What's causing my tune to break up in 5th gear?

[Z4m40i]

Car is running on an e40 custom flex fuel tune, but I will sometimes have to flex down to e25-e30 at the track depending on how much e85 I bring to the track.

99% of the time the car is running great, but I noticed only sometimes in 5th gear in WOT, the timing will retard and the car will try to make up the torque difference by adding more boost. STFT shows its adding a lot of fuel to make up the difference, and AFR richens up to around 12. Additionally, this is somehow affecting the vanos exhaust actual which has triggered limp mode a couple of times. This doesn't seem to be an issue in any other gear and happens regardless of what ethanol content I'm running; however, it does seem to happen more frequently with e25-e30.

bootmod3 datalog - 5th gear boost spike
https://www.bootmod3.net/log?id=67a93bce2c00ea6dcbfc0320

I imagine the lower octane fuel is causing it to retard, but I'm under the impression that the flex fuel factor should be compensating for this.

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[razorlab]

That is one aggressive tune. Timing isn't happy. Lot's of boost.

Is the issue happening on the shift into 5th? In the first log, the HPFP maxes out and AFR is a bit lean at the shift into 5th. Also your vanos target/actual is way off.

 

[Z4m40i]

If i'm doing a 4th gear log pull, it's almost always clean. Boost usually targets around 24.5-27PSI

bootmod3 datalog - flex fuel multimap

4th-6th gear looks pretty good there, and this is how it is a majority of the time. (e40 fuel)

bootmod3 datalog - flex fuel multimap
3rd-5th gear also looks pretty stable (e40 fuel)

bootmod3 datalog - flex fuel multimap
This was with e35 fuel but notice how only 5th gear seems to fall apart at top, but then recovers in 6th gear.

bootmod3 datalog - flex fuel multimap
e35 fuel, same session, and now 5th gear looks fine.

I'm just confused as to why it seems to happen sometimes... I brought this up to my tuner, but I'm not sure if this is something tuning or mechanical.

 

[ColonelAdama]

I gotta wonder how this flex tune actually works if insufficient octane literally provokes the car to target 42 psi at redline lol.

My understanding was that flex tunes kept boost levels similar and adjusted base timing based on E%. If it compensates timing corrections with boost to hit the same load, what's the point?

I sort of get the impression this isn't a flex map, its an E40 map run on E25. Or too aggressive of a flex map like Bryan said

 

[razorlab]

I gotta wonder how this flex tune actually works if insufficient octane literally provokes the car to target 42 psi at redline lol.

My understanding was that flex tunes kept boost levels similar and adjusted base timing based on E%. If it compensates timing corrections with boost to hit the same load, what's the point?

I sort of get the impression this isn't a flex map, its an E40 map run on E25. Or too aggressive of a flex map like Bryan said

Yea something is def up with this tune.

As far as flex and boost. It depends on the tuner and the turbo. With a turbo that flows more, you should def target more boost with higher ethanol content.

 

[razorlab]

If i'm doing a 4th gear log pull, it's almost always clean. Boost usually targets around 24.5-27PSI

bootmod3 datalog - flex fuel multimap

4th-6th gear looks pretty good there, and this is how it is a majority of the time. (e40 fuel)

bootmod3 datalog - flex fuel multimap
3rd-5th gear also looks pretty stable (e40 fuel)

bootmod3 datalog - flex fuel multimap
This was with e35 fuel but notice how only 5th gear seems to fall apart at top, but then recovers in 6th gear.

bootmod3 datalog - flex fuel multimap
e35 fuel, same session, and now 5th gear looks fine.

I'm just confused as to why it seems to happen sometimes... I brought this up to my tuner, but I'm not sure if this is something tuning or mechanical.

I think I know what might be happening here. I found an issue awhile back with the Max Boost Reading table. If you don't raise it, boost can spiral out of control and shoots for the moon. I noticed that it was easily provoked when I went to a track at higher elevation (Pocono) as well. That is where it really showed itself.

However, my boost target wouldn't change. This may or may not be the same issue you are having.

The fix was scaling this table from 3300 to 4000

 

[Z4m40i]

Awesome man, thanks for the suggestion. I’m waiting to hear back from my tuner but I’ll pass this along. Unfortunately I won’t be able to verify any fixes until the end of the month when I’m back at Laguna Seca.

 

[letsrollmike]

Awesome man, thanks for the suggestion. I’m waiting to hear back from my tuner but I’ll pass this along. Unfortunately I won’t be able to verify any fixes until the end of the month when I’m back at Laguna Seca.

Laguna! I’m jelly. Best of luck hope you get it fixed.

 

[Z4m40i]

I think I know what might be happening here. I found an issue awhile back with the Max Boost Reading table. If you don't raise it, boost can spiral out of control and shoots for the moon. I noticed that it was easily provoked when I went to a track at higher elevation (Pocono) as well. That is where it really showed itself.

However, my boost target wouldn't change. This may or may not be the same issue you are having.

The fix was scaling this table from 3300 to 4000

I passed that info along and the response was, "he's talking about PVDMX and that is set to 3500/35PSI so that should not be the issue".

Tuner is still under the impression that the boost spiking in 5th is related to "cam walk" which causes the VANOS Exhaust to come off target. We're bumping up the oil pressure a little more to see if that solves this- assuming that the VANOS actuator and bolt are okay. I'll be adding the Verus oil cooler this weekend and I'm curious how this further impacts this.

I'm still a little confused on the influence of HPFP, fuel rail and oil pressure (and now apparently boost pressure) and how it affects the Exhaust VANOS... and even more confused about what the Exhaust Vanos value in the log is measuring.

 

[i3igpete]

I'm still a little confused on the influence of HPFP, fuel rail and oil pressure (and now apparently boost pressure) and how it affects the Exhaust VANOS... and even more confused about what the Exhaust Vanos value in the log is measuring.

The high pressure fuel pump is on the exhaust cam. During every pumping event, error will build depending on the injected volume (scales with rail pressure, pump plunger diameter, pump lift, injection duration). Unlike stiffer valve springs, the energy to drive the fuel pump is not returned to the cam when the plunger returns to base radius.

vanos is a cam phaser system. it uses oil pressure to either make chamber A bigger or chamber B bigger. that's all it is. Think of it this way: suppose the entire assembly (green and yellow) is spinning clockwise. When the high pressure fuel pump is lifting, it's puts a CCW torque on the yellow body. This squeezes some fluid out of chamber B due to leakage paths. The oil pump has to refill chamber B before the next pumping event. If not, B is too small and now you have retard/delay error. the exhaust cams, which are also on the yellow body, now open the valves way too late.

Increasing oil pump pressure allows you to attempt to refill chamber B faster. However, this only treats the symptom, the error is still accumulating with each lift event.

Other methods to treat this include running a lower rail pressure with larger injectors so that you can achieve the same injected volume but with less torque load coming from the pump. Or, God forbid, an aftermarket company doing some actual engineering work to change the internal phaser geometry.

 

[razorlab]

I passed that info along and the response was, "he's talking about PVDMX and that is set to 3500/35PSI so that should not be the issue".

Tuner is still under the impression that the boost spiking in 5th is related to "cam walk" which causes the VANOS Exhaust to come off target. We're bumping up the oil pressure a little more to see if that solves this- assuming that the VANOS actuator and bolt are okay. I'll be adding the Verus oil cooler this weekend and I'm curious how this further impacts this.

I'm still a little confused on the influence of HPFP, fuel rail and oil pressure (and now apparently boost pressure) and how it affects the Exhaust VANOS... and even more confused about what the Exhaust Vanos value in the log is measuring.

Yea I called out the exhaust cam deviation in the log before.

HPFP is driven off the cam, which can be affected by a stiffer/upgraded HPFP. Oil pressure controls the VANOS adjustment.

The measurement is angle.

 

[razorlab]

Tuner is still under the impression that the boost spiking in 5th is related to "cam walk" which causes the VANOS Exhaust to come off target. We're bumping up the oil pressure a little more to see if that solves this- assuming that the VANOS actuator and bolt are okay. I'll be adding the Verus oil cooler this weekend and I'm curious how this further impacts this.

The only counter I have to that is that your boost target is ALSO changing. If it was just boost going over target, I would say his hypothesis could be correct.

Also, the logged oil pressure is also not changing when the exhaust cam deviates from target.

 

[garudathree]

I had a bunch of exhaust vanos deviation when the oil pump was having issues and running in safe/emergency mode.

 

[Z4m40i]

Thanks for the explanation of it guys. Gotta do more research on how VVT works in general.

@garudathree luckily I havent noticed any issues with my oil pressure above 80psig, and I’m able to check oil level without issue.

@razorlab agree with you on the oil pressure not deviating so the proposed solution seems a little sus. I compared oil pressure on all logs and oil pressure doesn’t fall off . I don’t know why boost target would change if BM3 doesn’t do boost by gear; however, he says it apparently can happen when the exhaust target is off and sees it often when it does.

What would make since in this case- exhaust vanos is falling off which is influencing the boost, or boost is shooting up and influencing the vanos to fall off?

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