I just set my VE table to values close to 0 all over the RPM/loading band (Using HP Tuners). Now, when conncting the MAF, the LTFTs are all over plus 15 to plus 25.
Next step would be calibration of the MAF. the question is if it might be possible to just let the car run without MAF in SD. I could take the MAf out and replace it with a straight silicon tube being less restrictive than any MAF you could get (no sensors, no screens).
I use the WCC High Flow MAF without screens, and i think this unit is messing up my LTFTs like crazy.

What should i do to have the car run without MIL and in SD after removing the MAF?

How about the spark tables (high/low octane) ?
Should i set MAf fail freq. to "0" ?

What would be the benefits, negatives when driving in SD. I dont care for emmisions control, can change back to MAf in 10 Minutes . . .

Will the car produce more Power/Torque when staying in SD ?

Hope you guys can help . . .


Take care,

Jochen

 

If all is tuned right and running right, a MAF-less car isn't going to be any stronger than a MAF'd car. The downside to running without a MAF (from what I've read here) is the car's inability to compensate for environmental changes. So, you'd have to tune the car with some frequency to keep the tables in check. The aftermarket MAF is probably the source of your problems when it comes to your positive trims. I'd go the MAF recalibration route and see how it runs. With the Excel sheets available to help you dial it in, I can't think of a solid reason to run without a MAF. Just my .02

 

https://ls1tech.com/forums/showthrea...25#post2767425

Good VE/MAF info here.

 

Thank you guys.
I guess a proberly tuned maf will do its job as good as running in SD, But i drive the Corvette only in summertime, so why bother with calibrating the maf when the car runs great in SD and gets a few g/sec. more air without MAF Sensor ?

I realised that driving the car without MAf it seems to run more smooth, ne transition hesitation, no surging. I drove for the past 6 years with MAF and never realised that the car could run better without.

Jochen

 

The SD calc used by the PCM takes into account both IAT and MAP readings. So yes, SD mode does have the ability to compensate for environmental changes, outside of humidity. My trims for the tune I did in 40* weather are the same now in 80* weather.

Not coming down on you, SSpdDmon, but I'd really like to kill this misconception, because it keeps rearing it's ugly head.

 

It's not a complete misconception... Weather changes do make SD airmass calculations more fuzzy. Now you're one of those people that have not had ill effects of SD operation and I'm glad to hear it. I have heard of others who had the same problems as I. Either way you look at it, the MAF is still a much more stable airflow metering device. With the IAT and MAP not being steady, often times your airmass calcs are "real time" but could also be skewed due to sensor readings. The MAF could also have it's error margin as well, but it's one sensor vs two. There's nothing wrong with SD airmass since over time it's pretty much going to build an average anyway as far as trims learn but SD is much more sensitive and can be easier coerced into doing something stupid.

As per my own experience, a perfectly working SD tune at 70 degrees netted me super negative trims once in 40 degree weather and even verified with wideband when returning to open loop. Having made zero changes to the tune, commanding 13.0 in 40 degrees produce 11.0-11.5 on average, whereas at 70 degrees I was producing as commanding. This result has occured on a friend of mine's vehicle as well. After VE tuning and 13.0 WOT tuning on the dyno, we left the car in SD mode. A month later he did a dyno run for fun, lost 20 horses, ran a 12.4 A/F with no knock. Same dyno, same tune, different day and yes different temps/humidity. It wasn't just a dyno quirk either since he and I run dead even from a roll and later that afternoon I walked away from him pretty convincingly mutliple times. And YES I KNOW WHAT I'M DOING... I scanned his part throttle and he was running overly negative trimming, and when placed back in open loop, was on average producing 12.0 when 13.0 was commanded of the VE. This with trims reset out and all to verify it's consistency.

I wouldn't be so bold as to call this a misconception just yet!

 

You're right, the SD calc is not all knowing and all seeing. The MAF plus dynamic airflow filtering is also a much more precise and adaptable way of setting fueling than SD alone. However, the popular conception of SD operation is that it is blind to temperature and altitude (a statement I see oft repeated on this board), which is simply false. That's the misconception I want to put to rest.

 

my car is in SD and my MAF has been long gone, works great for me too. ive seen about a 50* swing in temps with no ill effects

 

also, based on calculations, the car would actually theoreticly run richer in hotter temps. so tx horns, i wonder why you got negative with colder temps? at least this is just what my professor said.

 

Great replies, thank you guys. I know there are different opinions and experiences (as with all discussion topics). I appreciate hearing both sights, SD and MAF calibration. Anyway, the SD tune has to be good as the MAF running needs the VE SD tune for transient fueling, so the VE tabel has to be correct.
I have to think what to do. Would like to get more input form guys who verified SD dyno runs compared with MAF running dyno runs . . .


Jochen

 

With Lambda control.. (i.e. AFR compensation with a wideband sensor) the SD becomes more appealing. While having a hard time compensating for what is going in... it can see what is coming out and adjust accordingly... granted it is not as quick but works none the less.

Its amazing what a hot wire flow meter (MAF) can do for quick compensations. I Run SD on my Formula open wheel racer but would also like to determine the inlet airflow... there are more ways of measruing inlet airflow... the MAF just happens to be quite simple and cheap.

 

TXhorns281 was a big fan of SD until we figured out how to set up the MAF right, and now you can have the nice power and throttle response of MAF without the PITA of SD's finnicky nature.

 

Thanks for dropping in, redhardsupra. I downloaded your MAFspreadsheet a while ago. I think this is a great xls file and many people are using it. My LTFTs are, after calibrating the VE tabel without MAF to almost all cells to "0", with the MAF well postive. Since they are all in the same range positive (plus 18 average), would it be OK to just increase MAF table by, lets say 10% and check again LTFT, or would you recommend using your xls file in any case ?

Thanks for your help.

Jochen

 

use the excel file.

 

umm..pardon my reading skills, but are they 0 or are they +18?
the whole idea is to have your MAF behave like SD, and that's what my spreadsheet does.
tune your car in SD as normal, but as you do that, also log for the two fields my spreadsheet needs, then just use all these data to create one big MAF calibration from a lot of sample points. if it's done right, your LTFT histogram should not change much at all when you go back from SD to MAF mode. That's the cool part.

 

When MAF is disconnected all LTFT are now around "0", some +/- 1 or 2. When i reconnect the MAF all LTFT go up again to average plus 18.

 

Well, theory and "what your professor" said isn't what happened for me and many others in the real world...

VE airmass is more prone to error period. I'm glad your car likes SD, but there's a reason it's the backup system and I'm sure GM engineers just gave us a MAF b/c it was a shittier system.

 

definitely need to rebuild your MAF airflow curve...

 

i know its not what happened to you, but what im saying is i wonder why it goes the otehr way

 

I see where you are coming from, yes temperature is MOST DEFINITELY a key element of SD tuning... lol That's is one of the main variables when determining the airmass. It's not that SD is blind to these things, it's that it takes these readings (whether false or not) and takes them too literally. And it is also slower in its reaction due to constant calculation as opposed to direct referencing. To us, this may seem like a negligable time lapse, but to your motor that can mean all the difference when deciding how to combust.

*****************

And the idea behind me running richer in colder weather is that with reduced air temps, we see a greater airmass value. And with cooler, denser air, you would expect to see higher MAP values. So in turn the PCM wants to match it with a higher amount of fuel. But what if the airflow that is determined by SD calcs is for whatever reason more than what the motor is really using/wants or maybe air temp and density aren't the only factors contributing to combustion. This could inturn overshoot and create rich conditions. Keep in mind b/w the IAT and MAP sensor there can be a large discrepancy in airmass calculations (for fueling purposes) since we're talking about a multivariable function now. How is this different from the MAF? Well, the MAF itself is a true measuring device whereas SD is more an expectation from less precise devices (in regards to direct airflow metering). And for heavier modded cars, airflow is a much more critical element to be accurate about as to keep fueling inline.

I ran without a MAF for a long time over the many faces of weather we see here in TX and it's not like some operator error thing that I'm running into. Tunes untouched, they have not remained stable for myself, or for others I have worked on. So from that, I go back to the MAF, get it dialed in as it's supposed to be, and have seen very stable fueling, great throttle response (which I will say that an untuned MAF will make SD throttle response feel like a godsend), and no loss in power as far as comparative racing goes against other owners.