I have a 2007 TrailBlazer SS, and I modified the airbox to seal to the ramair hood that I bought. Now the truck it throwing lean codes, and is shifting hard like the MAF is confused. I am not sure which settings that I to change, I think it is the MAF frequency table.. but I am not 100% sure. Any help is appreciated.
Yes Start by correcting the MAF. Log STFTs and get it dialed in within 0-2% and should help out.
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Do you have any other modifications? Have you already tuned the vehicle? From the factory they run on the rich side and I'd be really surprised if that change alone got you to throw a lean code. You might have bumped something under the hood. Take a quick log with some normal and mid rpm driving, carefully check your PE target at low RPMs (<3500) with a WB if you have one.
I agree with Shane that you need to correct MAF table, but like I said I'm surprised it was a large enough delta to trigger a lean condition and cause shifting issues.
Bone stock motor. 4" intake, LS7 MAF, ramair hood with airbox sealed to the opening in the hood. I did an e-mail tune from a company in North Carolina. Sent logs, and they modified the tune a couple of times. Was running great before I sealed the airbox to the hood opening.
Attached logs from last night.
So, I watched the logs, and when the AFR went below 14, I looked at the MAF hz, and upped the engine > airflow > Airflow vs freq low and Airflow vs freq high from that hz up.... reflashed, and did it again. Not shifting hard anymore, but still throwing lean codes.
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Woah, I took a look at your log and holy fucking KR. Do you have a wideband? What's your AFR while the car is pulling the 11.3 degrees of timing?!
I don't have widebands. The AFR from the factory O2s is 14.6 until the MAF reads about 5.9Khz, then it drops to 12.3, so when the KR is sky hi, the AFR reading is at 14.6.
I didn't modify anything other than using some HVAC sealing foam to fill any gaps around the airbox that would be pulling air from anywhere other than the ramair hood. As soon as that was done, the truck was angry.
I decided to compare logs from before and after I sealed the airbox... results are interesting..
ENGINE SPEED, TRUCK SPEED, THROTTLE %, MAF AIRFLOW PER MIN, MAF FREQ
before airbox seal:
5429rpm, 70mph, 83%, 48.985lbs, 8602hz
5722rpm, 74mph, 83%, 47.928lbs, 8639hz
2135rpm, 63mph, 36%, 5.773lbs, 4246hz
max flow 50ish lbs
After airbox seal:
5427rpm, 70mph, 83%, 31.798lbs, 7782hz
5721rpm, 74mph, 83%, 33.296lbs, 7858hz
2167rpm, 64mph, 36%, 3.530lbs, 3472hz
max flow 35ish lbs
From what I can tell, I am getting less air now...
I could see that outcome being logical, unless the ram air makes up for the box being sealed (which it isn't according to your numbers) the engine is now breathing through a longer/smaller straw.
Did you have KR before the airbox seal? Remove the seal and do a log, I'd be really concerned about that KR.
It seems you may have increased the air quality at a critical expense of air quantity.
Last edited by VodeAn; 01-05-2014 at 12:13 PM.
Nope, no KR before, or at least not much. I removed the foam from the front of the airbox, so it is now just the K&N heat shield in front of the filter. I will see how the truck reacts tomorrow.
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