Lexus maf question

[moorman]

There's quite a bit to address here....I'm sure the forum will time me out before I finish my response <opens notepad>. (that's my petty bitch for the day)

Ok.....

moorman, how sure are you that you have the correct afm?

Absolutely sure, part# 22250-50010.

because according to my calculations

Bah! Calculations! ....where are they when you have two cars with identical setups yet they turn out different results? At one point during my build/tune phase, I kept hitting FC at moderate boost levels so I backed out the bypass screw quite a bit. Turns out I had a nice slit in one of my couplings. I replaced the coupling, but never bothered to readjust the screw. The resulting bonus is that I've run 25psi w/o hitting fuel cut.

using 40psi as base pressure, youre getting about 12% more fuel by bumping to 50psi. the lex maf is supposed to be 25% bigger and you still trimmed fuel another 18%.

Those percentages aren't cumulative, as the S-AFC is only adjusting the AFM signal by 18%, not the total airflow or the total fuel. Despite that, we get back to my 'calculations' comment. Perhaps the 440s I have have been rebuilt, maybe they flow more than 440cc @whateverpsithey'reratedat. If all remained equal and proper according to calculations, those who install the Lex AFM & 550's at the same time should have identical AFR's as stock....yet I've read of many (on the SOGI list back when I was researching for my 1st MkIII) running -22% on the S-AFC. 25% more air, 25% bigger injectors, yet -22% to get good WOT AFR. Once I started reading results like that is when I gave up on calcs, at least besides getting me in the ballpark.

btw, are you sure the second is the best tune? 13:1afr at peak torque sounds on the lean side

Absolutely sure. I don't trust AFR's collected after the cat, as they are on the dyno chart. That's why I posted my wideband logs along with it. In the software, you move the cursor (vertical white line) to see the values at the point falling under the white line....which makes it difficult to just take a screen-cap, as you only see 1 value. Here's the screen-cap for that run at torque peak.

about the safc, you dont have to change anything in closed loop. only make adjustments in the hi throttle map where it matters.

If you intend to attempt running the Lex AFM with 440's and without bumping up the fuel pressure, you will need to make adjustments for closed loop, or else you will be outside of the ECU's compensation range. I think attempting this would be a bad idea and not worth the effort at all.

The less adjustments you make at a time, the easier it is to get consistent results. K.I.S.S. What I did was (I'm omitting a little trial and error because I didn't initially K.I.S.S.), install Lex AFM, then adjust fuel pressure until my Vf signal was mostly in the middle of it's range while steady-state cruising. Only then did I move on to adjusting the S-AFC for WOT tuning. The wideband made this part easy.

this sounds too easy, anyone want to chime in and explain why this cant be done or isnt recommended.

Compensating for the Lex AFM via S-AFC alone would be far from easy, and would require constantly dicking w/ settings since conditions change constantly (air temp, humidity, pressure). I'd much rather match the fuel to the air in such a way as to let the ECU handle it natively, and only step in with corrections on a small corner of the map.


Whew....hopefully that all makes sense.

 

[shaeff]

read here. learn what you're doing, and how it works, BEFORE you do it
after you've read it in it's entirety, read it again.

http://rob.carlile.home.mchsi.com/lexus/lexus1.htm

-shaeff

 

[diy guy]

btw if you have a safc couldnt you just trim more fuel to trick the ecu into thinking theres less airflow instead of getting a bigger afm?

Really, I sure it's possible, (if I'm understanding this part of your post correctly) but I wouldn't. Since all the Lex AFM does is tell the ECU there's less air than the engine is really receiving, the AFC can do the same by modifying the signal -BUT- I'd rather not attempt to modify the closed-loop range since it's too easy to end up battling the ECU

about the safc, you dont have to change anything in closed loop. only make adjustments in the hi throttle map where it matters. you're not going make full boost, and therefore not hit fuel cut at part throttle anyways.

i was still following on that. safc+stock injectors+stock afm. car would function like stock until you went into the high throttle map, set at say 75% TP, where fuel would be trimmed to fix afr and automatically bump fuel cut. this conforms to your k.i.s.s. method

i used rc engineerings formula to calculate flow after pressure change, but you're right, calculations arent necessarily right. it still surprises me that you had to trim fuel at all with the lex maf and what are supposed to be stock flow injectors.

oh, and sorry, about not looking at the logs, i was just basing off the dyno. our of curiosity, what's the user1 parameter logging?

 

[moorman]

i was still following on that. safc+stock injectors+stock afm. car would function like stock until you went into the high throttle map, set at say 75% TP, where fuel would be trimmed to fix afr and automatically bump fuel cut. this conforms to your k.i.s.s. method

Ahh, ok. I'm not sure where FC would be moved to, but it has to change some.

oh, and sorry, about not looking at the logs, i was just basing off the dyno. our of curiosity, what's the user1 parameter logging?

user1 = Vf