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      08-09-2021, 04:48 AM   #1
bobbykolev
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Fuel rail pressure drop/// please help

Hi guys. I have strange issue with my 435.
I have very strange fuel pressure drop when i am on full throttle. Fuel drops for less than a second and then continues without a problem.
I have changed the fuel rail pressure sensor, upgraded the HPFP with b58 pump (not TU pump), new oem bosch spark plugs, new oem coils, i have cleaned the injectors and the rail itself. The guys who testes the injectors said that they are ok.
I am currently using a custom tune from a local tuner in my country. With the stock file the car have no issues at all.
I've imported the car from Canada to Bulgaria where i currently live. Could it be a ECU problem or i should change the fuel injectors with new one?
I really dont know what to do...
You can see on the graphic here. Red is fuel, green boost
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      08-09-2021, 05:15 AM   #2
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Quote:
Originally Posted by bobbykolev View Post
Hi guys. I have strange issue with my 435.
I have very strange fuel pressure drop when i am on full throttle. Fuel drops for less than a second and then continues without a problem.
I have changed the fuel rail pressure sensor, upgraded the HPFP with b58 pump (not TU pump), new oem bosch spark plugs, new oem coils, i have cleaned the injectors and the rail itself. The guys who testes the injectors said that they are ok.
I am currently using a custom tune from a local tuner in my country. With the stock file the car have no issues at all.
I've imported the car from Canada to Bulgaria where i currently live. Could it be a ECU problem or i should change the fuel injectors with new one?
I really dont know what to do...
You can see on the graphic here. Red is fuel, green boost
what fuel? what tuning software? can you post a log?

what mods on the car?
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      08-09-2021, 05:57 AM   #3
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Quote:
Originally Posted by Phantom10R View Post
what fuel? what tuning software? can you post a log?

what mods on the car?
I am running 100 RON. Mods - chargepipe, boostpipe, downpipe,carbon cold air intake, intercooler 6", Turbosmart BOV, M performance exhaust system, mosselmann sport oil thermostat.
I can only record live data, dont have datalogs.
As i said the tune is custom.
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      08-09-2021, 11:31 AM   #4
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The tune is custom but what is the tuning software? In other words what did you use to flash it?

In addition to the things you mentioned, it could be the LPFP.
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      08-09-2021, 03:19 PM   #5
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No issue with LPFP. 6.8 bar always, never dropped lower than normal.

He flashed it directly through ECU port. Didnt use OBD.
But what programme he uses, i have no idea...


Quote:
Originally Posted by thejeremyman9 View Post
The tune is custom but what is the tuning software? In other words what did you use to flash it?

In addition to the things you mentioned, it could be the LPFP.
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      08-09-2021, 03:29 PM   #6
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Quote:
Originally Posted by bobbykolev View Post
No issue with LPFP. 6.8 bar always, never dropped lower than normal.

He flashed it directly through ECU port. Didnt use OBD.
But what programme he uses, i have no idea...
What are you using to read LPFP pressure to know its 6.8 bar? AFAIK there is no OEM LPFP pressure sensor?

You may need to look into some other app to be able to datalog, there are some free ones with limited logging capabilities. It's not really possible to discern anything from the screenshot you posted.
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      08-09-2021, 06:03 PM   #7
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The guy who tuned the car told me that there is no LPFP issue he saw that it stands at 6.8 bar.
Dunno which app i can use for datalog. Can u recommend?

Quote:
Originally Posted by thejeremyman9 View Post
What are you using to read LPFP pressure to know its 6.8 bar? AFAIK there is no OEM LPFP pressure sensor?

You may need to look into some other app to be able to datalog, there are some free ones with limited logging capabilities. It's not really possible to discern anything from the screenshot you posted.
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      08-09-2021, 06:10 PM   #8
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This night i made more than 15 runs. First 10 i tries everythinf. From 1st to 6th full throttle. 3rd to 6th and 4th to 6th full throttle. Only 5th full throttle. The fuel preaaure stays at 200-205 bar and doesnt move. I just dont know what ia going on.... I when i stopped the car low engine oil lamp came on. I filled around 600 ml and the car was full. After that i launched it and again from 200-205 on 3rd gear dropped to 135-140 bar. Few more launches and it was dropping again but not that much from 205 to 170 which i didnt really feel only saw it on the live data rec.
What the f*** is going on with that car....
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      08-10-2021, 12:15 PM   #9
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Quote:
Originally Posted by bobbykolev View Post
This night i made more than 15 runs. First 10 i tries everythinf. From 1st to 6th full throttle. 3rd to 6th and 4th to 6th full throttle. Only 5th full throttle. The fuel preaaure stays at 200-205 bar and doesnt move. I just dont know what ia going on.... I when i stopped the car low engine oil lamp came on. I filled around 600 ml and the car was full. After that i launched it and again from 200-205 on 3rd gear dropped to 135-140 bar. Few more launches and it was dropping again but not that much from 205 to 170 which i didnt really feel only saw it on the live data rec.
What the f*** is going on with that car....
Just to confirm the fuel you are running does not have any ethanol (or at least not above like 10%)? Its just gasoline?
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      08-10-2021, 01:41 PM   #10
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Quote:
Originally Posted by thejeremyman9 View Post
Just to confirm the fuel you are running does not have any ethanol (or at least not above like 10%)? Its just gasoline?
Just out of curiosity. How would a higher ethanol content play a roll in a sudden crash like the one he is displaying?

Thanks
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      08-10-2021, 02:39 PM   #11
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Quote:
Originally Posted by GAB0 View Post
Just out of curiosity. How would a higher ethanol content play a roll in a sudden crash like the one he is displaying?

Thanks
I run E30 fuel on the MHD stage 2+ E20 map. I sometimes get a very brief dip in HPFP pressure before it stabilizes the rest of the pull. I know i am operating near the stock HPFP limit. In other words you can see brief dips in HPFP pressure without a full "crash", especially if you are pushing the hardware limits with your boost/fueling.

We (I) know very little about the system/sensor that controls the HPFP pressure. There was a little discussion about it a while back but all speculation and I've never seen any official documentation/description of the system/sensor. The general guidance/rule of thumb is just upgrade the HPFP if you need the extra fueling - in other words no way to manipulate the system that's controlling the high pressure to get anything more out of the mechanical HPFP. Just increase fuel supply.

The main question I've always had is that, if your HPFP pressure "crashes" (i.e., because you are demanding more fuel than it can supply), does this actually mean that the system controlling it is fully closed and you aren't returning any to the tank? I don't think we know for certain...

In OP's case the similar question i have is, is this system just responding too slow? Maybe its returning too much fuel to the tank for that brief moment causing the pressure dip? Presumable hes not demanding too much fuel or else his HPFP would continue to fall behind, but this depends on his fuel used, or it could be a situation similar to mine.
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      08-10-2021, 03:05 PM   #12
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Quote:
Originally Posted by thejeremyman9 View Post
I run E30 fuel on the MHD stage 2+ E20 map. I sometimes get a very brief dip in HPFP pressure before it stabilizes the rest of the pull. I know i am operating near the stock HPFP limit. In other words you can see brief dips in HPFP pressure without a full "crash", especially if you are pushing the hardware limits with your boost/fueling.

We (I) know very little about the system/sensor that controls the HPFP pressure. There was a little discussion about it a while back but all speculation and I've never seen any official documentation/description of the system/sensor. The general guidance/rule of thumb is just upgrade the HPFP if you need the extra fueling - in other words no way to manipulate the system that's controlling the high pressure to get anything more out of the mechanical HPFP. Just increase fuel supply.

The main question I've always had is that, if your HPFP pressure "crashes" (i.e., because you are demanding more fuel than it can supply), does this actually mean that the system controlling it is fully closed and you aren't returning any to the tank? I don't think we know for certain...

In OP's case the similar question i have is, is this system just responding too slow? Maybe its returning too much fuel to the tank for that brief moment causing the pressure dip? Presumable hes not demanding too much fuel or else his HPFP would continue to fall behind, but this depends on his fuel used, or it could be a situation similar to mine.
Thank you for the detailed response. The reason I asked is because I've had a similar dip in my car. The lowest HPFP reading came in at 1678 PSI. In my case I'm on the BM3 Stage 1 map. I got in the habit of adding 1.5 to 3 gallons of E85 to my 91 octane fuel. The dip happened while on higher ethanol content (2.5 gallons of E85). I've since lowered it to 1-1.5 gallons of E85 and the dip has not returned. Granted I've been adding E85 inconsistently on a weekly basis. That is to say sometimes I'll add 3 gallons and other times just one.

I noticed the dip took place right when the car hit full boost and the quickly normalized with no other dips. The car accelerated smoothly with no hiccups.

Last edited by GAB0; 08-10-2021 at 03:16 PM..
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      08-10-2021, 03:44 PM   #13
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Quote:
Originally Posted by GAB0 View Post
Thank you for the detailed response. The reason I asked is because I've had a similar dip in my car. The lowest HPFP reading came in at 1678 PSI. In my case I'm on the BM3 Stage 1 map. I got in the habit of adding 1.5 to 3 gallons of E85 to my 91 octane fuel. The dip happened while on higher ethanol content (2.5 gallons of E85). I've since lowered it to 1-1.5 gallons of E85 and the dip has not returned. Granted I've been adding E85 inconsistently on a weekly basis. That is to say sometimes I'll add 3 gallons and other times just one.

I noticed the dip took place right when the car hit full boost and the quickly normalized with no other dips. The car accelerated smoothly with no hiccups.
Yup, similar to what i get sometimes and what it seems is happening to OP. I wouldnt worry about it unless you are dropping well below 1500 psi, and/or the drop is lasting or recurring throughout the pull and not just on tip in.

Typically its only a problem/"crash" when you HPFP drops to <1000psi and stays there without recovering. You can usually tell from your fuel trims whether or not the pressure dropped low enough to actually affect fuel delivery as the DME will increase fuel trims to try and compensate for a leaner AFR.
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      08-11-2021, 05:49 AM   #14
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Standard 10% ethanol. Here we dont have ethanol mix like you in USA. Just standard Fuel 95,98,100 RON

Quote:
Originally Posted by thejeremyman9 View Post
Just to confirm the fuel you are running does not have any ethanol (or at least not above like 10%)? Its just gasoline?
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      08-11-2021, 02:05 PM   #15
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Quote:
Originally Posted by bobbykolev View Post
Standard 10% ethanol. Here we dont have ethanol mix like you in USA. Just standard Fuel 95,98,100 RON
I wouldn't obsess over it if its just a very brief drop and there are no impacts on actual fuel delivery or performance.
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      08-12-2021, 03:45 AM   #16
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Most of the time you feel it. This affects the acceleration time a lot... You feel it on 2nd and 3rd gear. The car is tuned and the best 0-100km/h is 4.3. The previous flash i had 3.85 0-100.
With last tune at low gear the car doesnt make a lot of power... I know the sport display isnt accurate but i know it was before this tune .... But i can really tell that the drop isnt as big as it was with the previous tune. Now drops between 145 and 165 bar, and with the previous tune it was dropping below 95 bars...
Today I ordered brand new injectors from bosch i hope this dropped will be sorted out because i want to buy WMI for the chargepipe.

Quote:
Originally Posted by thejeremyman9 View Post
I wouldn't obsess over it if its just a very brief drop and there are no impacts on actual fuel delivery or performance.
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      08-12-2021, 07:14 AM   #17
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Quote:
Originally Posted by thejeremyman9 View Post

We (I) know very little about the system/sensor that controls the HPFP pressure. There was a little discussion about it a while back but all speculation and I've never seen any official documentation/description of the system/sensor.

This should quench your thirst. Last years class on GDI engines, and how the systems work. Some of the info is common knowledge, some of it is more in depth than you could ever imagine (Need more fuel pressure? delay the injection time so the fuel pump cam lobe is closer to TDC of the lobe).

https://drive.google.com/file/d/1mj2...ew?usp=sharing
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      08-12-2021, 11:34 AM   #18
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Quote:
Originally Posted by bobbykolev View Post
Most of the time you feel it. This affects the acceleration time a lot... You feel it on 2nd and 3rd gear. The car is tuned and the best 0-100km/h is 4.3. The previous flash i had 3.85 0-100.
With last tune at low gear the car doesnt make a lot of power... I know the sport display isnt accurate but i know it was before this tune .... But i can really tell that the drop isnt as big as it was with the previous tune. Now drops between 145 and 165 bar, and with the previous tune it was dropping below 95 bars...
Today I ordered brand new injectors from bosch i hope this dropped will be sorted out because i want to buy WMI for the chargepipe.
If it behaves differently on different tunes what makes you think its the injectors?
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      08-12-2021, 11:35 AM   #19
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Quote:
Originally Posted by LA1Z24 View Post
This should quench your thirst. Last years class on GDI engines, and how the systems work. Some of the info is common knowledge, some of it is more in depth than you could ever imagine (Need more fuel pressure? delay the injection time so the fuel pump cam lobe is closer to TDC of the lobe).

https://drive.google.com/file/d/1mj2...ew?usp=sharing
Thanks, i actually have that in my downloads, so you probably posted it before lol. It does look pretty detailed, but not a lot specific to BMW.
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