Who has maxed out the stock MAF on boost? I was tuning a 96 LT1 Procharger car running 9psi and the car would just hit a brick wall at about 4.7K rpm. looking at the histogram and the dyno chart, does this look like a MAF problem? The car would set a P0103, MAF high freq code when this would happen. We did try a different, but same size MAF with the same results. I always thought it would take much higher power levels to max out a MAF. I've tuned several boosted LS1 cars to 420 ~ 450 hp levels with stock MAFs without this happening. They were at lower boost levels though. I never saw these high of air flows like the histogram shows though.

 

I'm not sure if mine is maxed out or not. Mine reads 44.80lbs/min on a autoxray scanner. This is at 6000rpm WOT at 9psi. So I multiply 44.80lbs/min x 7.56=338.68g/s. My tunercat MAF table goes to 427 g/s. So this would lead me to believe the MAF is not maxed out. I have a descreened MAF so it may not read accurately at higher rpms. I also disabled the High Maf code so it never comes on anyway.

 

That's what I had happen to me also. I had to install the Maf Massager that ATI recommended. This is supposed to "clamp" the signal at a level just below the max threshold for the diagnostic. I later purchased LT1 Edit and removed the high maf from the diagnostics. As was brought up in an earlier thread. I don't know if this was accomplishing the same thing as the Massager or not. Maybe Mark from ATI will see this and give us his input.

 

We had the MAF Massager on the car for a while but it ran so bad with it on that we ended up removing it. That's when we started hittting the wall at 4.7K rpms. I guess we'll try it again. On another board someone posted Carputing was able to do something with their file to extend the MAF range, but I'm using Tunercat.

 

I don't know TunerCat at all. Will it let you disable the high maf diagnostic? I know the tables in LT1 Edit go higher than the point that the diagnostic sets. But the high maf threshold must be well below the max table values.

 

Do you know why that is? The MAF table goes to 11216 hz and the MAF high fail is set at 10700 hz. I haven't tried bumping it up. I can turn off the code, but if you look at the dyno chart I posted, the car just won't rev after the MAF maxes out. I didn't build the car. I'm just trying to tune it. It had a complete motor rebuild, cam, headers, and blower all installed at the same time. New opti and 42# injectors too. I'm not sure it doesn't have some mechanical or ignition issues also. I've tuned lots of FI LS1s and none have given me the problems this car has.

 

I don't know what is wrong, but I doubt it has anything to do with the MAF.

Rich

 

I know this pretty much gets beat to death anytime someone has an rpm related problem. But, are you sure the opti is in good condition? I didn't see anything in your post that said this car was or wasn't running one so I thought I'd throw that in as a possibility. How about the rest of the ignition system? Any reason to suspect a coil or ign. module problem?

Got a couple more questions:
1. What injectors are being used? (stock or other)
2. Has the ignition been upgraded? (MSD box or other)
3. What spark plugs are in it and what's the gap?

 

Call Jeff Creech at carolina auto masters. He can tell what the problem is and it is the MAF

 

1. http://www.racetronix.com/621031.html
2. New GM Opti, new wires, no box of any kind
3. NGK TR6, .034

leebaker1973, it would be hard for me to call a professional tuner who charges for his services and ask for free advise. I figure that's what these forums are for.

 

Please don't call jeff creech for anything

 

It sounds ignition related to me. Have you checked your knock retard it could be pulling a whole bunch of timing. Also check cat overtemp protection. It could be adding a ton of fuel causing it to bog down at high rpm. Have you checked it with a wideband. If you don't have a wideband it should be approximately .93mv on your stock O2's.

 

My stock MAF would max out at 5K rpm when I was running 10 psi. I was making about 480RWHP by 6K rpm though. I would guess it would max out around 425RWHP????

 

I'm guessing from the injector size you're not using an FMU. So that eliminates one thought that it could have been stock injectors locking up at high rail pressure. I'm wondering about the ignition side. New Opti is a good start. I run Autolites so I'm not familiar with the NGK plug # to use but I suspect it's the equivalent. I do know from experience with my car that without an aftermarket ignition box I would blow out the spark under boost by approximately 5000 RPM even with the plugs gapped down to .035".
Even though the 96-97 years are supposed to have a hotter coil I didn't find it to be enough without a little help.

FWIW. I still needed to keep the gap under .035". I had the best results with .030". But from what I've been told the Accel 300+ might not have been the best box to use.

You did say that it still hits a wall and falls on it's face even with the high MAF diagnostic disabled right? Or did I read that wrong?

 

Sounds like an ignition problem to me. Not enough spark or it's getting blown out by the blower.