I'm putting this here instead of the computer/tuning section because it applies to boosted cars. What is the fix for setting the MAF high code under boost on 96/97 LT1s? This is the second car I've seen this on, never resolved the first. Apparently maxing out the MAF at 5xxx rpms and the car going lean and setting the MAF high code. Is it as simple as setting the value for MAF High Fail higher in the cal? I can see this maybe keeping the code from setting, but what about the car going lean? I'm using TC OBD2.

 

The MAF output is exceeding the limits of what the PCM can interpret, which you cannot change, but I believe you can disable the diagnostic code if you're only trying to get rid of the light. Check the Fuel and Air Diagnostics menu under Switches. I haven't done this so I don't know, but possible the MAF Sensor Circ High Frequency switch would do the trick?

One way to keep adding fuel afterwards would be to adjust the %Change to Fuel/Air Ratio at WOT table.

 

Yes, this has happen to me (97SS 383 - D1). It goes lean when MAF threshold frequency is exceeded (usually @ WOT and PE mode enabled). I have LT1edit. I saw they had a new feature in version 2.2 (Set MAF high to the max (60k+ from 10.7k). So, I paid an extra $100 for the upgrade. Now it does not lean out as in the past. From past information (ala... C. Millard) speculated that OBD2 cars (96 and 97) cut the injector pulse width in half when in WOT mode and MAF freq. Thresh-exceeded. My experience has validated this for me, and, I am glad to say, I have it under controll now. I do not lean @ WOT. Also, other features in ver 2.2 allowed me to alter low speed closed loop afr. This was also a problem for me. The other alternative is, bigstuff3 or FAST speed density @ $3k+.

 

I had heard there was a fix with LT1Edit, but I'm using TC OBD2. I'm going to try upping the MAF fail freq to 15000 and turning off the P0103 code. I'll let everyone know if that helps. I have to ship the PCM back to the guy I'm trying to help on this so it may be a couple of days before I find out if it helps. Here are some replies I got when I had this problem on the first car that never got resolved.
http://web.camaross.com/forums/showt...ighlight=P0103

 

Where are you changing the MAF fail frequency?

 

With TC OBD2 it under Constants>Diagnostic Parameters at the bottom of the list. Setting at at 15000 may not be enough and someone said in the other thread that it had to be set lower than the highest value in the MAF Cal Table. I know on LS1s it doesn't have to. But I think turning off the P0103 code may make the valve in the High Fail parameter a moot point. Even if it exceeds it, it won't set the code.

I know on LS1 cars, any MAF failure (code) will default the car into speed density mode. I'm thinking setting the P0103 code may be doing the same thing here and just having the PCM ignore the P0103 might keep it fueling off the % Change at WOT Table. I think LS1 cars will continue to fuel off the PE even after they max the MAF. I never got a chance to try that on the first car I had this problem on.

 

Cool, I never saw that there before... I wonder what frequency the MAF is actually capable of outputting. The MAF calibration table only goes up to 11216Hz.

 

If I ever get this car on the dyno, I'm going to log that parameter if I can. On the first car I had this problem on, I only logged MAF SAE lb/min. Didn't think to try and log Freq. I use my HP Tuners scanner on the 96/97 LT1s and it only lets me log SAE PIDs, not the GM Enhanced PIDs. I have Autotap also and maybe it will let me log it.

 

Cool, post when you do. It appears that the PCM will only know how to interpret up to 11216Hz though, unless there is an extended MAF calibration table hidden somewhere and not displayed in TC. I would guess that you're still going to be in trouble, and have to resort to using the %Change to Fuel/Air Ratio table.
Another idea is to get rid of the MAF altogether and try tuning in SD mode w/ a 2-bar MAP sensor. That way the fueling while in boost would be sensitive to MAP, not just RPM. I don't think anyone here has ever done it, but it's been talked about. I'd like to see someone try it...

 

MAF high failure threshhold max... 65535. Higher values will not be accepted.

 

65535 what?

 

HZ. I think he's saying that is the largest number the program will allow you to enter in that field.

 

Is that ceiling high enough so that the MAF will not max out? Where would one expect a 15lb boost car to be?

 

If you disable the the P103 code it should fix your lean problem. I think when that code is set it reverts to open loop or speed density can't remember. So if you don't set the code it will work like its supposed to.

 

Ok, that's the highest number you can set the failure high freq limit to. But the MAF calibration table is still limited to 11216Hz; how will the PCM know what mass of air correlates with any frequency greater than that? It won't fix the lean condition, just keep the SES light from turning on.