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 Post subject: Next Problem to be Cracked: Tip-In (Accelerator) Enrichment
PostPosted: Tue May 01, 2007 4:14 pm 
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I think the next problem we really need to crack open is the throttle tip-in enrichment with larger-than-stock injectors.

The problem here is that I think it is difficult to define with our current logging what is perfect tip-in (or as close as possible), and what is not-so-good tip-in. We also haven't rigorously defined what the purpose of the accelerator enrichment is. Is it simply to provide some necessary extra fuel until the MAF sensor begins to register the new flow? Wouldn't this mean that a larger TMIC or a FMIC with very long piping would require different amounts of time for the tip-in enrichment to be in effect?

I have spent quite a bit of time looking at my wideband logs (Innovate LC-1), and you can see some interesting things if you look at them in combination with logs of the short-term fuel trims. I have found that when the tip-in is very rich, the ECU appears to see this on throttle tip-in and compensate with a short-term trim that removes fuel. This happens extremely quickly, but in the end causes some weird oscillations in AFR when it should jump straight to the necessary AFR. If the tip-in is *extremely* rich the car will bog no matter what when you punch the accelerator. It will only hesitate slightly if the tip-in settings are slightly rich.

I haven't had the gonads yet to drop the tip-in down to ridiculous levels in order to see the effects when the fueling swings very lean.

It would be interesting to see what tip-in looks like without any fuel trims whatsoever. That might be the key to tuning it best - disable short-term and long-term fuel trims (ie always in open-loop), start off rich, and watch with a high-speed wideband logger (Innovate, etc) while tweaking the tip-in values until the AFRs turn out as perfect as possible. Then re-enable closed-loop fueling and go on with your life.

As I mentioned earlier, I also understand that FMIC users have issues with tip-in enrichment not extending out long enough in order to keep the car from spiking lean. In that case it might be helpful to be able to extend the time that the tip-in enrichment is in effect. This might also be useful for large TMIC users, although I imagine the order of magnitude of the effect is far less.


So then, I propose the following questions that should be answered and then integrated into the Wiki documentation:

#1) What is the full and proper definition and use of Accelerator Enrichment?

#2) How can we best determine the ideal Accelerator Enrichment given the proper tuning tools?

#3) Can we find a generic formula for determining a new Accelerator Enrichment given normal mods (larger injectors, etc)?

#4) Is there a problem with the Accelerator Enrichment as currently implemented in the firmware when a FMIC or larger TMIC is installed? If so, how can this best be resolvedwq?


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 Post subject:
PostPosted: Wed May 02, 2007 2:57 am 
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Joined: Mon Oct 23, 2006 2:57 am
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Location: Carol Stream, Illinois
i am more then willing to help anyway i can. I dropped my tip-in values and it seems that it has caused quite a low load flat spotting. I guess the biggest question is how the ECU checks the Tip-in values and applies them. I think that's the most important part to figure out.

Jeremy

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2001 Impreza RS w/ 2003 USDM WRX Swap
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 Post subject:
PostPosted: Thu May 03, 2007 1:58 pm 
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Location: Indianapolis, IN
Tip in throttle enrichment pops all four injectors a few times for a very brief period. The period is defined by the map. It seems the number of times it pops them on is always the same (I think four, off the top of my head).

You can HEAR it if you listen to your knock sensor with an audio hookup.

http://pw1.netcom.com/~bsundahl/knock/s ... Sounds.htm

Just go out and push the throttle in quickly varying amounts, look at your WB (maybe even stock WB) to make sure your fuel isn't going too lean or too rich.

You can log your throttle delta if it is in your log def to help make sure you touch the right spot on your map. Perhaps Merch can add this to the logger defs. The AJ243 is FFFFA570 (float). Only problem is the logger may miss an event so you so you might have to try a few times to get a good log of it. It seems pretty straight forward, though.

If the map row header is 10 at a given spot, that means the throttle value increased by 10% within the window of time alloted for checking throttle delta. So if you stab the throttle quickly and it changes by 10%, you see the car go lean, bump up the map at the 10% spot. If it goes too rich, lower the number. I also find larger injectors need the whole map scaled down by approximate the amount you changed the injector scalar.


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 Post subject:
PostPosted: Thu May 03, 2007 2:09 pm 
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Location: San Diego, CA
Great info Freon, that last post deserves a FAQ entry. :)

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 Post subject:
PostPosted: Thu May 03, 2007 2:27 pm 
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Freon wrote:
You can log your throttle delta if it is in your log def to help make sure you touch the right spot on your map. Perhaps Merch can add this to the logger defs. The AJ243 is FFFFA570 (float). Only problem is the logger may miss an event so you so you might have to try a few times to get a good log of it. It seems pretty straight forward, though.

I can add this. I've logged it before on my 02 wrx. I can confirm on my car that it does require that you minimize the number of logged parameters or you won't get enough resolution for it to be useful. I can also add the post-compensation (boost error, ect, etc.) target enrichment. There is also a minimum enrichment value in both ecus which I think Freon mentioned before for which no enrichment will be used if the target enrichment is below this value.


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 Post subject:
PostPosted: Thu May 03, 2007 2:58 pm 
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Well, none of the enrichment stuff applies to the throttle tip-in. It is a different system that fires all four injectors together regardless of primary fueling. I'm not sure if you're just mentioning the enrichment stuff as an aside.

If you listen to the audio clip of accel enrichment at the link I posted above it will make more sense. The throttle tip-in enrichment map we're talking about doesn't actually go into the injector pulse width or fuel enrichment stuff that you might talk about otherwise.

I.e. this map works even in closed loop. It's actually hard to avoid it. You have to push the throttle in *very* slowly to keep it from kicking in. I think the period it checks throttle delta is probably about 10hz, and I've found it is hard to get it to activate more than about 2 times per second. If it fires off once, it seems like there is a delay period before it is allowed to fire off again.

I think there is probably a watchdog thread that watches the output value of the map. The map is checked as a normal thread on a periodic schedule, constantly updating the value. If the value is not zero when the watchdog is run, it triggers a special routine to buzz the injectors the appropriate amount, then starts a countdown timer so it cannot be triggered again for 1/2 second or so. This is just from experience logging and listening to the buzzing. I haven't bothered trying to look at it in detail in disassembly because I don't feel there is a need.


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 Post subject:
PostPosted: Thu May 03, 2007 3:33 pm 
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Freon wrote:
Well, none of the enrichment stuff applies to the throttle tip-in. It is a different system that fires all four injectors together regardless of primary fueling. I'm not sure if you're just mentioning the enrichment stuff as an aside.

The enrichment compensation tables (boost error, coolant temp, etc) compensate the tip-in target. That is, if the tip-in target was 1000 and the boost error compensation multiplier was .5 (-50%), then the final tip-in target would be 500.

The one thing that seemingly didn't make sense to me before you mentioned the "popping" of the injectors - it was obvious in the code that tip-in "enrichment" does not compensate the current IPW, but rather overrides the current IPW regardless, but it does use injector latency. So, perhaps enrichment isn't the best description for these tables.


Last edited by merchgod on Thu May 03, 2007 5:43 pm, edited 1 time in total.

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 Post subject:
PostPosted: Thu May 03, 2007 4:43 pm 
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Location: Sacramento, CA
Does that mean if my boost error table is 0 ( <--Cobb ProTUNER value) I will have no tip-in adjustment?

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 Post subject:
PostPosted: Thu May 03, 2007 4:47 pm 
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What about the 0% TPS delta column. How does that play into the injector 'poping' sequence?

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 Post subject:
PostPosted: Thu May 03, 2007 5:38 pm 
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Double Phister wrote:
Does that mean if my boost error table is 0 ( <--Cobb ProTUNER value) I will have no tip-in adjustment?

Without knowing what units Cobb is representing it in, it is hard to say. With RomRaider, -100% compensation with the boost error table would mean no tip-in enrichment. Basically if the compensation drops the value below the minimum threshold (ex. 280 06 wrx) then the tip-in enrichment would be skipped.

Also this enrichment isn't active until tip-in exceeds a minimum value (ex .5% 06 wrx). So, the zero value in the table is simply there for interpolation between .5% and 1.0%. There are also other conditions which would skip over tip-in enrichment, although I haven't looked into this much.


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 Post subject:
PostPosted: Thu May 03, 2007 6:26 pm 
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Hmmm... Maybe I'll zero out the tip in table and see if it's still drives the same.

Cobb 0 is RomRaider -100%

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 Post subject:
PostPosted: Mon May 07, 2007 6:35 pm 
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Joined: Mon Oct 23, 2006 2:57 am
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Location: Carol Stream, Illinois
allright well today I had to go back thru and add another 10% back in due to some MAJOR tip in knock/lean spots. Drove the car to work and the IAM was at 16 and my tip-in knock and flat spot were nowhere to be found.

For reference my off idle tip-in was registering a -12 degree knock correction thanks to the new warm weather.

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2001 Impreza RS w/ 2003 USDM WRX Swap
VF-23, TXS Turboback, Hyperflow Top Mount, Modded Stock Injectors, Warlbro Fuel Pump


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 Post subject:
PostPosted: Wed May 09, 2007 8:18 am 
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FWIW I have an 02 wrx with modded stockers and was having problems establishing a stable ltft due to the car running rich on closed loop acceleration despite numerours tweaks to scaler/latency and maf. I actually ended up zeroing out the entire tip in table as an experiment and it has corrected the issue and the car runs fine (I have checked using my LC-1).


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 Post subject:
PostPosted: Thu May 10, 2007 11:23 am 
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I am currently tuning Deatschwerks 1150's on a built USDM Longblock (with a 02 wrx manifold of course) using an 03 WRX ecm not using my AVCS. I am using my ecm for my 0 load and my UTEC for Speed Density.

I have a blow-through on my FMIC close to my intake manifold, so scaling maf was a must and tedious, but my 0 load LT's are between -1.25 to 0. I kept the stock latency and put 1150 in the flow table. I feel their are alot of things that might rely on those values than we know of.

Tipin has been a real pain. At low speed ie traffice it really screws with me. I used a multiple of .37 on tipin and it still shoots rich. I am going to try going all zero.

My theory is the closer your MAF is to the Intake Manifold the less enrichment you need. Injector size can be a factor too, but I looked at some COBB tipin values for the lower output Deatschwerks injectors using stock intake setup, and they only pulled a little fuel later on in the table.

Again I am only using my ECM for cruise, because of my noisy built engine, so Props to you guys tuning the whole fuel table.


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 Post subject:
PostPosted: Thu May 10, 2007 5:28 pm 
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To add more info to this thread: I was looking at how the tip-in value is calculated by the 16bit ecus and it is actually quite simple. When the tip-in value is calculated, the current throttle position is stored. So, when it is executed again:
tip-in = current throttle position - last throttle position

So, the time element is very small (the time between each execution of this code). As such, it is very hard to get a decent amount of enough resolution when logging the tip-in%. I'm still going to add this parameter to a future logger release. Also, the current conversion for tip-in% in the ecu definitions (16bit ecus only) is off somewhat which I'll correct in the next update.


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