God Forgives I Dont

Ok this maybe stupid or just impossible to do but...

When tuning the VE table we remove the MAF from the picture and assume that how ever far off the LTFT's are that the VE table needs to be adjusted by that amount to correct it.

So it would seem to me that there should be a way to force the PCM to never use the VE-SD calculations and to only use the MAF based calculations.

Then we could say that however far off the LTFT's were from 0 at a given MAF HZ then the MAF table for that HZ would need to be adjusted by x%?

If that makes any sense at all?

Is it even possible to force the PCM to only use the MAF by either changing some parameters or possibly unplugging a sensor some ware?

horist

makes sense... but GM didn't program the PCM like that (for good reasons too... the SD failover we use to tune in SD .. is just that... a failover... GM intended it as an effort to keep the car running in the event the MAF failed)

I don't think it's possible to force the PCM to use only the mAF right now ... the fact that we can disconnect the MAF and go into Speed Density is only because we are using the GM failover method in the PCM (failover incase the MAF fails)

God Forgives I Dont

But wait I've been reading in these threads many times over were people have stated that it’s blended as for which one the PCM chooses to use. It’s been said that if the MAF is hooked up and turned on the PCM will tend to use the VE-SD for lower RPM and all MAF for the upper RPM.

I can tell just by looking at my logs that the MAF is primary but my current understanding is the VE-SD is not a failover but being used in blended form.

So if the VE-SD is really just a fail over then all error can be associated to the MAF table being off? If that is true then it would be simple to correct it and the calculations that we are doing should be dead on accurate. But I've tried out all the MAF calculators and methods and had mixed results none of which have been really great.

Another_User

I have thought about this before. It may be too much of a PITA, but here are my thoughts:
1) you can probably eliminate SD calculations by making the MAP fail (unplug it, or fail it in the PCM, if possible)
2) if that works, the PCM MAY still try and do some n-alpha type calculations, which would mean you would have to fail the TPS sensor (same as MAP), this would prevent the PCM from making this type of calculation

Then, if your car will still run (because this has not been tested, but I would love for you to test it for us), it should be making it's calculations based entirely off of the MAF. Hope that gives you a good idea of where to start.

Silverhawk_02TA

The maf works great for measuring the airmass that is entering the engine... when it is doing so at a constant rate. When the amount of air entering the engine is changing, like during throttle transitions during normal driving, the maf is not at all accurate. This is where the VE table kicks in and supplies an airmass calculation to pick up where the maf is lagging. Aside from this, the VE table also serves as a reference that the PCM checks the maf signal against to ensure correct operation. So, you could have a maf table that is spot on, but if the VE table hasn't been adjusted as well, then the measured airmass isn't going to correspond with the calculated airmass. Worst case scenario, the VE table could be so far off that the PCM decides the maf is malfuntioning, at which point it'll throw a code and fall into SD mode. If it's not that far off, it'll just throw your trims out of whack as the PCM tries to adjust fueling during throttle transients based on incorrect VE values.

In other words, if the PCM is reading a steady MAP signal, or the RPM is over 4000, the fueling is set using the maf signal alone. If the engine is under 4000 RPM, and the PCM sees an unsteady MAP signal (like during throttle transitions), then the fueling is set by the maf signal, and then tweaked by the SD calculation derived from the values in the VE table.

Make sense?

txhorns281

iTrader: (12)

Could not have said it better myself!

crainholio

iTrader: (2)

GM did that on the TPI platform from 1985-1989. No MAP sensor, no VE tables, just a MAF sensor and airflow:voltage table.

God Forgives I Dont

So what I'm am gathering is that its imposible to take the VE table out of the picture? So take the MAF out and put it on the shelf because with it in the mix there is no garantee on anything. Is there any advantage to keeping the MAF that makes fighting the PCM and trying to make the MAF dead on accurate worth all the trouble?

Silverhawk_02TA

Yep. Learn to love the VE table because you are stuck with it.

But, let's not trash talk the maf too much. It does the job it was designed to do (measure steady airmass entering the engine) very well. Sure, it takes a little more work initially then going straight SD because you also have to scale the maf table, but with a maf you won't have to tweak the VE table for atmospheric changes. For example, I had my VE table pretty much set when I was in Washington. All my LTFT's were between +/- 3. Then I moved to New Mexico, and going from sea level to about 5000 feet sent my LTFT's to the +14 to +16 range because of the barometric pressure drop. Volumetric efficiency changes with altitude. Back to square one. Personally, I like the added control SD affords me, and I like tweaking the VE table. Some people would rather just set it and forget it. Just depends what you want.

Another_User

I would have thought going from sea level to 5000 feet would cause you to have negative trims. Hmmm.

txhorns281

iTrader: (12)

Well, you might want to run a MAF in order to keep your tune anchored and trims to not stray away from a good place. The MAF is much more independent in regards to weather/load changes. If you align the MAF and VE close enough, there will not be any stupid problems. The MAF will not adapt and learn, but the VE will so the two will never be in perfect harmony, but the closer together they are, the better your fueling will be AND YES IT CAN BE DONE!!!

P Mack

iTrader: (6)

Nobody has mentioned changing the high rpm disable from 4000 rpm to something like 1000 rpm yet. Of course i don't think anybody's tried it yet either. Either way, it's really not necessary to make your airmass calculation based entirely on the maf just to tune your maf table, there are other ways.

Silverhawk_02TA

Well, I started typing up a nice long reply explaining why you were wrong, but then I realized you weren't!

Got my polarities crossed! My trims were indeed negative, and not positive, seeing as I was running so rich due to the less dense air. Thanks for keeping an eye out, Another_User!

Silverhawk_02TA

That's a good point. Something I've never thought of. I would imagine that it would open the door to all sorts of fueling problems without the VE table to pick up the slack of the MAF during throttle transitions. It would be interesting to see what would happen. Maybe someone who still has their MAF will volunteer?

God Forgives I Dont

Tell me How to do it! I still have my Stock MAF with screen connected I just have the fail set to 0 at the moment.

Like you said there may be a lot of problems in the transitions but maybe if I drive just right I can isolate the MAF HZ and adjust to that. Difficult yes, but just might be posible.

God Forgives I Dont

P Mack - I just haven't had good results with any of the Airmass calculators and I've tried a couple of times and there not all that close of results.

Silverhawk_02TA

Engine>Airflow>Dynamic Airflow

Look for a field called High RPM Disable. It's on the left near the top, and has a value of 4000. Whatever you change it to, above that RPM, only the MAF will be used, with no interference from the VE table, aside from error checking.

Good Luck!

Another_User

Actually, I don't think that is accurate. I have read a lot of stuff about this, and (including HPTuners help file) the MAF measured airflow above the "disable" is still filtered. It sounds to me like there are still corrections being performed on all MAF calculated airflow, even thought the airflow is entirely MAF based beyond the disable threshold. If that makes any sense? I wish gameover would respond to my post and give us some more info on dynamic airflow calculations...

leaftye

That's kind of what it did for me. I just moved from Albuquerque, NM to San Diego. In New Mexico my LTFT's were around -2. In San Diego they shot up well over +10...engine was knocking all over the place, and the LTFT table was dark red in HPTuners...ack! So far I've added +18 to every cell in my VE table, and getting close to being able to nail down each cell...hopefully I'll be there in a couple of days.

Another_User

Good luck...that VE table can be a PITA.