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Old 04-29-2015, 12:22 PM   #1
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Default Req Fuel Calculator acting all weird

I've got a buddy who got a killer deal on a supercharger kit. It came with a rev build MS3 basic, which I've been helping him get up and running.

We're doing the "recommended" workflow of - 1) Install MS and tune, 2) install injectors and re-tune, 3) install boost and re-tune

We're on step 2 right now, and we have some questions:

Basically, we tuned with stock injectors, car fired up perfectly and the fuel map seemed almost perfect right off the bat (reverant, you seriously rock). Well, he installed the other injectors (525cc, part number 17113738) and adjusted req fuel per the calculator and changed his constants, and the car basically wouldn't start.

It finally fired up and it was running hella lean, so I did some quick maths and we re-calculated req fuel based on like 430cc injectors or something, and it idled pretty good. It seems the whole map is now good..

The biggest question is: is there something "wrong" with having a req fuel other than what the calculator says it should be?

I did some digging into all of this and I found the equation MS uses PW = DT + (ReqFuel * MAP * VE[RPM,MAP] * AirDen * BaroCor * corrections) which makes me think maybe the issue is related to deadtime...

So tl;dr:

If he runs a 525cc injector, is there anything "wrong" with using a fake req fuel based on like ~430cc?

What are some reasons this may be the case?

Are his injectors bunk?

Is his req fuel all fucky?

Is there some other constant we're missing or something that could cause this?
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Old 04-29-2015, 12:30 PM   #2
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No there's nothing really wrong with that. Had the same issue with some FICs I've used lately. And yes, injector dead times are a big factor. Personally I'd input the correct ones, adjust req_fuel so it idles well, then do a little auto tuning with a known good wideband (non-AEM), then visit the dyno to verify proper fueling, the tune for power with ignition.
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Old 04-29-2015, 12:43 PM   #3
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Originally Posted by curly View Post
No there's nothing really wrong with that. Had the same issue with some FICs I've used lately. And yes, injector dead times are a big factor. Personally I'd input the correct ones, adjust req_fuel so it idles well, then do a little auto tuning with a known good wideband (non-AEM), then visit the dyno to verify proper fueling, the tune for power with ignition.
Right on. I figured we could try to find the DT with the googles, and then go from there--but just wanted to make sure that there's nothing wrong with a "fake" req fuel.

Sounds like we're good to go, as long as AFR looks good?

EDIT: is hate for AEM back on?
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Old 04-29-2015, 12:45 PM   #4
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I always adjust req_fuel so that the largest values in my VE table after tuning are in the low 200s (255 is the maximum). That way, I get the most resolution possible out of the VE table.

There's no other magic to req_fuel. It's just a number that is used like you've shown in your equation. The calculators you get in the tuning programs are conservative. The main thing you want to avoid is a req_fuel that is too small and makes the VE table cells peg at 255.
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Old 04-29-2015, 12:48 PM   #5
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You gotta adjust the VE map for different injectors, it's not just a matter of flipping the req_fuel even though many make it sound like that's all there is to it. And yeah, dead times have to be on point too.

Basically change req_fuel to what it should be per the calculations. Adjust the rest as needed.

*edit: these guys beat me to it cause I'm slow at posting lol
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Old 04-29-2015, 01:25 PM   #6
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Originally Posted by 18psi View Post
Basically change req_fuel to what it should be per the calculations. Adjust the rest as needed.
That's what I did when I threw my 460cc red tops in, and it worked great, but for him, we had a near perfect fuel map with stock injectors, threw in new injectors, changed req fuel, and the entire map was ~30% lean.

I figured just changing req fuel to make things give 30% more fuel was easier than re-tuning the entire map manually, although I suppose a Select all > * 1.3 would work also.

---

So, for the workflow of getting req fuel such that VE nears low 200s (eg 230), basically you go:

1) 230 / (highest VE table value) = multiplier
2) Select whole VE table and multiply by multiplier (largest value should now be 230)
3) Divide req fuel by multiplier, this will make req fuel smaller.

Since our equation now is:

PW = DT + (ReqFuel * [Multiplier] * MAP * VE[RPM,MAP] / [Multiplier] * AirDen * BaroCor * corrections)

So the * mult and / mult cancel out, we inject the same amount of fuel, but we have greater resolution in our VE table..?
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Old 04-29-2015, 01:33 PM   #7
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EV1 injectors require higher than normal VE% values in the fuel table.

example: if your shitty Rx7 injectors were running at 35%VE at idle, your new injectors might want 65%VE if you scale the REQ_Fuel value correctly and then significantly reduce the deadtimes.
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Old 04-29-2015, 01:38 PM   #8
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Quote:
Originally Posted by curly View Post
then do a little auto tuning with a known good wideband (non-AEM)
Why non-AEM? Not trolling, genuinely curious.
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Old 04-29-2015, 01:41 PM   #9
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Quote:
Originally Posted by mlev View Post
So, for the workflow of getting req fuel such that VE nears low 200s (eg 230), basically you go:

1) 230 / (highest VE table value) = multiplier
2) Select whole VE table and multiply by multiplier (largest value should now be 230)
3) Divide req fuel by multiplier, this will make req fuel smaller.

Since our equation now is:

PW = DT + (ReqFuel * [Multiplier] * MAP * VE[RPM,MAP] / [Multiplier] * AirDen * BaroCor * corrections)

So the * mult and / mult cancel out, we inject the same amount of fuel, but we have greater resolution in our VE table..?
That's correct. But this final adjustment is like the icing on the cake and should be done after you've already got a fairly decent fuel tune. So, for new injectors:

1. Adjust req_fuel by the ratio of the injector volumes as has been described in countless threads.
2. Adjust dead time.
3. Tune fuel . . . always tune fuel when you've changed something.
4. Look at the resulting VE table. If the peak values are in the low 100s (i've seen this a lot), then you are giving up a full bit of resolution (7-bit maximum is 127). So you can benefit by doing one additional req_fuel adjustment. Make that adjustment exactly as you described above.
5. Now tune fuel again. Since you are using bigger numbers, each digit change represents a finer increment and you can get it just that much better.

I always autotune BTW. Why are you manually changing the VE map? Are you not able to use autotune for some reason.
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Old 04-29-2015, 01:41 PM   #10
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old injector size / new injector size
then multiply req fuel by that number
then adjust the VE table as needed

Quote:
2. If you know what your new dead time is, adjust that too.
This part is mandatory...not if
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Old 04-29-2015, 01:43 PM   #11
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Quote:
Originally Posted by hornetball View Post
That's correct. But this final adjustment is like the icing on the cake and should be done after you've already got a fairly decent fuel tune. So, for new injectors:

1. Adjust req_fuel by the ratio of the injector volumes as has been described in countless threads.
2. If you know what your new dead time is, adjust that too.
3. Tune fuel . . . always tune fuel when you've changed something.
4. Look at the resulting VE table. If the peak values are in the low 100s (i've seen this a lot), then you are giving up a full bit of resolution (7-bit maximum is 127). So you can benefit by doing one additional req_fuel adjustment. Make that adjustment exactly as you described above.
5. Now tune fuel again. Since you are using bigger numbers, each digit change represents a finer increment and you can get it just that much better.

I always autotune BTW. Why are you manually changing the VE map? Are you not able to use autotune for some reason.
Right, icing on the cake, you wouldn't want to do that to a fresh table, but just wanted to make sure I understood the process correctly for my own benefit later on.
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Old 04-30-2015, 12:17 AM   #12
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did some googles, found deadtime to be 1.2, punched that in, rerererecalculated req fuel based on real numbers, idle and map spot on.
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Old 04-30-2015, 10:09 AM   #13
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Quote:
Originally Posted by EO2K View Post
Why non-AEM? Not trolling, genuinely curious.
Love the product, but the more cars I dyno with uegos, the more I realize they display about 1-2 full points lean. So when I auto tune with them on the street, and visit the dyno, my tune is 1-2 rich.
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Old 04-30-2015, 11:10 AM   #14
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Quote:
Originally Posted by curly View Post
Love the product, but the more cars I dyno with uegos, the more I realize they display about 1-2 full points lean. So when I auto tune with them on the street, and visit the dyno, my tune is 1-2 rich.
Huh? 2 points? You mean like 12.5 is displayed as 12.7? Or like 12.5 is displayed as 14.5!?! Hopefully the former.
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Old 04-30-2015, 03:13 PM   #15
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Huh? 2 points? You mean like 12.5 is displayed as 12.7? Or like 12.5 is displayed as 14.5!?! Hopefully the former.
I'm guessing 12.5 on the AEM is 14.5 at the tailpipe... discovered this with mine during a test/tune session at the drag strip.
Not sure what's going on. Key on/engine off, idle, normal around town comparisons between the Tuner Studio values and AEM UEGO values are within a tenth or two of a point.

However, when logging full throttle runs through 1st, 2nd, and 3rd, they were showing up almost two points leaner in TS.
Tuned to the desired TS values of 13.2 and the AEM UEGO reads 11.2 in the car at WOT.

My last dyno with the AEM UEGO at 13.2 to 13.5 were showing about a half to a point leaner at the tailpipe that what the dyno operator is comfortable with.
Eventually I'll need to get the thing on a known good dyno and spend some time trying to tweak the AFR voltages in TS so that they end up being closer to what the sniffer says they are... or something. Not to mention turning off all of the MS AIDS (02 control, etc) that I just now realize could be contributing to the vast differences between around town driving and WOT activity.
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Old 04-30-2015, 03:18 PM   #16
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This is perchance a silly question, but was that tailpipe sniffer after a cat?

That seems like a pretty extreme disparity, and I cant imagine AEM would still be in business if it was the case.
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Old 04-30-2015, 03:25 PM   #17
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The cat thing I've heard about, but it still won't result in that much of a difference.

And yes, I agree on that last part: if all AEM's read that way they would not be in business
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Old 04-30-2015, 03:53 PM   #18
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No cat on the car... I'm chalking my particular issues up to user/installation/configuration error, rather than a faulty gauge.

Most likely my calibration on the AFR tables are off. Time to get it on a dyno and check things.
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Old 04-30-2015, 05:43 PM   #19
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Originally Posted by SchmoozerJoe View Post
No cat on the car... I'm chalking my particular issues up to user/installation/configuration error, rather than a faulty gauge.

Most likely my calibration on the AFR tables are off. Time to get it on a dyno and check things.
I do wish the pre-configured calibration tables (or even the ones from AEM/Innovate) were more accurate. Because they haven't been accurate on any of my installs.
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Old 04-30-2015, 05:47 PM   #20
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IMO, They really can't be too accurate, because every car has different grounds, conections, etc. that you have to compensate for with the calibration.

If you want accurate, get the CAN module from Rev and run serial. win/win/win. no guesswork, only win
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