When should/does one need to enrich the fuel while on boost? To what target AFR while on light boost? 11 or 12 ?
Trying to track down my never ending knocking problem while on boost. Data logged the knock count, MAP and wideband parameters (about 6-7 entries a second). It appears that by 5-7 PSI, the AFR is still around 14 -- is that too late to enrich the fuel? By 8+ PSI, AFRs drop down to the 10-11 range (or lower if my Octane Factor is below 25%).
On a hunch, I went and increased the fuel trim cell #4 from umm 2% to 8%, increased octane factor from 0 to 50% and then went to get food. It appears to have helped / fixed the latent fuel addition / low AFRs. Yet on the drive back (engine off/on again), it appears to have reverted itself and back to its bad ways. Once I was parked, checked fuel cell #4 and it was 5.5%.
Is this an good indication that the Revtronix chip needs some reprogramming for more fuel earlier? Looking over a massive data logging thread @ nasioc, it appears that most tuned cars are already in the 12 AFR range by 1-3 PSI.
Legacy777 wrote:Can you put RPM & MAF in there so we have an indication of engine load.
Sure. But then logging 4 parameters is going to reduce it to ~2-3 entries a second, which IMO isn't going to give the granularity to see the transition changes/jumps and the problem.
93forestpearl wrote:Looks like you need better logging or something that is user tunable.
Yea, well the Subaru SSMI protocol sucks for speed -- 1953 baud. Unless one has an ECU replacement, there is no other way to data log any faster.
ericm: The stage 2 v1 chip worked just fine in my TW for months after the ECU learned everything. octane factor was always at 100% and WOT through the gears was a solid 11.5 AFR. That too was a TD04 tune running with my TD05.
Anyways back to the topic at hand...
When does fuel enrichment need to occur when getting on boost and to what level?
It's all going to depend on what your motor can get away with. Some are more knock prone than others.
I usually started to taper down at around 2-3 psi. My setup was perfectly happy with that, but it is going to vary by rpm and when you actually start making that boost. Where it is in relation to peak VE also makes it different. 3 psi at 2500 rpm is not the same as 3 psi at 5000 rpm.
ericem: the engine from the TW went into the SS. Sadly, revscan didn't expose the various fuel tables back then so I have no idea what the TW was at for comparison.
Legacy777: Alrighty, got some more logs with rpm and the MAF. Once again, at the start of my drive I changed fuel cell #4 from 5.5% to 7.8%, which appears to help drop AFR earlier while on boost... but after a while the ECU un-learns it. Examples:
Can you try unplugging the o2 sensor and seeing how the fuel trims adjust. I am still thinking the o2 sensor was possibly damaged when you transfered from the tw to the SS.
1993 Subaru Legacy L AWD Wagon R.I.P
1994 Subaru Legacy SS R.I.P :(
2004 Nissan Titan LE 4X4
2007 Subaru Legacy GT :)
93forestpearl wrote:I see some lean spots in your fuel map. There are several 15.xx : 1 areas. I'd take a look at fixing those, and the see what happens.
What are your intake temps (after the turbo) at those boost levels?
those 15 spots are at like 2 psi(except for the 5th gear pull at almost 4psi), is it really that critical at low pressure? 15 does seem kinda lean but you wouldnt need 11:1 at 2 psi would you? would EGT be better for tuning for stuff like this? what is the boost level when you want full enrichment?
I'm going to pull my AFR/boost readings with revscan and see what I come up with on a bone stock setup.
206er wrote:those 15 spots are at like 2 psi(except for the 5th gear pull at almost 4psi), is it really that critical at low pressure? 15 does seem kinda lean but you wouldnt need 11:1 at 2 psi would you?
On other logging runs, I'm often getting a wave of knocking 0.5 to 1 second after going WOT. I'm thinking that due to the slow logging interval and time for the sensor to "ring" that the high AFR during that transition time is a problem. Also the fact manually altering the fuel table seems to reduce the knocking at least for a bit until the ECU unlearns things. Heck twice now, the Octane Factor has increased automatically for a bit, after increasing the fuel table cell #4. Normally it never learns and instead, always decreases itself after I artificially raise it.
Additionally, going over that giant nasioc thread with peoples raw data logs from runs, they're pretty much all enriching by a few PSI. Surely by ~5 PSI they're all in the target AFR range for their tune/car. This also makes me think the tune on my stage 2 chip just isn't correct.
206er wrote:I'm going to pull my AFR/boost readings with revscan and see what I come up with on a bone stock setup.
I look forward to the numbers. You have the only wideband revscan now works with? luck dog. I'm back to using EvoScan (newly updated data.xml file too PLUS I got the evoscan developer to fix some connection bugs) for my data logging so I can get wideband numbers.
From looking at the numbers....it looks like you're going very rich after the ECU unlearns whatever you changed.
I'd say try starting around 13 at 0 boost, taper to 12 around 3-4, 11.5 around 6, and 11 from there on out.
As Dan mentioned, each engine is different. Those numbers I gave are kind of respective of what seems to be working on my engine. You may find that you need to richen things up a little. So just use that as a guide.
Grrr, I must not be getting the whole picture into the various fuel tables / other parameters in the ECU with Revscan. Fuel cells (via revscan) look basically the same as before. More logging on the drive to work and its the same old story -- octane factor in the 0 to 12.5% range, staying WOT often results in a dropping AFR, etc.
Drive home, the ECU must've started to learn more because the vast majority of the time, it started to hit the target AFR of 11.5 while WOT. Hell, the octane factor even learned itself from 0 to 100% (and then over the drive reduced itself back down to 0% -- doh!). Same story as always though where its running lean up to 5-6 PSI and then drops the AFR down.
Example of a run where octane factor went from 50% to 100% (5th gear I recall).
At least another dozen examples of WOT runs with no/little knocking, mostly solid 11.5 AFR from tonight. This just doesn't make any sense. I haven't changed anything!
Can you give me a quick recap on the issue? Is it that the ECU is changing stuff without rhyme or reason? Or is it that it is consistantly lean at low boost levels? Or something completely different?
