Unplug MAF=does not run

[mysunnshine]

I'm trying to do the initial SD tune on a 427ci 05 H2 Hummer and I'm running into a problem. When I disable the MAF in the software and unplug the MAF, it fires up but immediately dies and will not run. My assumption is that there is not enough fuel in the fuel map to support an unplugged MAF. Either adding or taking away fuel does not make a difference. It still will not continue to run even after making those changes. When it's running OL, you can unplug the MAF and it'll continue to run so the fuel map can't be that far off. Any ideas?

[BRD-PREY]

check the map sensor or map wiring, it just happened to me
ed

[mysunnshine]

The MAP sensor works because I have been logging it in closed loop fueling to determine that it needs some fueling changes.

[Taz]

Hello mysunnshine,

I take it your vehicle is using a 5 pin integrated MAF / IAT sensor. Are you completely unplugging the MAF - or just removing the yellow signal wire from the connector ? You need to report IAT to the PCM during the AutoVE process.

What AFR / Lambda / EQ does your WBO indicate when you start the vehicle, then unplug the MAF ? As you know, while using the AutoVE technique there is no type of STFT. Add at least 15% to the VE table before you begin. On unknown parts combinations I have initially added 15%, drove the vehicle about 100 yards, stopped - added another 15%. You may have to make a series of these short trips until you get into a safe "ballpark" for initial fueling.

Also, if your tune uses B4206 (O2 with open loop) or similar parameter - this needs to be set to disable.


Regards,
Taz

[mysunnshine]

The MAF I'm using has a separate IAT sensor. I do understand that there is no LT or STFT when in OL using the AutoVE. I hear ya on the adding 15%. I actually added 10% at a time up to 50% and did the same with taking the fuel away from the fuel map assuming that it may be that far off with the MAF unplugged. Going both ways on the fuel map did not change anything. Is there anything else in the tune that can not allow it to run SD and only MAF. I just hate to get ambushed on this one because it was tuned by somebody else before I got it.

[Taz]

What did your WBO indicate during all of those attempts at fueling changes ?

If the MAF fails mechanically / failed via tune / is disconnected - the PCM defaults to the VE table.

What DTCs are being set ?

I take it this is a DBW a setup - did you also adjust the ETC predicted airflow (to avoid limp mode while tuning) ?


Regards,
Taz

[mysunnshine]

The WBO2 indicated about 20% lean during OL datalogging. As I was adding fuel to the fuel map no changes were indicated by the WBO2 which made me take a closer look at the MAF. That's when I found out that when the MAF is unplugged, it would not run. I actually assumed that if the MAF was disabled in the software that it would not contribute at all to the fueling. It is a DBW set-up and I did not modify the predicted airflow but I have not had the limp mode activated yet.

[joecar]

The PCM fails the MAF (i.e. runs from VE) only if a MAF DTC is present... check for this.


i.e. without a MAF DTC, the MAF table is still being used.

[joecar]

... As I was adding fuel to the fuel map no changes were indicated by the WBO2
...

Which table are you referring to...?

Are you saying that changes to B3605 resulted in no change in wideband lambda...?

Can you sanity test the wideband...?

[joecar]

Does it run in MAF only (set B0120 to disable VE)...? In this mode does wideband agree with B3605...?