MAF sensor / hard shift question.

[Pinger]

I found that my MAF sensor was without its fused 12V supply and when I put that right the hard up-shifts ceased to be a problem.
What if, the MAF sensor didn't see air flow but was connected electrically. Would the PCM behave as though the MAF sensor was electrically disconnected and resort to hard up-shifts?

This would only be for up to half throttle opening (at most) as larger throttle openings would see air flowing through the MAF sensor - but not all that the engine is consuming. This is for a modification I'm thinking about for my LPG (propane) system.

 

[Schurkey]

I expect the hard upshifts are due to the computer running the engine and trans in some sort of "Limp Home" mode; because the information presented by sensor(s) is unreliable. It's better for the trans to shift too hard than to slip.


Screwing with the MAF sounds like a recipe for disaster; you'd be deliberately falsifying data the computer expects to have in order to provide proper fueling and spark advance. But I've been wrong before, and I don't know LPG conversions at all.

 

[Supercharged111]

In the event of a perceived MAF failure, the PCM will revert to FULL line pressure. This can be catastrophic to your trans case. I was running my black box PCM in open loop mode which meant the PCM saw the MAF as failed. The shifts were brutal, I just figured that was the nature of the shift kit. Knowing what I know now, I don't think that that was the case. I believe the black box maxxed out my line pressures and was the reason for me breaking the case on my 4L60E. It broke at the servo, about half of the retaining ring diameter broke off the case and kinda wedged the servo in there and limited its travel. I was left with a 4L60E that had 1st-3rd, but with some weird ass shifts. I did a 4L80E swap with a shift kit and the shifts were still pretty manly, but again I figured this was normal. For whatever reason, I plugged the MAF back in one day and all of a sudden part throttle shifts were humane while the WOT ones would still slingshot you good but not brutally. I later swapped to the 411 PCM which has a few parameters you can change to enable a MAF failure without the trans reverting to full line pressures. The black box did not posess this luxury so I never knew it was a thing up to that point. Since then, I've decided I like the MAF a lot, but it presents some new challenges in the supercharged dually having datalogged a bit at lower elevations. Case in point: I can scrape by at 6000' with stock tables, but anything south of that demands a bit more attention to the tune and either some deletion or modification of the norm.

 

[Pinger]

In the event of a perceived MAF failure, the PCM will revert to FULL line pressure.

Yep, that's where I was when its fuse was missing....

I plugged the MAF back in one day and all of a sudden part throttle shifts were humane while the WOT ones would still slingshot you good but not brutally.

.....and when reconnected - as above.

But will the PCM perceive a lack of air flow as MAF failure or does it only recognise electrical malfunctions?

 

[Pinger]

I expect the hard upshifts are due to the computer running the engine and trans in some sort of "Limp Home" mode; because the information presented by sensor(s) is unreliable. It's better for the trans to shift too hard than to slip.

Deduced at the time that it was defaulting to full line pressure - and definitely wont be going back to that.

Screwing with the MAF sounds like a recipe for disaster; you'd be deliberately falsifying data the computer expects to have in order to provide proper fueling and spark advance. But I've been wrong before, and I don't know LPG conversions at all.

Spark advance is relevant here, fuelling not as LPG fueling is independent of MAF. That said, I don't want to lose the ability to run on gasoline but it ran OK (AFAIK) on gasoline with the MAF missing its fuse - the hard up-shifts were the problem.

 

[Supercharged111]

Yep, that's where I was when its fuse was missing....

.....and when reconnected - as above.

But will the PCM perceive a lack of air flow as MAF failure or does it only recognise electrical malfunctions?

If it underreports airflow, your line pressures will be too low among other things.