Need help with understanding MAF adjustments.

Quote:

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Originally Posted by Redline Motorsports

Chuck,

One thing to consider is that when making changes like a CAI to a "factory" calibrated air system, its not just the increase of air that effects the MAF's but also the change in airflow through the MAF has changed. Maybe more so with the new style MAF....

I think the other issue is the coefficients that are used for fuel computation in the E38/E67 process. More factors are used in the final calculation that we forget have an impact.

I agree with the "make it work" method sometimes!

HT

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No doubt...I've considered that....But, I realize we've altered not just the MASS or VOLUME but, the flow characteristics....

Eventhough, it still should be as simple as we've added MORE air and with that the trims should reflect it by turning positive...

Another thought is that while we've obviously added more air (especially at WOT) but, maybe we've significantly added more WOT air, but with the larger more efficient flow potential, we've actually lost velocity in the idle areas resulting in slower air or that the meter just isn't efficient at the lowest air flow rates resulting in the negative trims???

Make sense to anyone?
Chuck CoW

I have been doing a maf only tune on my race car. I am bypassing the ve table to where anything over 400 rpm's is maf derived.
I went to the track and it was way lean with just maf tune in stock form. Injectors were scaled using marcin's spread sheet. I have 30 lb/hr redtop injectos .
When i first made a pass at the track ,(no dyno yet) my car was lean. WOT read around 14.2/1 which I only made a partial run to watch the log.
Instead of dicking with the table , I hooked up my old mass air flow translater and set it at 14% rich for wot and 10% pt. Went back and logged it, 10.2/1 air fuel at wot.

I pulled it back to 8% rich and the air fuel ratio went to 12.2- 13.2/1 in that range through out the rpm range.

the problem is that my maf was reading almost 11,000 htz and my timing went down from a commanded 26deg to a whopping 2.5-6 degrees at wot . It showed 1.2 deg of knock when I first started into the throttle but then the knock went away. as soon as I went to wot is when the timing went way down to the single digits.

Last night I took the Maft off and scaled the injectors -3% to see what it would do with the timing and launched the car in my driveway( neighbors love me) . ON the log, my timing bounced between 24 down to 16.5 and back up to 24 with 0 knock.

Air fuel went to 14.1 again , I was thinking that I need to drop the injectors down a little more to see if that helps.

I am a little on the lean side through out the tune idle all the way up the rpm range , I command 14.63 at idle and it see's 16.5/1 up and down a little from there. I command 12.0/1 at wot (starting on the safe side) and am seeing 14/1.

I tried to do a auto ve tune first and no matter what I tried the car was so lean that it would not idle. I added the 15% to the ve table and it just wont stay running and when I touch the throttle , it bogs down and dies.

THis is why I started fooling with the maf tuneing. Less tables to fool with and changes with the weather.

I would not fool with injector flow rate on my Trans am that I drive, my race car is Idleing great and doesn not stall or surge when I come from high rpm back to idle with the maf only tune in it.


Am I completely wrong in thinking of playing with the inj. flow rate to get it in the air fuel that I want?

Aint Skeered,

Do what works for you...

there may be something going on that is not immediately apparent (maybe we need to look at your tune/logs again to figure it out).

Also do keep in mind that a racecar is different than a daily driver...

the racecar spends 95% of its time at idle or WOT, whereas the daily driver spends 95% of its time at idle or part throttle...

however, having all the tables correct has the following benefits (for both racecar and DD'r):
- part throttle driveability/repsonse of the the daily driver is better/improved (tip in, tip out, cruise, coast, ...),
- WOT AFR's are easier to set (what you edit in B3618/B3605/B3647 is the actual output AFR you see),

The tables all work together... so there are many combinations of values that will produce desired results in most cases...

...but if that is not working, then do what works... tweaking the IFR is not necessarily wrong, it is another method.

Cheers
Joe
:)

Aint Skeered-- and anyone else who's listening--

As joecar has noted, "Do what works for you". There are all kinds of theories about tuning-- some are right, some are wrong and some are both, depending on the situation. The philosophical problem I have with altering IFR is that it's the one variable that you can tie to an actual known value. On the other hand, I haven't found conversion factors to be all that accurate, and I'm pretty sure that some of the factory IFRs have a fudge factor built in. As an example, I have a set of LS2 injectors installed in a 5.3-liter truck engine. With the stock injectors, fuel trims were in the 0 to -4% range. Afer installing the new injectors and changing the IFR table, fuel trims were positive 10%. Fuel rail pressure is the same as test pressure, nothing else was changed, so the only thing that made sense was to change IFR.

Something else to consider-- on the old mass air systems, altering IFR was the only viable option because these systems didn't have a VE table and working through the mass air calibration tables was a painfully slow process. I've done a lot of chips for these cars using changes in IFR to dial in air/fuel ratios and gotten the results I was after.

In spite of all the theories and explanations, if wide band readings and commanded AFR are the same, it doesn't get any better than that. Someone can tell you that everything you're doing is wrong, but if the results are right, that's all that matters. Just be sure to keep accurate notes so that a month from now, you'll know what you did and why.

Thanks Guy's. I am dropping my ifr a total of 6% and I added 20% to my voltage correction table . I am going to try that Wensday night at the track to see if it puts me close. I also set my pe to command 1.22 eq to start. I am going to keep modding my Ifr untill I get air fuel to match commanded and then start reducing the fuel in pe.



I do have a little stumble on tip in , I guess that is going into pe mode. Any suggestions on getting that out? I only have the log of a short launch in my drive way with the tune that is in it now, Also can you see why on my log the timing at wot goes to 24 then down to 16.5 and back to 24?

Oh yeah, on the few cars that I do tuning on I save every tune with a discription. The files add up but untill I get one I am happy with , I save them before I change them.

The log is of the tune with -3% on fuel injectors.
The -6% is what I am going to load and try out.


Just so you know what I have for an engine and trans. It is a 347 with 11.63 /1 compression, cam is 239/243 at .050 with .612 lift int. .610 lift exh 112lsa 110 icl.
I have a truck intake with a 75 mm t/b that seems be not in need of porting. It is different then car t/b's and has a 3/16 th hole in the throttle body. It Idles really well as far as not surging but does seem to have a cleaner sound to it when it is closer to 14.7
When it is close to 18 /1 it still idles but it is not a clean lope.
Trans is a th350 with a 8" converter.

My timing is copied from my Trans AM which is a 6 spd. Will the th350 want a different timing table to hit the converter harder?

Quote:

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Originally Posted by dfe1

in spite of all the theories and explanations, if wide band readings and commanded afr are the same, it doesn't get any better than that. Someone can tell you that everything you're doing is wrong, but if the results are right, that's all that matters. Just be sure to keep accurate notes so that a month from now, you'll know what you did and why.

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+1.

Thanks Joe. I am sticking with this method for this car for a while to see how it responds at the track. I may try to fool with the ve tables if I ever get on a dyno but its to hard with out being able to drive the car on the street.

I have a friend with a 408 ls1 that he had tuned by a pro and that is what gave me the idea for maf tune. His car runs and drives perfect and its all maf. The tuner is use to doing fords and this is mostly how he has to do them from what he told me so he stuck with that method.
His car drives really good with no surging also.

I offer you another option (might get some flack for this - but oh well).

1-Disable VE by dropping MAF threshold from 4,000rpm to 200rpm.
2-Using WBO2, alter IFR table (down for more fuel - up for less) based on stock MAF curve (extend top end if necessary) and %AFR error. Rinse/repeat 2~3 times if necessary.
3-Unplug MAF and tune VE with newly developed IFR table.
4-Plug in MAF, restore 4,000rpm threshold and enjoy.

Now, timing won't shift grams/cylinder calculations from altered MAF tables. A4 trans pressure calcs too. Basically, anything that refers to MAF input for load calculation. :)

Or you can set your injectors, "Disable VE by dropping MAF threshold {B0120} from 4,000rpm to 200rpm" and use BEN against {B5001}.

this is easy with RTACS without RTACS i suggest increasing {B5001}
by X amount first so you don`t run overly lean.

after injectors are set and Auto VE, this is your best bet. IMO
"Auto MAF" :hihi:

Flack is not necessary... it will be interesting to see how close the IFR table gets. ;)