MAF is part of the equation the pcm uses to determine line pressure in an A4. When the pcm switches to Speed Density mode reacting to a "bad" MAF, it will also raise line pressure significantly. What has been done to get around this?

 

I believe that that problem was fixed in 99..and it is only still a problem in 98's...but can be fixed..sorry no details..I just know there are people that can fix that problem on the 98's

 

if you have HPT send you file to gameover and he will change some stuff for you to run mafless where the a4 is controlled by the maf if you are running EFILive you can turn em off by yourself

 

There are several DTCs that can cause the PCM to command maximum line pressure in an Automatic in all year models, including some that are related to the MAF.

Raising the values in the MAF table by more than 10 to 15% can cause higher line pressure, or so that has been the thought for many years. Has anyone proved that wrong? And if that is the case, what happens when there is no MAF signal at all?

 

What exactly is done in any of the programs, I have them all.....well...HPT, EFILive and LS1edit. lol If it is just a matter of turning off the codes that command high line pressure, I can do that. But I believe there is more to it than that as sometimes there is no code set when the pcm calculates a wrong engine load because of the MAF and line pressure is not right.

 

I think it is only the codes that makes it command full line pressure. If you set the 102 code to not allow full line pressure then you are fine.
Adaptive shift learning could change things, but That is for a different issue.

 

That statement is false. On 2001-2002 vehicles if you zero out the MAF Table, the shift pressure is not increase to full. I know this from my vehicles experience and non have done this. Only 1998-1999 vehicles, mainly trucks.

 

That dosen't have anything to do with what I said. I did not 0 out the MAF Table. If anything putting all 0s in the MAF TABLE would reduce the line pressure.

This is just one example for code P0756 for 2001 :

2001 Pontiac Firebird V8-5.7L VIN G Code P0756
Action Taken When the DTC Sets

• The PCM illuminates the Malfunction Indicator Lamp (MIL) .
• The PCM commands 3rd gear only.
• The PCM commands maximum line pressure.
• The PCM inhibits TCC engagement.
• The PCM inhibits fourth gear if the transmission is in hot mode.
• The PCM freezes shift adapts from being updated.
• The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
• The PCM stores DTC P0756 in PCM history.

I do not tune cars to run without their MAFs, just unplug them while getting the VE tables dailed in. My question is, since that has raised the line pressure on 2001 A4s, I am wondering if setting the MAF Senor Fail Frequence to 0 would fix this?

BTW, the above code has nothing to do with the MAF, just used it as an example of how some code will command maximum line pressure.

Thanks, Becky

 

Yes, setting the MAF Fail frequency to 0 (zero) will enable Speed Density without affecting line pressure when tuning. Or at least that is my experience.

I have not experienced any increase (or decrease) in line pressure with my 2001 Camaro SS, neither by zeroing out the MAF, unplugging it, nor setting the Fail Frequency to zero (0). Other vehicles, pre-2000 (as I have not yet tuned an A4 2000), do react to "failed" MAFS.

 

Line pressure was only effected on 98's and very early OS 99's. Its not a matter of turning off a code on hp tuners, its in the operating system. I had my file edited by gameover, now if I set my maf to 0, it shifts exactly the same as it did with the maf on.

 

Efilive allows you to see the transmission dtc fault enablers. There are many times when i see incorrect computer related information in books or on line.

The dtcs that effect line pressure are not turned on in the transmission diagnostics on that car. I can give you snapshots of anything you would like to see, Or, Show you in hex.

 

Using EFILive what parameter changes need to be made to keep the transmission from running high line pressure while running MAFless?


Thanks

John

 

Yes, I know they are turned off, I have EFI and shows that, but max line pressure has still been command on the 2001 Trans Am and also on a 2001 C5. The code I exampled above came on when the tranny was going out in the C5 and it locked it in 3rd gear. But that code was suppose to be off as well. This has even happen on my own car when a code came on that was not suppose to be on from the factory.

The info I posted above is from GM.

 

I have run into this before when I was tunning street cars. I'll see if I can find any of my old notes. This is one of the reasons i would take control of the line pressure away form the computer for A4s... Well, that and to keep other people (tuners) from messing with the line pressure and screwing things up.

 

Thanks Maggie. I would have thought more people would have realized this was happening especially with so many now tuning in speed density. Any info you can find, I would appreciate it.

One option I guess would be to lower the max line pressure temporary until the VE tables and MAF are dialed in.

 

Becky,
I think that temporaly lowering the line pressure is what I did...my long term memory sucks...it's been awhile sence I've tuned anything other than race cars. Most of my tuning files are archived on ezflyer cartridges and i don't have a way to retrieve them easily.

I did find some notes from some of my old work orders but i don't really see anything there that would be of much help. I didn't really find anything that I felt was pertinent but I did find some to be interesting and kinda sorta along the same issues. I will scan them for you anyway.
_____________________________
2001 Pontiac WS.6
Owner ( Delete)
VIN (Delete)

Problem: Transmission line pressure excessive after owner installed 85mm maf



Action: calibrate maf, adjust max line pressure, adjust shift points


Notes:

__________________________________________________ ____________________________

2001 Camaro V8
Owner (Delete)
VIN (Delete)


Problem: Owner says that transmission doesn’t “feel” right and runs “rough” after cam install and mail order tune.



Action: install updated software, tune for cam. adjust for line pressure and shift points



Notes: transmission line pressure was going above 300 with spikes going to 320.
PCM was locked by the previous tuner.


__________________________________________________ ____________________________

2000 Pontiac TA
Owner (Delete)
VIN (Delete)


Problem: Owner says that after he tuned for MAFless operation with LS1 edit he has had to have his transmission rebuilt 2 times. His transmission builder told him he couldn’t run an auto without a maf




Action: repair transmission, install shift kit, vacuum modulate line pressure, reinstall PCM software, tune for speed density. adjust idle.




Notes: maf dtc = enable, maf MIL= NO, PCM calibrations set for Open Loop

 

Its not a big deal, I have noticed no loss in presure running in speed density mode. If something feels different, you can always increase or decrease shift pressure in the affected areas.

 

Must also adjust the MAF rationality table (C2911 in EFILive FlashScan).
If MAF flow differs from MAP calculated flow by more than this table,
then PCM may command max line pressure (and reduces engine output also);
I don't know that there is a DTC for this (which means there is no max line enabler/disabler for this).

 

I have been running my car in SD mode for several weeks. I have not noticed any difference in the way the transmission shifts. Since my car is a '98, my stock .bin file was mofified by HP Tuners to eliminate the harsh shifts while in SD mode. The car does perform better during part throttle and I used a piece of 3.5" exhaust tubing to replace the MAF.

 

Ahhh!...good to know, thanks joecar! Seems like I did know this at one time. I don't get a chance to work much with Flashscan these days and I'm getting old and forgetfull...