Thread: Hesitating shifts

Originally Posted by Trannyman95

An LS1 maf or the SLP and or GM 85mm maf will be plenty. I have a GN that i work on a bit that has an LS1 maf and even pushing 26 psi with a TE60 turbo it left plenty of room. You can rescale all you want with the maf with the tuner. You are correct that the HZ is going to be fixed going in, but it wont matter. The stock pcm only reads to 11500 whether the sensor puts that out or not. If you install an AFC and lower the max value of the maf output then it may only read to 10,000 but that is still max and wont read any higher so what are you gaining by doing that? Then you wont even use the high end of the maf table in the pcm because it will never send the signal to read that high. And as mentioned earlier why is it a big deal if the you are running out of room? There is more to fueling than just the maf table and that is where your tuner comes into play. Pluggin in the afc is only going to move your problem to a lower output frequency, and as mentioned earlier your fuel trims will all be off and you will have to redo the maf table in the pcm anyways. Also keep in mind that lower maf #s mean less trans pressure at part throttle and even full throttle if you start scaling back too far. The pcm doesnt really look at the HZ, it looks at the airflow numbers that you see in your tuner and that is what everything is based on, so again the AFC isnt doing anything you cant do with the tuner other than making the number going into the pcm less than it should be. ZZP doesnt even sell the AFC anymore, so if they were such a requirement then they would still be available but because tuners are readily available they were fazed out.

I am not trying to sound like an ass here but I just don't think were are on the same page. If I scale the maf with an AFC the pcm will still beable to read 11500hz.

Originally Posted by TDCRacing

So what happens when you do max out the maf?

The pcm uses the 11500hz grams/sec cell for fueling causing the car to go very lean.

On a side note the sensor will read above and beyond 11500hz because when I out flow it I have seen 11550 on the pt. The table is the limiting factor.

I know what you are saying, yes the pcm table stops at 11500 but that doesnt mean you need an AFC to tune the car, again they dont even sell them anymore because it is not needed to tune the car and you dont need the maf table only to rely on WOT fueling. How high does the sensor actually read??? Good question, but as I mentioned a few times before keep in mind that you have to rescale your entire MAF table to compensate for this if you make the input value lower with the AFC. ALL of your fuel trims will be wrong except in PE mode where it doesnt use them, but once you lower your maf input then the car will run excesively lean since you will have to lower the signal a bit, and then you have to go into other tables to add fuel anyways so why waste time with an AFC? You have a tuner and again the maf table is not the only thing to use for WOT fueling. Buick GNs max out the maf often when only at half throttle or not anywhere near peak boost and rpms but is not a problem because proper tuning corrects this. Once the maf input is at the max of what the pcm can read then the maf value will continue to climb but the pcm only uses the last highest point on the table. If you want to use the AFC to help your problem that is fine and you will have a lot of work making fuel trims and WOT fueling correct again, I am just trying to make you realize that it is not necessary and that the vendors dont use them anymore because it can all be done in the tuner.

Originally Posted by Trannyman95

I know what you are saying, yes the pcm table stops at 11500 but that doesnt mean you need an AFC to tune the car, again they dont even sell them anymore because it is not needed to tune the car and you dont need the maf table only to rely on WOT fueling. How high does the sensor actually read??? Good question, but as I mentioned a few times before keep in mind that you have to rescale your entire MAF table to compensate for this if you make the input value lower with the AFC. ALL of your fuel trims will be wrong except in PE mode where it doesnt use them, but once you lower your maf input then the car will run excesively lean since you will have to lower the signal a bit, and then you have to go into other tables to add fuel anyways so why waste time with an AFC? You have a tuner and again the maf table is not the only thing to use for WOT fueling. Buick GNs max out the maf often when only at half throttle or not anywhere near peak boost and rpms but is not a problem because proper tuning corrects this. Once the maf input is at the max of what the pcm can read then the maf value will continue to climb but the pcm only uses the last highest point on the table. If you want to use the AFC to help your problem that is fine and you will have a lot of work making fuel trims and WOT fueling correct again, I am just trying to make you realize that it is not necessary and that the vendors dont use them anymore because it can all be done in the tuner.

Ok I get what you are saying. How do you properly tune the car then? The fueling will be based off of the 11500 cell right? I guess that part I don't get. Also why can't I just scale the maf when I am in pe, why would I have to scale the whole table? Not saying you are wrong, I am just not seeing it I guess. I was playing with the afc lastnight and scaled from 10000 to 13000 on the afc and it seemed to be working right. I was just having other issues which are in another thread. I guess if you can explain how to tune and not use the afc I would more than happy to not have to use an afc.

To clear up what I meant about being in PE mode, the LTFT and STFT - the pcm will NOT make any fuel trim adjustments in PE mode, which is dependant on what you have your table set to and usually is in the 30-45% range depending on rpm. Once it goes into PE mode then it is essentially open loop which means the pcm does not use the 02 sensor for fueling and works off of fixed tables. Lowering your maf signal with an AFC will cause ALL of your maf numbers to drop unless you have a V2.x AFC which I believe allowed you to tweak different areas which would be benificial but still require lots of maf table and fueling tuning. Lowering your maf input helps your maxing out at 11500 problem BUT also means that the entire maf table will read too low and the car will run lean, so you will have to add fueling back in. For part throttle driving the fuel trims will change, going positive because it needs to add fuel because the car is running lean. You will need to roughly add the % off that the fuel trims are back into the lower end of the maf table to correct the trims being wrong. You can do this up to your PE enable point is so part throttle driving has the correct fuel trims which is important as WOT will referrence to this and they need to be as close to zero as possible. Since your entire maf table is lower due to the AFC being line your WOT and anything in PE mode fueling will be too lean. Generally, and most accurately, you adjust this with the maf table so you will have to correct this also. Without a wideband you are only going to be guessing where you are at but you can get in the ballpart without one. One problem you may run into and as I mentioned earlier is that by dropping your maf signal you are also going to cause the trans to have lower line pressure and cause softer shifts and delayed WOT shifting. You run into this when scaling back the maf too far or by running a much larger maf sensor/ported large throttle body/large intake pipe but every car is different. If you are using a PT this is where you are going to get into trouble as I dont believe you can adjust the pressure control solenoids amperage tables which is needed when maf numbers are low as you need to decrease the amperage in certain sections of the table to bring your trans pressure back up.