Z4m40i
Well-Known Member
- First Name
- Justin
- Joined
- Nov 30, 2023
- Threads
- 9
- Messages
- 156
- Reaction score
- 175
- Location
- Salt Lake City
- Car(s)
- 2020 BMW z4 m40i, 2020 BMW X7 40i
Since I'm currently chasing this issue, I figured I will also share my research. Short story, for most people newly encountering this issue after adding power and/or HPFP, this is tuning related.
To preface, I had a tune finalized w/ stock HPFP and pure850. The stock pump was pushed to its limit, and there were some scenarios where the rail pressure would drop slightly. I added a dorch HPFP after the fact, and did not have a revision. I added this before a track day w/o a revision for a few reasons:
1) Dorch said this was 100% p&p (have to select the bm3 option)
2) I wanted the additional overhead at the track.
3) I'm adding s58 injectors, so I don't want my tuner wasting time with revisions on the old setup.
To my knowledge, there isn't a boost "limit" on these cars, and the DME will use boost as one of the strategies to hit load targets. This is supported from logs on the same tune where it seems both the exhaust vanos and fuel rail pressure hit target 100% during a pull, and other times where fuel rail pressure dropped and/or exhaust vanos deviated from target.
My impression is that there are two scenarios that will cause this error code
1) DME detects one large acute deviation from exhaust vanos actual to target (greater than >40 delta)
2)DME consistently detects a sizeable deviation from exhaust vanos actual to target (around 30 delta)
My tuner said that gen2 b58's are "notorious for exhaust cam walk", and the problem becomes accentuated with aftermarket HPFP's. Dorch didn't confirm this as the issue, but did elude to how stock HPFPs will also have this issue when adding more power. My tuners said that it's common for vanos to fall off target under high boost and/or high RPM, but we can combat this by dropping rail pressure and increase oil pressure. Additionally, he said to reset VANOS and VVT adaptations in bm3.
The nice thing is that for most people, this is a solvable solution via tune. I'm surprised that this doesn't seem to be well documented as this seems like a common side effect from increasing power with a DI system.
From dorch:
"That fault code isn’t necessarily associated with what you are seeing with the vanos mismatch, it really just depends on the conditions of the fault snapshots in ISTA. If it’s happening only at high RPM in the snapshots, then you can be pretty confident that it’s due to your power level/HPFP and it can be tuned for. Otherwise, if it’s random and at startup or cruise, then you’ll want to look into some vanos replacement parts a bit more carefully. To answer your question, yes, a larger HPFP can contribute to this issue when not properly tuned for, but generally speaking these cars have this issue in stock form and it gets worse and worse the more power you make (regardless of HPFP choice). For example, pretty much anything past stock turbos on an S58 car requires a vanos lockout on the exhaust side along with ALL fast drag Supras. It’s not mentioned much, because people seem to think this is some special secret, but the big power guys in B58 and S58 all have locked out exhaust vanos to avoid what you’re seeing. The good news is that at your power level it can be fixed with tuning alone. Let us know if you have any other questions! "
To preface, I had a tune finalized w/ stock HPFP and pure850. The stock pump was pushed to its limit, and there were some scenarios where the rail pressure would drop slightly. I added a dorch HPFP after the fact, and did not have a revision. I added this before a track day w/o a revision for a few reasons:
1) Dorch said this was 100% p&p (have to select the bm3 option)
2) I wanted the additional overhead at the track.
3) I'm adding s58 injectors, so I don't want my tuner wasting time with revisions on the old setup.
To my knowledge, there isn't a boost "limit" on these cars, and the DME will use boost as one of the strategies to hit load targets. This is supported from logs on the same tune where it seems both the exhaust vanos and fuel rail pressure hit target 100% during a pull, and other times where fuel rail pressure dropped and/or exhaust vanos deviated from target.
My impression is that there are two scenarios that will cause this error code
1) DME detects one large acute deviation from exhaust vanos actual to target (greater than >40 delta)
2)DME consistently detects a sizeable deviation from exhaust vanos actual to target (around 30 delta)
My tuner said that gen2 b58's are "notorious for exhaust cam walk", and the problem becomes accentuated with aftermarket HPFP's. Dorch didn't confirm this as the issue, but did elude to how stock HPFPs will also have this issue when adding more power. My tuners said that it's common for vanos to fall off target under high boost and/or high RPM, but we can combat this by dropping rail pressure and increase oil pressure. Additionally, he said to reset VANOS and VVT adaptations in bm3.
The nice thing is that for most people, this is a solvable solution via tune. I'm surprised that this doesn't seem to be well documented as this seems like a common side effect from increasing power with a DI system.
From dorch:
"That fault code isn’t necessarily associated with what you are seeing with the vanos mismatch, it really just depends on the conditions of the fault snapshots in ISTA. If it’s happening only at high RPM in the snapshots, then you can be pretty confident that it’s due to your power level/HPFP and it can be tuned for. Otherwise, if it’s random and at startup or cruise, then you’ll want to look into some vanos replacement parts a bit more carefully. To answer your question, yes, a larger HPFP can contribute to this issue when not properly tuned for, but generally speaking these cars have this issue in stock form and it gets worse and worse the more power you make (regardless of HPFP choice). For example, pretty much anything past stock turbos on an S58 car requires a vanos lockout on the exhaust side along with ALL fast drag Supras. It’s not mentioned much, because people seem to think this is some special secret, but the big power guys in B58 and S58 all have locked out exhaust vanos to avoid what you’re seeing. The good news is that at your power level it can be fixed with tuning alone. Let us know if you have any other questions! "
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