Car stumbles terribly with MAF unplugged

[Dirk_Diggler]

Fooled around with the sec ve table and seen the ltrims move the most they have since i started all this. I think i went to lean on this table and it moved the ltrims +18 so i scaled it back and got it in line. I am still wondering about the stumble now since i cant tell the difference between the stumble and the car comming onto the cam ~2k rpm but anything below that just feel soggy comapred (being the key word) to 2k+

[Chris@HPTuners]

remember messing with the VE table affects where you are on the Spark table as well.

[Dirk_Diggler]

Question that has plagued me for the night......


Seeing there is a primary and secondary table one would asume the primary table is used when the maf is unplugged as a base for all calculations and fueling. Why would GM ignore the primary table and use teh secondary table for fueling. The sec tables is less precise than the primary table and seems more lie a gross calculation that anything.


Oh and the timing issue could i just go to the 400-80-1200 colum and add 2-3*.

Thanks for all your input Keith, Chris and others.

[Chris@HPTuners]

in early code such as yours (9381344) the airflow calculation has two VE tables. The primary table is used whilst the MAF is connected to sanity check the MAF (ie. for the P0101 check). If any MAF DTCs are set P102/103 then the secondary table is used for airmass calcs used for things such as the fueling and spark derived airmass values and the primary table is ignored.

In later code the primary table does both.

[Dirk_Diggler]

Darn 2000 MY Are there any updates to the Os thats available to use where i get that capabilty and the resolution of the primary table? Or is it moot at this point?

[Chris@HPTuners]

if you have VCM Suite Pro you can change that (in fact Keith did exactly that on his car that was running the same code as you).

[Dirk_Diggler]

Looks like I am SOL then

[Bink]

remember messing with the VE table affects where you are on the Spark table as well.

Chris - Does this^^^ apply only to MAFLESS??

I guess the PCM uses the AIRMASS Calcs for the Timing g/cyl when on the MAF?? TIA.
joel

[Chris@HPTuners]

yeah it's for both MAF and MAFLess, but when MAFless it is a direct correlation.

[Bink]

yeah it's for both MAF and MAFLess, but when MAFless it is a direct correlation.

Thank you.
joel

[Nic]

in early code such as yours (9381344) the airflow calculation has two VE tables. The primary table is used whilst the MAF is connected to sanity check the MAF (ie. for the P0101 check). If any MAF DTCs are set P102/103 then the secondary table is used for airmass calcs used for things such as the fueling and spark derived airmass values and the primary table is ignored.

In later code the primary table does both.

Is it safe to assume that all 99 PCMs function in the same way as the early code 2000 PCMs?

[Chris@HPTuners]

if your VCM Editor shows a secondary VE table then it does. In later code the secondary VE table doesn't exist and hence does not appear on the editor.