[rallas]

I think I am having issues with the high pressure fuel pump on my '16 435i running stage 2 93 octane BM3. In the logs below I am experiencing high RPM full load breakup and it is more pronounced in the lower gears(<4th). The actual fuel pressure drops way below target at higher RPM where it usually stays real close to target pressures at all times. Timing starts to get squirelly sime times, but seems to happen after fuel pressures take a dive. I will be changing plugs as a precaution too since I think I have about 20k miles on these plugs. Coils were replaced when I changed plugs last.

I am getting ready to order a new high pressure pump, but wanted to get confirmation from more experienced N55 log reviewers before I do so.

https://www.bootmod3.net/log?id=655b...26081646ba86bc

https://www.bootmod3.net/log?id=655b...d6043ef68f9df2

[Eschmacher]

In that second log, you are down 1100psi from target at 5900rpm. Seems like a pretty clear HPFP issue to me.

[rallas]

Yup, my thoughts exactly.

[thejeremyman9]

So i would say yes you can conclude that the HPFP is not keeping up with demand, but before you go throwing a HPFP at it, the question is why not? The stock HPFP should be fine for OTS stage 2 pump gas map, assuming you are not adding any ethanol.

You dont have STFTs in your log or AFR target. It looks potentially slightly rich just going based off memory, especially in 5th gear. The HPFP may be fine but if the car is commanding too much fuel the HPFP cant keep up.

It would be very unusual for a HPFP to 'partially fail' since its mechanical. There have also been several cases of other issues making fuel pressure drop (AFR/fuel trim problems) even though the HPFP itself is fine.

I would relog with STFT, LTFT, and AFR target enabled

[n55david]

Could be a lpfp issue as well.. js

[5w20]

Originally Posted by n55david

You be a lpfp issue as well.. js

Right on.


I'm not sure how one can conclude that this is 100% a HPFP issue, without doing any type of diagnosis on the low pressure side. Take a minute to sit back and think how this fuel system works.

[rallas]

I was going to ask how to diagnose lpfp since we do not have a real low pressure sensor on the N55.

To me it looks like a high load high rpm hpfp crash, but I guess if the lpfp was starving the hpfp at peak flow it could cause the rail pressures to drop like it shows in my logs.

I ended up ordering the new hpfp, but after seeing how the intake and stuff has to come out to get to the pump I might just get a lpfp since it is relatively cheap and easier to replace. At least to eliminate it as a the source of the problem. I am at 94k miles and getting ready for a bunch or preventative 100k maintenance (oil filter/cooler gasket, hoses, water pump, thermostat, transmission (did this one previously at 60k) and diff fluid, oil pan gasket with a contingency to replace rod bearings) and might as well include the lpfp too. I want this one to reach 200k miles so adding a $130 lpfp is a no brainer.

[thejeremyman9]

Originally Posted by rallas

I was going to ask how to diagnose lpfp since we do not have a real low pressure sensor on the N55.

To me it looks like a high load high rpm hpfp crash, but I guess if the lpfp was starving the hpfp at peak flow it could cause the rail pressures to drop like it shows in my logs.

I ended up ordering the new hpfp, but after seeing how the intake and stuff has to come out to get to the pump I might just get a lpfp since it is relatively cheap and easier to replace. At least to eliminate it as a the source of the problem. I am at 94k miles and getting ready for a bunch or preventative 100k maintenance (oil filter/cooler gasket, hoses, water pump, thermostat, transmission (did this one previously at 60k) and diff fluid, oil pan gasket with a contingency to replace rod bearings) and might as well include the lpfp too. I want this one to reach 200k miles so adding a $130 lpfp is a no brainer.

My overall point/question remains; why are you running out of fuel on a pump gas map? I would relog with the parameters i mentioned to confirm its not an AFR/fuel trim/software issue.

If you are truly just exceeding HPFP flow capacity, that usually happens at low RPM high load/boost, because the HPFP flow is RPM dependent. When you demand a bunch of fuel at low RPM that's usually when it crashes.

[5w20]

Originally Posted by rallas

I was going to ask how to diagnose lpfp since we do not have a real low pressure sensor on the N55.

To me it looks like a high load high rpm hpfp crash, but I guess if the lpfp was starving the hpfp at peak flow it could cause the rail pressures to drop like it shows in my logs.

I ended up ordering the new hpfp, but after seeing how the intake and stuff has to come out to get to the pump I might just get a lpfp since it is relatively cheap and easier to replace. At least to eliminate it as a the source of the problem. I am at 94k miles and getting ready for a bunch or preventative 100k maintenance (oil filter/cooler gasket, hoses, water pump, thermostat, transmission (did this one previously at 60k) and diff fluid, oil pan gasket with a contingency to replace rod bearings) and might as well include the lpfp too. I want this one to reach 200k miles so adding a $130 lpfp is a no brainer.

There's a few really easy ways.

If you have the flex fuel sensor setup, some have the option of installing an electrical or mechanical gauge. If you don't have the FF sensor setup, you can install a mechanical gauge in the same exact spot as where the FF sensor setup would go. Doesn't take but a few minutes to set it up.

[rallas]

Originally Posted by thejeremyman9

My overall point/question remains; why are you running out of fuel on a pump gas map? I would relog with the parameters i mentioned to confirm its not an AFR/fuel trim/software issue.

If you are truly just exceeding HPFP flow capacity, that usually happens at low RPM high load/boost, because the HPFP flow is RPM dependent. When you demand a bunch of fuel at low RPM that's usually when it crashes.

I have been running with this Stage 2 93 Octane tune for two years now with no issues. I did not just switch to the tune and them realize I am exceeding pump capacity. It appears that one of my fuel pumps has degraded since I never had this high RPM high load problem untill 2 weeks ago.

The reports I have seen with hpfp crashing is not just at mid loads. Peak fuel flow is needed at high load AND high rpm. When either pump can't keep up, rail pressure tanks.

[thejeremyman9]

Originally Posted by rallas

I have been running with this Stage 2 93 Octane tune for two years now with no issues. I did not just switch to the tune and them realize I am exceeding pump capacity. It appears that one of my fuel pumps has degraded since I never had this high RPM high load problem untill 2 weeks ago.

The reports I have seen with hpfp crashing is not just at mid loads. Peak fuel flow is needed at high load AND high rpm. When either pump can't keep up, rail pressure tanks.

I know that's when peak flow is needed, but high rpm is also when the HPFP supplies the most fuel. And yes, i unerstand that rail pressure drops when fuel supply is insufficent, from either LPFP or HPFP. The question is why is fuel supply insufficient - is the demand higher than it should be, or is the supply actually inadequate?

Anyways, if you dont want to log to confirm its not a AFR or fuel trim issue causing the high fuel demand (there have been several cases of that), then you can throw some parts at the car and see what happens, hopefully it is indeed one of the pumps and your replacement solves the problem

[rallas]

AFR is included in the logs on the original post. It was one of the first things I looked at when the issue first started since I expected it to go way lean when fuel pressure dropepd >1000psi below target. I was surprised to not see it lean way out.

I added the short and long term fuel trims to my logs, but I flashed back to Stage 1 ACN after I noticed the issue to make sure I don't kill the pump. I still need to be able to drive the car for a few weeks before I will have time to replace any parts. On Stage 1 I do not experience high rpm issues, but the hpfp pressure is below target at lower RPM at full throttle/boost. Long term trims and short term trems vary very little. I will see if I can flash back to Stage 2 this weekend and repeat the pulls with the additional points logged.

https://www.bootmod3.net/log?id=6569...0e9f6d9cb34f09

[thejeremyman9]

Originally Posted by rallas

AFR is included in the logs on the original post. It was one of the first things I looked at when the issue first started since I expected it to go way lean when fuel pressure dropepd >1000psi below target. I was surprised to not see it lean way out.

I added the short and long term fuel trims to my logs, but I flashed back to Stage 1 ACN after I noticed the issue to make sure I don't kill the pump. I still need to be able to drive the car for a few weeks before I will have time to replace any parts. On Stage 1 I do not experience high rpm issues, but the hpfp pressure is below target at lower RPM at full throttle/boost. Long term trims and short term trems vary very little. I will see if I can flash back to Stage 2 this weekend and repeat the pulls with the additional points logged.

https://www.bootmod3.net/log?id=6569...0e9f6d9cb34f09

I meant AFR target sorry, i see normal AFR. The trims are close to 1 (infact STFT is "stuck" at 1 quite a bit) but nothing crazy is going on like fuel trims adding fuel when they dont need to be from what i saw

[rallas]

I can add AFR targets for future logs. Based on the trims looking close to 1 and AFRs being in the general range what I expect to see it did not appear to me that any crazy fueling changes are being requested by the DME. I am also not aware of any specific DME logic/tuning that would force a drop in fuel rail pressure like I am seeig.

I appreciate the challenge since it is making me think about what I could be missing. While I am confident that either the LPFP or HPFP will fix my issues, one thing I am not 100% sure of is if I could be having any injector issues.

From what I can tell, injector issues would be more apparent at all times and not just at high/full load and high RPM. Should I be looking at something specific to confirm my injectors are OK?

I have a good bit of experience tuning and troubleshooting issues with port injected engines, but I have to admit that the additional factors of direct injection engine operation is relatively new to me.

[thejeremyman9]

Originally Posted by rallas

I can add AFR targets for future logs. Based on the trims looking close to 1 and AFRs being in the general range what I expect to see it did not appear to me that any crazy fueling changes are being requested by the DME. I am also not aware of any specific DME logic/tuning that would force a drop in fuel rail pressure like I am seeig.

I appreciate the challenge since it is making me think about what I could be missing. While I am confident that either the LPFP or HPFP will fix my issues, one thing I am not 100% sure of is if I could be having any injector issues.

From what I can tell, injector issues would be more apparent at all times and not just at high/full load and high RPM. Should I be looking at something specific to confirm my injectors are OK?

I have a good bit of experience tuning and troubleshooting issues with port injected engines, but I have to admit that the additional factors of direct injection engine operation is relatively new to me.

For the first part, it's not that the DME logic would intentionally force a drop in fuel rail pressure. But there's a few examples where wonky things have caused fueling to me off and therefore caused rail pressure drops. Some recent examples:

1. LTFTs are affected from something like an intake (could be other things, MAF issue, etc), where LTFTs go positive, adding fuel that doesnt need to be there. STFTs can try to correct, but could result in extra fuel demand (extra compared to what the tune needs), exceeding HPFP capacity.

2. O2 sensor issue causes incorrect AFR readings. DME thinks engine is lean, adds a bunch of fuel with STFTs, creating extra fuel demand, exceeding HPFP capacity. Car in reality is running super rich.

Basically, the fuel demand from a pump gas map should be well within stock HPFP capacity. So the question is: is it a hardware issue, or is something causing extra fuel demand, and the pumps are working fine?

But yeah, you're right on - I just want to engage thinking critically before throwing parts at the car.

I don't think its necessarily an injector issue. Usually an injector is either having flow problems, supplying less fuel that needed. Or, its leaking, and you would have startup issues or see fuel being pulled in STFTs.

[rallas]

I did another Stage1 log, but in 4th gear this time. Usually I feel the the loss in power in the lower gears, but in this log you can see hpfp pressure fall well below target in mid range at full boost.

I think I added the wrong thing to log AFR target. I did not find anythong labeled AFR target and I think I might have picked the wrong Lambda value to log.


https://www.bootmod3.net/log?id=6571...01c949bd09d0d0

[thejeremyman9]

Originally Posted by rallas

I did another Stage1 log, but in 4th gear this time. Usually I feel the the loss in power in the lower gears, but in this log you can see hpfp pressure fall well below target in mid range at full boost.

I think I added the wrong thing to log AFR target. I did not find anythong labeled AFR target and I think I might have picked the wrong Lambda value to log.


https://www.bootmod3.net/log?id=6571...01c949bd09d0d0

I am not sure exactly what its called in BM3 but here's a MHD example: https://datazap.me/u/thejeremyman9/2...ta=12-13-22-24

I am a little suspicious of STFTs in your log. If you look closely, the HPFP pressure starts to fall below target right when the STFTs go from 1 to 1.11. Its just a correlation though, not necessarily causation. Also, the shape of the AFR curve is the same as the HPFP curve. It looks like the car went lean, STFTs added a bunch of fuel, HPFP pressure dropped and the car went too rich, then AFR went back up and stabilized and HPFP recovered. 3597 to 4558 rpm

[rallas]

Turns out it was the LPFP! I am glad it was only the LPFP. At first I thought the HPFP was a real simple and easy job, but then realized the intake has to come off. AND if i am going to take the intake off, I am also going to do the OFHG while I am in there. Instead it was a simple 30 minute LPFP swap.

Now everything seems to be working great! See 4th gear pull below.

I guess I will have a HPFP on hand if I need it in the future.
https://www.bootmod3.net/log?id=659d...9d7f1f1e61bdee

[rallas]

Dang it! I declared victory too early. On the data I logged this morning it looks like rail pressures are still tanking. Dropping more than 1000psi below target above 4400rpm at full load. See the 3rd to 4th gear data below. The ambient temps were below freezing today and IAT is almost 30 deg cooler than the data I shared 2 days ago. I guess the denser air wants to make more power and use more fuel, just pushing the HPFP beyond what it can currently supply.

I am convinced it is not something that is caused by other sensor or algorithm input. Target pressures remain constant during these times so there is no requested change in rail presure, but the HPFP just cannot seem to supply all the fuel needed at high load.

Time to plan a HPFP after all! I am already planning to do OFHG and clean valves while I have the intake off. Are there any other good to do maintenance to take care of while I have the intake off? I am at 95k miles.

https://www.bootmod3.net/log?id=659f...9d7f1f1e62d566

[5w20]

Keep guessing or start diagnosing.