MAF Question

[mark99hawk]

I did my first two logging sessions with HPTuners today.

1. I unplugged my MAF (and turned off the SES light for the codes it would set) and did some logging. The LTFTs were all between 0 and 2 with most of them sitting at 2. Seems not too bad for the stock tune.

2. I then plugged the MAF back in (and flashed back the completely stock program) and did some logging. The LTFT's are all sitting around 17. The lowest they go is 9 and the highest is 20 (most are 17).

Both times I drove for at least 30 minutes at varying speeds and loads. I did reset the LTFTs before the logging.

Am I really running that lean with the MAF plugged in ??? ? This is a basically stock '99 Trans AM (LS1) - just an SLP lid and catback as modifications so I find it hard to believe it is that far out... ???

Thanks!

Mark

[mark99hawk]

Forgot to mention that I soaked the MAF in electrical parts cleaner just to make sure it didn't have any contamination on it.

It is the stock MAF with the screen intact.

Mark

[chrisj6]

You need to do some driving around before you log to give the PCM some learn time, you are not getting accurate numbers directly after the flash. Give it some learn time then go back and log.

Chris

[mark99hawk]

You need to do some driving around before you log to give the PCM some learn time, you are not getting accurate numbers directly after the flash. Give it some learn time then go back and log.

Chris

I drove around for about 30 minutes before I started logging - is that not long enough?

I did do a log before I started all this (about 2000 miles since the PCM was reset) and I got the same thing. This was before I touched the MAF or anything...unfortunately I lost the log since I didn't know how to use the scanner but I do know the numbers were all around 17...

Thanks,

Mark

[12secSS]

Mark, you did everything correct. And yes, I have noticed some MAF run lean when plugged in. My truck for example did the same thing. I recalibrated my MAF table using RedHardSupra's excel sheet and all is great now. 8)

http://www.allmod.net/hpt/

[mark99hawk]

Mark, you did everything correct. And yes, I have noticed some MAF run lean when plugged in. My truck for example did the same thing. I recalibrated my MAF table using RedHardSupra's excel sheet and all is great now. 8)

http://www.allmod.net/hpt/

Strange. I would have expected the factory setup to be much closer to correct than it appears to be especially since I have virtually no modifications done to the car.

Oh well - off tuning I go I guess Just wanted to make sure the MAF was working right before I tried to tune anything.

Mark

[98_LS1]

Probable GMS MAF solution???

I tuned with the MAF unplugged and updated the Secondary and the Primary VE Tables. I had the LTFTs at 0 to -4. When I plugged the MAF in, My LTFTs went to +14 to +20. I just Multiplied my MAF Table by 1.30 for the GMS MAF sensor. All my LTFTs went to 0 to -4.

[12secSS]

Yup, I have seen very conclusive effidence that the GMAS runs a car very lean. If you choose to run a GMAS, you should calibrate it using RedHardSupra's calibration file. It has worked flawlessly on my 2001 Camaro SS and my 1999 GMC Sierra. Do not scale the entire MAF Table by a single value, it is not a linear graph.

[mark99hawk]

Probable GMS MAF solution???

I tuned with the MAF unplugged and updated the Secondary and the Primary VE Tables. I had the LTFTs at 0 to -4. When I plugged the MAF in, My LTFTs went to +14 to +20. I just Multiplied my MAF Table by 1.30 for the GMS MAF sensor. All my LTFTs went to 0 to -4.

I still have the stock MAF Odd that it is behaving like an aftermarket one...

Mark

[12secSS]

Is your's ported or descreened? If not, this further backs up the arguement that GM did not spend time calibrating the MAF sensor, just set the table up to be satisfactory to initial production needs. You should consider calibrating your MAF sensor using RedHardSupra's spreadsheet, it worked for me.

[mark99hawk]

Is your's ported or descreened? If not, this further backs up the arguement that GM did not spend time calibrating the MAF sensor, just set the table up to be satisfactory to initial production needs. You should consider calibrating your MAF sensor using RedHardSupra's spreadsheet, it worked for me.

Nope, not ported or descreened.

Once I get the VE table tuned right I will try out that spreadsheet and see how that works

Amazing how much better the car runs with the MAF unplugged right now...(+4 LTFT's instead of +17).

Mark

[redhardsupra]

if the car 'wakes up' without maf that means maf is severly miscalibrated. i had the same thing happen. now that the maf is calibrated, there's no difference in drivability between maf and sd modes.

[livinthedream]

if the car 'wakes up' without maf that means maf is severly miscalibrated. i had the same thing happen. now that the maf is calibrated, there's no difference in drivability between maf and sd modes.

Turns out my stock MAF with the 98 C5 has an almost identical curve to the Monaro. After tuning STFT's are basically the same in SD or non-SD mode. Sweet!

[NightRiderWS6]

My car is up for tuning next.. however there's a difference.. I've got longtube headers and a 3" TSP Catted Y Pipe on my 1998 WS6.. totally stock MAF as well.. After a scan session with HPTuners today my car is doing the same thing with a nice all red graph of LTFT's everywhere from +11's to +20's.. not much other then those ranges.

Could this be because of the headers though?

Marky.. we're gonna spend some time this week driving around! Your car works great now!

[jimmyblue]

You can get big positive trims from closed loop
false trimming, sleepy O2s look like lean O2s to
the PCM. Look at the switching waveforms and
see if they're fast and even, or mostly low with
the occasional groggy jump-up.

[98A4LS1]

My '98 also runs lean with factory untouched MAF. +9's
The only mods are air lid and ported TB. I'm trying to decide whether I need to adjust the MAF Cal table or VE table.

[mark99hawk]

I did manage to get the LTFT's to close to 0 most of the time by first doing the VE tuning thing and then turning the MAF back on.

My MAF calibration using redhardsupra's spreadsheet looks very odd but it does work so I'll leave it the way it is. (my calibration is much much higher than even the aftermarket MAF's on the spreadsheet)

Mark

[chrisj6]

Tune VE first, then go in and calibrate the MAF. In tuning the VE first you will know how uncalibrated the MAF is.

[Dellz06]

Hey 98_LS1,

After you adjusted your MAF table by a percentage, does your exhaust pop more on deceleration? This is something I've noticed with my tune with my LTFT's about the same (between -3 and +1).

I also get a little more idle hunting for 800 rpm if I coast down from 60 in neutral. Once I'm stopped, it doesn't hunt anymore.

EDIT: It also seems to be somewhat temp dependent. On a cold day, the exhaust sounds absolutely killer with a nice mean Borla growl, but on a hot day, it pops and crackles, almost to the point of a backfire.

John.

[98_LS1]

Yeah, actually, it does pop more. Kinda strange how it happened to 2 people. When it is cold outside, the exhaust does sound helluva lot better. I got Magnaflow though. I unplugged the MAF again, and started getting my trims back to 0. I'm pretty close. Once I get them all to 0 +/-1 I'm going to recalibrate the MAF using redhardsupra's spreadsheet. Seems to be the best way.