Another_User

Now I see why I was having so much trouble tuning my fuel trims. It's not just a good idea to unplug your MAF to tune your fuel trims. You have to. Apparently my MAF and my MAP are pulling the trims in different directions. So whenever I added VE, I should have been pulling it. So how do I tune the MAF with the lid...

WS6snake-eater

So are we supposed to be pulling the MAF when tuning VE? Dude you got me so damn confused now. I haven't pulled my MAF plug at all when tuning LTFT. I think I'm pretty damn close. HPT histogram is showing all white, no green and no red.

HumpinSS

iTrader: (1)

Your trims will still update when the MAF is unplugged so you can continue to use the histogram.

Depending on your year/os number when you unplug the maf the PCM defaults to the secondary ve table. If you see a SEC Ve table in Hptuners you need to use this table with the maf unplugged (keep in mind the sec ve table has less resolution). If you have only a primary table the PCM will go off that for fueling

P Mack

iTrader: (6)

I'm glad you finally decided to try unplugging your maf. Did you run into any problems with it going into limp mode after a while with no maf or anything?

HumpinSS

iTrader: (1)

I have done it for a week or so and didnt run into any problems. Car felt more resposive to throttle changes and such.

Keep in mind. My car, P Mack's car and Another User's car all have secondary ve tables. The PCM will default to this table if the maf is unplugged. The only difference is it doesnt have the resolution the primary ve table has

Another_User

I think it is supposed to use the low-octane spark table when there is a MAF failure. I didn't really notice, my high-octane is copied over the low-octane. I did notice my trims were way off from what I was expecting. As soon as it pulled all the excess fuel from the idle, the car started idling nice and smooth. If you do it, expect your car to run like crap for awhile, and watch out for stalling. Unless your VE table is right already...

Magic Chicken

iTrader: (1)

What y'all are doing is speed density tuning right? What happens after you get it all SD tuned and then you plug your MAF back in?

HumpinSS

iTrader: (1)

Are you making changes to the Primary or Secodnary ve tables

HumpinSS

iTrader: (1)

Who needs the maf anyways after you get it all right. Its a restriction anyways....

P Mack

iTrader: (6)

Theoretically if your maf tables are right your ltrims will stay the same. In reality your maf tables are probably off so your ltrims will change. I think another user was gonna use this process to tune his maf tables once his ve is right.

HumpinSS

iTrader: (1)

Sounds like a good idea. I seen the same thing happen with my trims witht he maf plugged and unplugged`

Chase71Z28

I have a 2002 computer and i was looking at my file on hptuner and i did not see a secondary ve table. So does that mean i don't have one, and when i unplug my maf it will run off the primary. also i have and auto will it affect it. One more thing what years are yalls cars. Thanks for all the help
Chase

Chase71Z28

One more thing i forgot. What codes do i need to clear when i unplug my maf.
Thanks
Chase

nbmls1ta

Sorry for the stupid questions but... I understand the VE is hard numbers for airflow that doesn't change but what happens when you are running off the VE and the humidity changes from day to day, won't that require adjustment to the VE to accomodate? With the MAF doesn't it measure that type of air "quality" change? If I unplug the MAF can I use just the VE to tune idle through WOT? I am very interested in doing this. Do you have to tune a little more "safely" to allow for air density, humidity changes? Is it any less safe to tune without the MAF? I don't have a wideband and usually try to tune using the O2's at WOT and lean/add timing untill there is knock and then back off, can I tune without the MAF in the same way or should I leave a cushion for air density changes? Say I go out and unplug the MAF today and start driving around, can I still rely on the ECM to adjust for stoich at partial throttle or does it run exactly what is in the VE table with no internal adjustments. Can I tune SD using my Ltrims as a guide to rich/lean at partial throttle? Do I need to calculate my VE table or can I just adjust the table to obtain ~0 ltrims for all cells that I hit and then smooth the rest of the table and then the table is correct? When in WOT do I have to use the VE table to richen/lean the mixture or do I still use the PE table? How do you tune the VE table for WOT without a WB? Do I keep tuning the same way I am now and shoot for ~900mv O2's no knock and use the PE table to richen or lean the mixture? When would I have to adjust the VE table for WOT? I am obviously new to this and beginning to become confused. Any help would be GREATLY appreciated.
Thanks alot.
Matt

P Mack

iTrader: (6)

Feel free to correct me if i'm wrong. I'm here to learn too.

No, the ve table stays the same, the fuel trims change to accomodate.

I don't think the MAF can tell the difference between humid or dry air. Ltrims again.

VE should be right for all cases but you shouldn't use it to tweak your air fuel ratio. It is the fuel air multipliers in the pe table that are specific to wide open throttle.

I would just let the ltrims take care of that.

If you instantly go w.o.t. without letting the fuel trims learn, and if your ve is way too low, you could go lean and detonate. If you have forced induction and your manifold pressure goes higher than 105 kpa you could also go lean and detonate. Also I think knock retard is disabled with no MAF which is why it uses the low octane tables.

If it were me, I would not go wide open throttle until i had the maf back on or the ve table dead on.

.

Yes, you can rely on the ecm to adjust for stoich with no maf. Ltrims still update when the maf is unplugged.

Shoot for 0 ltrims, not calculations.

No, the ve table is just used to calculate how much air is going into the engine, you use pe to adjust the mixture.

I would tune the ve table using fuel trims and w.o.t. using a wideband. People have tuned wot with the stock o2's but it's kind of a shot in the dark because the response curve changes so much with temperature.

HumpinSS

iTrader: (1)

You are correct when you say if you unplug your maf it will run off the primary. If i remeber correctly if you have an auto i wouldnt suggest disconnecting the maf as the PCM will apply full line pressure to your tranny and eventually it will kill itself. My car is a 00, another users is a 98 and P Macks car is a 00 if my memory serves me

Another_User

What happens after I tune speed density and plug my MAF back in?
Probably all heck will break loose, because I suspect the MAF is way off because of the lid.

I always change both VE tables. I work on the primary and paste it in the secondary, but I may need to work backwards now since (so I hear, because I have a 09?) the car is only going to use the secondary with the MAF disconnected.

Later cars only use a primary table.

Good call on not unplugging the MAF if you have an auto...I keep forgetting about that.

HumpinSS

iTrader: (1)

I amDirk Diggler on HPTuners forum. If you tune the car to run in SD mode i would prolly leave it disconnected. THe only reason i havent done it yet is because of the lack of resolution with the SEC ve table

Chase71Z28

So if i can't unplug the maf since i have a auto how would i get my ve table correct. If could not program the computer to not give max line pressure.
Thanks
Chase

HumpinSS

iTrader: (1)

WB or you can use the LTrim histogram in HPTuners to get you in the ballpark