Question about relation of MAF signal to trans

[Trannyman95]

I dont feel this is a good question aiming directly as a question for HPTuners since it is not a known tunable table, but I do have a question that hopefully a tuning guru or pcm hex expert can shed some light on. I mainly tune GM 3800 equipped cars stock to wildly modded and have read about and personnally experienced that if the maf signal is too low than the auto trans line pressure is also low and causes the trans to slip and even mis the shift and hit the rev limiter. I know this is not a table on HPT or any other tuner to my knowledge, but does anyone what know how exactly one is related to the other?? Is there a certain point of maf reading that from XXX and higher airflow it is just max commanded line pressure or is it a scaled line that gradually gives more line pressure with more airflow? For example, and my first experience on my own car, I made some changes to my intake setup and my car was running very lean and my trans was slipping so bad at WOT that I was hitting the rev limiter 400 rpm higher than my commanded shifts. Well some engine carnage followed and after investigating the problem I found my MAF readings very low because of the intake changes I had made. After retuning the car and altering my maf readings the trans shifted firm and right on the money like it always previously had. It seems like any lower than 30 lb/hr on the maf scale and the trans pressure is nowhere near where it should be and the trans slips at WOT. Rescaling things and getting the maf numbers up to around the 40 lb/hr range seems to make a very substantial difference. Again these are 3800 cars f-body and w-body and I dont know that this applies to the V8 cars but I would imagine it does. Does anyone have a good answer or has broken down some code in the pcm to actually find or look at a table such as this if one exists? With absolutely no other change to the car, or any other car for that matter, the maf readings directly effect line pressure and I would really be interested in the hows and whys if anyone can help. Thanks for all those who took the time to read this and can share some knowledge to clear up this gray area I stumbled upon.

Dave

[IndeedSS]

Not sure if this will help:
The Throttle Angle Calibrator (TAC) was specifically designed to alleviate the problems faced when significantly increasing the throttle body size on any OBD-II controlled engine over that of the original throttle body size. The reason for problems resides in the way the Powertrain Control Module (PCM) determines operational conditions of the engine and transmission based on throttle position. The PCM relies on the TPS signal to predict a minimum of three powertrain parameters.



One parameter is the amount of torque levels delivered to the transmission. With an oversized throttle body in place, the engine will produce significantly more power and torque at the same throttle angle due to the additional air allowed by the larger throttle body. This can cause serious problems at lower throttle settings where the PCM is not properly anticipating the higher torque produced by the engine. When the engine is producing more torque than expected, the PCM is not commanding sufficient transmission line pressures to the engagement clutches. If the clutch pressure is insufficient, then the clutches can slip, get scorched and eventually fail prematurely. The TAC will signal the PCM to the higher torque level at lower throttle angles and the PCM will respond by increasing transmission line pressures. This will result in maintaining sufficient clutch engagement and prevent clutch slippage.

Another parameter is the PCM should be crossing over from closed loop operation to open loop operation when higher air flow rates are achieved. When a significantly oversized throttle body is used in place of the original throttle body, then excessive air flow is allowed into the engine while the PCM remains in closed loop operation. The TAC signals the PCM that the effective throttle angle is greater to match the higher air flow. The PCM will then respond by switching over to open loop operation. This can save the engine from higher throttle fuel mixture control instabilities not supported by closed loop operation. In some conditions, the TAC can prevent engine damage.

A third parameter is the point at which power enrichment is triggered. The TAC signals a higher effective throttle angle than the actual position. This allows the engine to richen the fuel mixture at an air flow rate more appropriate for the larger throttle body. This also allows for more power at these throttle positions as well as holding off the onset of avoidable knock retard.

The TAC differs significantly than throttle position sensor enhancers that are currently available in the automotive aftermarket. These TPS enhancers do not affect the TPS signal at low throttle positions. They only make any changes at typically ~70% throttle and then discontinuously switch the signal to 100%. The TAC operates dramatically different. The TAC starts by giving the PCM the same idle position signal as with the original throttle body. However, immediately off idle, the TAC begins to send the PCM an increasingly higher effective throttle position relative to the original throttle body. This higher effective signal continues to increase until approximately half throttle is reached. At that point, the effective offset is gradually reduced until full throttle is reach where the TAC output is 100% just as the original throttle body. This approach means the TPS signal sent to the PCM is smooth and continuous without any drastic jumps. This results in the PCM producing smooth transitions in the control of the powertrain.

I know the few people I've contacted about this has said the TAC has cleared up shifting problems after goiing with a Northstar TB. This concerns me some as well.

[TooMch]

Wow! that's a lot of research.

[Trannyman95]

Thanks for the info on the TAC Lee! My concern isnt driving around though, I am comparing WOT to WOT where the TPS signal is maxed, pegging the peddle to the floor on a green light.....Yeah the rwd cars can get away with that lol. I have never ran into any issues with TPS being a concern in the past with trans shifting behavior. I just know at full throttle when the maf signal is too low so is line pressure and am just looking for that relation. The bigger problem that I am finding is Calculated Torque, which I am assuming is another calibration inside the pcm directly related to maf flow. When you switch to a larger maf sensor that reads lower at WOT then the calculated torque numbers are also lower and if you look at transmission tables they refer to torque but how it uses this number could be up in the air. On HPT scanner I was able to use calculated transmission torque and it only went up to 275ish, which is way off for my car as we both know! There is a PID for engine torque but it is not supported by my 97 F-body 3800 pcm so I cant view it. I believe maf airflow is in the calculation to determine torque and by having lower maf readings the pcm essentially sees less torque and drops to lower pressure numbers and higher shift timing in the transmission tables.