The table of MAF frequency vs airflow has a set number of breakpoints. The value of the reported airflow can be changed but the frequency of the MAF cannot be changed easily.

People "scale" the maf by scaling the upper airflow values. This allows the pcm to calc for higher airflow, and report the higher airflow numbers (allowing more fuel compensation) so the PE vs RPM table doesn't have to be jacked quite as far

Here's what several of the tables look like:

http://www.carprogrammer.com/Z28/PCM...comparison.htm

To be honest you can just change the peak value in the MAF table, since the pcm will use that once the MAF maxes the table. some people like to change the slope of the whole thing, but unless you've got a ported MAF it's not needed. The trick to tuning is to get the best results with the least number of changes in my opinion.

Hope this helps,
-Christian

www.carprogrammer.com

 

I couldn't agree with you more!!!!!

 

so you can just change the 471gps reading at the 11216 freq up to 510gps, and thats it? Is this the highest that the PCM will utilize then?

Bill

 

well 510 would be the max at the same point anyways.. so there is really no difference.. The idea with this is to extend the PCM's range.. lets say you put 510 on the max value and you will still get a maxed maf anyways... it will not prevent the maxing on the maf.. there is a limit on the frequency the PCM can process... So... you will get 510 at exactly the same air flow instead of 471... as a matter of fact you can make the pcm "see" any airflow.. but you will still have a maxed maf at the same RPM... so it would be to tune either on SD or to tune with the PE vs RPM up top a lot...

 

I understand the frequency limit, but doesn't the PCM use the airflow number in fuel calculations. I understand that you cannot prevent the MAF from maxing out, but if you modify the 471gps to 510 (can it be more?) the PCM will use this number to supply more fuel at that level when the MAF is maxed, thus requiring a smaller change in the PE numbers to keep the AF ratio constant?

I guess what i'm trying to say is the 11216 Hz is a physical limit, correct? The computer cannot recognize a freq higher than this level. Can I still change what flowrate this value corresponds to to anything i want or is 510gps a physical limit also, whereas any number higher than this will not correspond to an increase in fuel by the pcm. ie. when the MAF is at 11216 Hz i could not change the table to say 520?

Hope that what i'm asking is clear

 

No.. tunercat will not let you use a higher value than 512

 

The max value should be 511. The possible values are 0-511 since it is a 9 bit integer value I think. Not really sure why they use a 9 bit integer...must make the table smaller in memory, but must be a PITA to actually read a specific value out of the table

 

Both are limits in the PCM. The MAF will report higher frequencies (not a lot higher though.) The PCM table would have to extended to interpret higher frequencies. This has not been done.

The PCM sums two eight bit accumulators X and Y each with a max value of 255, which yields the 510 max value. This is a computational limit for the pcm.

Since both limits are inside the pcm, a valid hack would be to change what's going into the box. For example use a frequency divider to halve the MAF frequency, thus underrepporting the input. Also halve the injector sizing, thus underrepporting the output.

Can't remember if this has been tried, would be a great thing for LJ to try out (electrical knowledge plus 9 sec blown car)

Hope this helps,
-Christian

 

I know this is completely off the subject, but does the TPI PCM have a X and Y bit accumulators that it adds together? I have never looked at one or the other so that is why I ask.

Thanks
Jeremy

 

Hi Jeremy, Haven't played with the TPI ECM much, what model/ code you looking at ? The GMECM list would be able to answer this for you. You can see the info for them here:

http://lists.diy-efi.org/gmecm/

Hope this helps,
-Christian

 

Highlander,

I am no expert....But I thought I would just ask,

Do you have a ported MAF?

I spoke to both Shalin Patel and Bryan PCM for less tuning in the past and they both told me to trick the maf so it maxes out at a Slightly higher RPM, its best to port out the maf. They both said if a car running boost and a Stock MAF, maxes out at 5000Rpms, a well ported maf will reach its 471 Max Limit around ~5300 rpms, thus allowing a little more RPMs for tuning.

You probably already know this but I thought I would just throw it in to see if you have tried it already and had any sucess with it.


Thanks,
Claude
Only Tryin to Help and Learn at the same time

 

The ECM part # is 1227165. It was used on the 86-89 TPI cars with MAF. I was wondering bcuz the guys on thirdgen said that the MAF had a limit of 255 and was wondering if they got that # by just the x or y and not by combining them together.

 

I do have a ported maf and comparing it to my stock one is highly ported... That was one of the reasons I used the ported one and not the stock one, actually I was thinking about porting it more and adjusting the tables to where i needed to... But honestly I didn't know if it worked or not... and now I confirmed it