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Discussion Starter · #1 ·
When should one be concerned about the car maxing out fuel trims trying to reach ECU targets for Air/Fuel ratio? Stock ECU targets 11.5 I believe, which is on the rich side. 14.7 is the internal combustion "ideal" mix according to a few articles I saw. JB4 added fuel control wires to target 12.5 AFR under load to enhance power. I have seen some logs lately (currently one on a sub-forum here) where trims are maxed out and the car is approaching 14-14.5 for several seconds.
Anyway, I see a lot of discussion about timing when adding boost over stock, but not much on safe AFR level so was hoping to mine some knowledge!
 

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I’d love to know too. Your post reaffirms to me that the previous owner of my car got it tuned. My timing is really really advanced, and my AFR is usually around 14.7. At this point, I wish I could find the previous owner! I have some questions for them!!!
 
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14.7 AFR is the typical when the car is not under load, i.e. idling or cruising on the freeway. Under full throttle, you want it to be on the "rich side". From what I have seen, anything between 10.8-12.1 seems to be considered safe. You go above that and you really need to start monitoring Exhaust Gas Temps. What that EGT should be is over my head.
 

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When should one be concerned about the car maxing out fuel trims trying to reach ECU targets for Air/Fuel ratio? Stock ECU targets 11.5 I believe, which is on the rich side. 14.7 is the internal combustion "ideal" mix according to a few articles I saw. JB4 added fuel control wires to target 12.5 AFR under load to enhance power. I have seen some logs lately (currently one on a sub-forum here) where trims are maxed out and the car is approaching 14-14.5 for several seconds.
Anyway, I see a lot of discussion about timing when adding boost over stock, but not much on safe AFR level so was hoping to mine some knowledge!
good question and glad you asked! i'll be checking to see what others have to say.
 

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this is a big subject. suffice to say that 14:1 isnt typically normal for WOT but AFRs that high can be achieved under load in a GDI turbo engine because of how direct injection works. i dunno about the VR30 but AFRs as high as 60:1 can be achieved in part throttle operation. gdi engines in general tend to run much leaner that pfi engines.

afrs that go lean as rpm rises usually indicates an inadequate fuel system as no tuner in their right mind would make it easier for an engine to detonate as load/speed increases.

this thread could get monsterous, lol. theres so much more to this.
 

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Idle, cruising and very light load should be 14.7. As load increases afr should richen.

For NA applications the WOT target sweet spot is typically around 12.5, even richer at around 11.5 for FI. Now direct injection can typically run about .5 afr leaner safely vs port injections, so 11.5-12.0 is typically a good safe target for vr30s. But there are obviously a lot of variables to consider. And logging and identifying pre detention and/or knock events would be the best way to know for certain.
 

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Discussion Starter · #7 ·
I guess the question is, if the car is maxing out trims at full throttle but still running AFR at say 13.5 or 14...is that safe? Secondary question is, why some cars can't deliver fuel fast enough at say 16psi boost when others are running 18+ PSI before hitting the fuel pump's limitations?
 

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I guess the question is, if the car is maxing out trims at full throttle but still running AFR at say 13.5 or 14...is that safe? Secondary question is, why some cars can't deliver fuel fast enough at say 16psi boost when others are running 18+ PSI before hitting the fuel pump's limitations?
I would not consider 13.5 safe.

If you wanted to max fuel trims but still be “safe” i would
1. Make sure log looks good, no unusual timing drops.
2. make sure afr is good preferably sub 12.2 IMO
3. Slowly raise boost and watch trims increase so you know it’s right at max as opposed to being maxed but really “wanting” well beyond max.
IE +4psi puts you at +32, +5psi puts you at +38, and +6psi puts you at +44 your trims actually are probably at or very close to +44, but +7 would put you at +50 however +44 is max so now it’s unable to compensate for what it would really want. In this case assuming steps 1-2 checked out I would run +6 psi.
 

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I guess the question is, if the car is maxing out trims at full throttle but still running AFR at say 13.5 or 14...is that safe? Secondary question is, why some cars can't deliver fuel fast enough at say 16psi boost when others are running 18+ PSI before hitting the fuel pump's limitations?
For your 1st question, no, that is not safe. Fuel has a cooling and lubricating effect. When the engine is under heavy load, it needs more fuel, not just for combustion but to cool and lubricate the top end.
Your 2nd question. There are a lot of variables that go into that. Air intake temps, type of fuel, octane of fuel, fuel quality, fuel pump and injector efficiency. Like 17awd said, I would be more worried about knock than trying to raise the AFR. Depending on fuel and air temps, your AFR might need to be 11.0 to not have knock. Water/meth injection, higher octane and cooler air temps can all help you to run higher AFR's and as a result crank up the boost more without maxing fuel delivery. Again, using knock as your guide. I see you don't have an upgraded HX in your signature, I would start there.
 

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Discussion Starter · #10 · (Edited)
IRSBlueRS really appreciate detailed explanations. I personally am not having this issue - just helping some others interpret their logs. Unfortunately the ones seeing the lean AFR values are not trying to lean out the AFR, their fuel pump just can't keep up at relative conservative boost levels of 15-16PSI. The timing on their logs look good so it is frustrating for them to have to back the boost back down due to running too lean.
For the guys who ae tuned...Burger is targeting 12.5 AFR with the JB4 fuel wires. What are the individualized tuners targeting when they are pushing out 18+ PSI boost on stock fuel pumps? What AFR is being achieved in the logs?

17awdQ50P - Thanks for the advice - we need this kind of knowledge out there because JB4 has turned a bunch of us novices into tuners on our expensive cars!!
On your #1 - exactly - Timing is primary parameter I had been looking at when reviewing logs for new JB4 owners looking for some feedback.
On your #2, Burger is targeting 12.5 as ideal but safe to generate power so above that is where I was starting to express concern and seek some more advice before telling someone "no-you can't run that much boost". Pretty close to the 12.2 you advise above.
As for #3 - totally agree, which is why I started the thread. Was just looking for the right cutoff and a better understanding of the science/engineering behind it.
 

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IRSBlueRS really appreciate detailed explanations. I personally am not having this issue - just helping some others interpret their logs. Unfortunately the ones seeing the lean AFR values are not trying to lean out the AFR, their fuel pump just can't keep up at relative conservative boost levels of 15-16PSI. The timing on their logs look good so it is frustrating for them to have to back the boost back down due to running too lean.
For the guys who ae tuned...Burger is targeting 12.5 AFR with the JB4 fuel wires. What are the individualized tuners targeting when they are pushing out 18+ PSI boost on stock fuel pumps? What AFR is being achieved in the logs?

17awdQ50P - Thanks for the advice - we need this kind of knowledge out there because JB4 has turned a bunch of us novices into tuners on our expensive cars!!
On your #1 - exactly - Timing is primary parameter I had been looking at when reviewing logs for new JB4 owners looking for some feedback.
On your #2, Burger is targeting 12.5 as ideal but safe to generate power so above that is where I was starting to express concern and seek some more advice before telling someone "no-you can't run that much boost". Pretty close to the 12.2 you advise above.
As for #3 - totally agree, which is why I started the thread. Was just looking for the right cutoff and a better understanding of the science/engineering behind it.
Where are you getting "Burger is targeting 12.5 as ideal but safe to generate power" and in what context?
 

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Discussion Starter · #12 ·
Swore I saw it posted on the N54 site somewhere but can't put my finger on it. Its a mess of thousands of posts. Wish they would just post their parameters in one place as a resource! Looking at my own logs with fuel wires, I seem to average around 12.5 so seemed reasonable confirmation bias of what I thought I read somewhere.
Also - "Ideal but Safe" were my words. IF I read the target is 12.5, they did not say it in that way. I just implied that as a rationale for why they chose to target 12.5.
 

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Swore I saw it posted on the N54 site somewhere but can't put my finger on it. Its a mess of thousands of posts. Wish they would just post their parameters in one place as a resource! Looking at my own logs with fuel wires, I seem to average around 12.5 so seemed reasonable confirmation bias of what I thought I read somewhere.
Also - "Ideal but Safe" were my words. IF I read the target is 12.5, they did not say it in that way. I just implied that as a rationale for why they chose to target 12.5.
I was not able to find where he/they ever specified an actual AFR, the logs they posted with fuel wires and testing them out and the corresponding dyno runs look to be about 12.0. mine was also always about 12.0 with the FW and trims not maxed.

I believe stock targets low 11 to mid 11s at WOT, FW to add half a point to lean it out to about 11.8-12.2 would be reasonable. going leaner by a full point or more from stock especially with adding a bunch of additional boost on top would not be advisable in my opinion.

Lower RPM and initial throttle will be leaner, but by about 4500-redline it should be stable.

How much boost you are running / adding would also impact as well as what octane. 93 non red sport on map 1 would probably be fine at 12.5, a custom map 6 with +7-8 psi peak not so much in my opinion, and even more so with lower octane.

Here is a link to the parameters, although this isn't specific to VR30s it is for the N54 platform so not 100% accurate or not all of the parameters are actually used.
For example AVG IGN is not used on our cars. I would not reference the actual "targets" from this sheet to apply to the VR30 either, a general description of the parameter though should apply for most.

Your 12.5 avg afr, is that avg from 4500-redline,? is that with trims maxed? and how much boost?
 

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IRSBlueRS really appreciate detailed explanations. I personally am not having this issue - just helping some others interpret their logs. Unfortunately the ones seeing the lean AFR values are not trying to lean out the AFR, their fuel pump just can't keep up at relative conservative boost levels of 15-16PSI. The timing on their logs look good so it is frustrating for them to have to back the boost back down due to running too lean.
For the guys who ae tuned...Burger is targeting 12.5 AFR with the JB4 fuel wires. What are the individualized tuners targeting when they are pushing out 18+ PSI boost on stock fuel pumps? What AFR is being achieved in the logs?
I would start with a can of Seafoam. Direct Injection injectors get clogged a lot sooner than MPI. You can start noticing it as soon as 10k miles.
 

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Discussion Starter · #15 ·
Yes avg 12.5 about 4300 up on the log I just looked at. Below that AFR was higher/leaner. Trims max out and back off during the pull - not just pegged on max/44. Example at 4650 RPM on this particular pull it was max and AFR was 13.0 so I assume the car was trying to richen the mix...later at 5200 RPM the AFR was 12.0 and Trims dropped all the way to 31 and continued dropping. AFR fluxed from 12.3 - 12.5 the rest of the pull (went to 5700 RPM in 4th so I was really moving for the road I was on). Trims kept dropping to 21 by the time I let up. Full throttle throughout.
 

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Discussion Starter · #16 ·
I would start with a can of Seafoam. Direct Injection injectors get clogged a lot sooner than MPI. You can start noticing it as soon as 10k miles.
1st Seafoam reference I remember seeing on this forum! Good point though...might explain why some are having trouble delivering enough fuel even at fairly conservative boost levels. May try some cleaner in mine because I think my AFR is creeping towards the leaner side now that I am looking closer at that parameter!
 

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1st Seafoam reference I remember seeing on this forum! Good point though...might explain why some are having trouble delivering enough fuel even at fairly conservative boost levels. May try some cleaner in mine because I think my AFR is creeping towards the leaner side now that I am looking closer at that parameter!
ill probably try seafoam. let me install fuel wires (posi taps come saturday) log a map 4 and 5 run and then do seafoam.

good experiment
 

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Lol. I'm not selling Seafoam or anything, it's just the only injector cleaner I've used that actually works.
 

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Lucas injector cleaner > seafoam injector cleaner

some threads on here about seafoam valve cleaner being decent but not doing much past a certain point/mileage and needing a walnut blast instead.
 

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Discussion Starter · #20 ·
Lucas > Sea Foam. What about Lucas vs Techron?
 
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