, yet the engine Re-Starts, and then operates "normally, even energetically". An Intermittent Fault is usually electrical rather than mechanical, and is difficult to diagnose because you either (1) have to "Catch it in the Act", and be viewing the correct "Live Data" (or logging) when it happens, OR (2) READ the "Freeze Frame Data" associated with a Fault Code that MAY be saved with the code in DME Fault Memory.

There are FOUR (4) things you need to know about a Fault Code:
1) It does NOT tell you what part to REPLACE
It is a CLUE as to what system to Diagnose FURTHER;

2) You can LOOKUP the DEFINITION of the Code in "BMW Fault Code Lookup", and OFTEN (NOT always ;-) find suggestions of Tests you/your shop can do, to Diagnose the issue (see "Service Plan" in Fault Information Link). Here are Examples for YOUR Code, P15DF: Definition & Fault Info Link (View):
P15DF | 2BEE | High pressure fuel system, plausibility, cold start: Pressure too low | MEVD174K | Engine electronics
https://bmwfault.codes/XMLDiagView?d...EAOAAzADAANAA=

3) "Freeze Frame Data" is Saved in Fault Memory (at least in the DME) whenever a Fault Code is saved. That FF Data is a "Snapshot" of system conditions at the moment Fault Code was saved. Those "Conditions/ Parameters" are CLUES that are particularly helpful in diagnosing Intermittent issues, as they often show INPUTS to the DME that are "Out of Range" or Implausible, that CAUSED the Fault Code to be saved.

4) When you CLEAR/DELETE the Fault Code you also DELETE the FF Data associated with the Code.

So Clearing Fault Codes, WITHOUT RECORDING/ Saving the Fault Code & FF Data is "Destroying Evidence". INPA to the RESCUE:

ALL is NOT Lost if YOU/ Your Shop have INPA. For Several of the Modules in your vehicle, such as the DME (Engine Module), EKPS (Fuel Pump Module) & EGS, the "History Memory" or "HistorienSpeicher" continues to hold a record of the last 10 Fault Codes Saved in Fault Memory, and FF Data (including mileage/km when saved) for LAST 3 instances of that Fault. LOTS of "Evidence" still present in DME, IF you can read it!

In YOUR case, the Fault Code & Symptoms you describe suggest an intermittent fault related to Fuel Rail Pressure LESS than the Setpoint or Target pressure ("Sollwert") the DME is requesting. That Code does NOT mean there is an ACTUAL issue with rail pressure, as the DME only compares the Rail Pressure Sensor SIGNAL it receives (via wiring & connectors) to the "Target" value requested. ALWAYS check wiring & connectors BEFORE condemning/ replacing/ THROWING PART$.

I'm NOT familiar with N55 & HPFP, but my understanding is that there is a "Rail Pressure Sensor", and also a "Volume Control Valve" on the HPFP that is "Triggered" by the DME to change HPFP Output and actual rail pressure. Make sure to check BOTH parts of the circuit of High Pressure Fuel System.

Note that there is also "History Memory" in the EKPS Module Fault Memory. There MAY be an issue with actual Fuel Delivery by the Low Pressure Pump. So you want to look for any Fault Codes in EKPS History Memory, the mileage at which any occurred, and consider if LPFP function is related to your issue.

Live Data:
1) If the Engine Stall at idle occurs within several minutes of idle at a certain engine temperature, you can OBSERVE the Values for:
a) Low Pressure Fuel System Pressure (~ 72 PSIG/ 87 bar) &
b) Rail Pressure or HPFP Pressure.

2) Simply observing that Live Data at the moment of Stall should offer Clues as to what is happening. You want to know IF Low Pressure Value drops BEFORE stall, or if THAT remains in range, and ONLY the Rail Pressure Value drops.

AFTER observing Live Data during Stall, you need to TEST components & wiring to determine if there is an ACTUAL pressure drop, or ONLY a Signal value drop. Do you have a Component Fault, or a wiring/ electrical Fault?

By NOW, you should understand why MANY folks in a shop are good at turning a wrench, but Diagnostics: NOT so much. It takes a LOT of Knowledge of: (a) HOW systems work, (b) wiring diagrams, (c) Diagnostic Software capabilities & (d) HOW the codes are Set (perhaps the hardest info to obtain), as well as the Diagnostic Equipment itself, to be able to BEGIN. Then it takes time & ability to Evaluate the Clues. Easy to see why most shops, in business to make money, Throw Part$. The more YOU know about "what is possible" using Diagnostic Software, such as INPA or ISTA, the better your chances of getting a good RESULT from a $hop.

Please let us know what you find, and/or if you have specific questions. When you post back, please provide Last-7 Characters of your VIN, so we can provide correct wiring & component diagrams for YOUR vehicle.
George

[fastboatster]

Good points, I’ll have to add that you can’t log lpfp pressure on the early n55s, there’s no low pressure fuel line pressure sensors, there’s sensor in the high pressure circuit only. So will have to use a pressure gauge to measure the pressure in the lpfp circuit and drive around with that, may not be feasible.

[gbalthrop]

Originally Posted by fastboatster

... there’s no low pressure fuel line pressure sensors, there’s sensor in the high pressure circuit only...

Having NO N55 to test, I ONLY go by the 9/2010 build N55 ISTA diagram attached, showing B6125a Sensor.
George

[fastboatster]

I see, mine is 06/2011, it doesn't have it

[redz06]

Originally Posted by gbalthrop

The "Court of DIAGNOSTICS" finds you Guilty of "Obstruction of Diagnosis" / "Destruction of EVIDENCE".

You describe an "Intermittent" issue that causes the engine to stall at idle, yet the engine Re-Starts, and then operates "normally, even energetically". An Intermittent Fault is usually electrical rather than mechanical, and is difficult to diagnose because you either (1) have to "Catch it in the Act", and be viewing the correct "Live Data" (or logging) when it happens, OR (2) READ the "Freeze Frame Data" associated with a Fault Code that MAY be saved with the code in DME Fault Memory.

There are FOUR (4) things you need to know about a Fault Code:
1) It does NOT tell you what part to REPLACE
It is a CLUE as to what system to Diagnose FURTHER;

2) You can LOOKUP the DEFINITION of the Code in "BMW Fault Code Lookup", and OFTEN (NOT always ;-) find suggestions of Tests you/your shop can do, to Diagnose the issue (see "Service Plan" in Fault Information Link). Here are Examples for YOUR Code, P15DF: Definition & Fault Info Link (View):
P15DF | 2BEE | High pressure fuel system, plausibility, cold start: Pressure too low | MEVD174K | Engine electronics
https://bmwfault.codes/XMLDiagView?d...EAOAAzADAANAA=

3) "Freeze Frame Data" is Saved in Fault Memory (at least in the DME) whenever a Fault Code is saved. That FF Data is a "Snapshot" of system conditions at the moment Fault Code was saved. Those "Conditions/ Parameters" are CLUES that are particularly helpful in diagnosing Intermittent issues, as they often show INPUTS to the DME that are "Out of Range" or Implausible, that CAUSED the Fault Code to be saved.

4) When you CLEAR/DELETE the Fault Code you also DELETE the FF Data associated with the Code.

So Clearing Fault Codes, WITHOUT RECORDING/ Saving the Fault Code & FF Data is "Destroying Evidence". INPA to the RESCUE:

ALL is NOT Lost if YOU/ Your Shop have INPA. For Several of the Modules in your vehicle, such as the DME (Engine Module), EKPS (Fuel Pump Module) & EGS, the "History Memory" or "HistorienSpeicher" continues to hold a record of the last 10 Fault Codes Saved in Fault Memory, and FF Data (including mileage/km when saved) for LAST 3 instances of that Fault. LOTS of "Evidence" still present in DME, IF you can read it!

In YOUR case, the Fault Code & Symptoms you describe suggest an intermittent fault related to Fuel Rail Pressure LESS than the Setpoint or Target pressure ("Sollwert") the DME is requesting. That Code does NOT mean there is an ACTUAL issue with rail pressure, as the DME only compares the Rail Pressure Sensor SIGNAL it receives (via wiring & connectors) to the "Target" value requested. ALWAYS check wiring & connectors BEFORE condemning/ replacing/ THROWING PART$.

I'm NOT familiar with N55 & HPFP, but my understanding is that there is a "Rail Pressure Sensor", and also a "Volume Control Valve" on the HPFP that is "Triggered" by the DME to change HPFP Output and actual rail pressure. Make sure to check BOTH parts of the circuit of High Pressure Fuel System.

Note that there is also "History Memory" in the EKPS Module Fault Memory. There MAY be an issue with actual Fuel Delivery by the Low Pressure Pump. So you want to look for any Fault Codes in EKPS History Memory, the mileage at which any occurred, and consider if LPFP function is related to your issue.

Live Data:
1) If the Engine Stall at idle occurs within several minutes of idle at a certain engine temperature, you can OBSERVE the Values for:
a) Low Pressure Fuel System Pressure (~ 72 PSIG/ 87 bar) &
b) Rail Pressure or HPFP Pressure.

2) Simply observing that Live Data at the moment of Stall should offer Clues as to what is happening. You want to know IF Low Pressure Value drops BEFORE stall, or if THAT remains in range, and ONLY the Rail Pressure Value drops.

AFTER observing Live Data during Stall, you need to TEST components & wiring to determine if there is an ACTUAL pressure drop, or ONLY a Signal value drop. Do you have a Component Fault, or a wiring/ electrical Fault?

By NOW, you should understand why MANY folks in a shop are good at turning a wrench, but Diagnostics: NOT so much. It takes a LOT of Knowledge of: (a) HOW systems work, (b) wiring diagrams, (c) Diagnostic Software capabilities & (d) HOW the codes are Set (perhaps the hardest info to obtain), as well as the Diagnostic Equipment itself, to be able to BEGIN. Then it takes time & ability to Evaluate the Clues. Easy to see why most shops, in business to make money, Throw Part$. The more YOU know about "what is possible" using Diagnostic Software, such as INPA or ISTA, the better your chances of getting a good RESULT from a $hop.

Please let us know what you find, and/or if you have specific questions. When you post back, please provide Last-7 Characters of your VIN, so we can provide correct wiring & component diagrams for YOUR vehicle.
George

Thank You George. Guilty as Charged. The last 7 characters of my VIN are E758738. It is a Eurodelivery US spec car. I will inquire whether my indy BMW shop has INPA or ISTA. The BMW dealerships in my area have failed to earn my confidence. Whatever fault is causing my issue, it is unpredictable and you know how frustrating it is to take a car in for service and then the shop is unable to reproduce the issue. With my car, months may go by without an issue. I can tell you that the issue only occurs from idle, it occurs at normal operating conditions, and is entirely not an issue on restart.

Keeping my OBDII reader connected to the port for months at a time, hoping for the engine to die is a problem which I am not sure how to resolve. Likewise, putting my car in a shop such that the owner can drive it for months to get the problem to replicate itself is also a problem. Hopefully, INPA/ISTA can resolve the problem such that it can be solved.