crainholio

iTrader: (2)

Engine is a 2001 LS1 with a TR224 (0.563" int/exh, 224deg @ 0.50 int/exh) installed in an '82 Camaro Z28. No other engine mods.

Induction tract is factory '88 IROC, Y-shaped plastic snorkel with an ~6"x6" filter panel at each end of the Y, using a 3.5" diameter silicon hose to connect the snorkel to the '01 MAF.

Running the car in SD mode w/ MAF fail set to 1Hz and MAF physically disconnected, high-octane spark map copied over the low-octane spark map, my LTFTs are in the -2.3% to +1.8% range...VE table is stock.

With my MAF connected and enabled, my LTFTs max out at 25% immediately. Car does not want to idle until CL enables.

I've been incrementally scaling the MAF table and re-testing. Finally got LTFTs into the -3.x to +2.3 range under normal cruise...MAF table is now scaled to 134% of stock.

Two questions to present, and I appreciate any feedback:
1.) 34% MAF error seems like a big jump. Acceptable, or indicative of a problem such as vacuum leak?

2.) Deceleration LTFT cells show me in the +11% to +19% range. My EFILive v.7 scanner shows the LTFTs immediately jumping to +11% and up when I partially lift the throttle and decelerate. Running in SD mode I saw no such jump. Is this indicative of a problem?

I appreciate any input or suggested diagnostic steps. I have EFILive v.7 and LS1Edit 1.52s.

Patrick G

iTrader: (14)

I don't think it's possible to have near perfect fuel trims with a TR224 cam and stock VE tables if the MAF is disabled and unplugged. What happens when you turn off the L-Trims and work only off of S-Trims? Is the MAF in good shape? Not dirty? Is the screen knocked out? Might help if you posted up the tune.

crainholio

iTrader: (2)

Thanks Patrick. I'll hit each of your points below:

1) I tested 2 MAFs, a GM replacement 78mm stock piece w/ honeycomb air straightener, and the '01 factory MAF with no honeycomb. Both show similar behavior...LTFT shoots to +11% and upward soon as the MAF is enabled. I cleaned both with CRC MAF Cleaner aerosol, no effect.

2) Will disable LTFT tonight and re-test to see how STFTs respond.

3) I use LS1Edit, glad to post the .LS1 tune file and hope it's legible to your software.

turbolx

Completely possible, and very likely in my experience. You took the MAF out of its native environment of the stock LS1 airbox (remember those?) with a "squished" narrow oval inlet to the MAF element and put it behind a relatively huge 3.5" tube. This is going to change the way you distribute the air molecules across the entire area of the MAF. Sure, it's better for flow. But it IS different. As long as you properly account for this change in the calibration, everything should fall into place. I wouldn't lose any sleep over it.

crainholio

iTrader: (2)

Greg, I'm a big fan of your two tuning books and appreciate your reply.

My initial theory was that the altered induction tract was causing the MAF to under-report the air volume.

However, I couldn't account for a 34% deviation just by adding 2" length of 3.5" tubing between the MAF and the Y-snorkel...which has both legs of the "Y" as well as the forward portion of the trunk squished into a rectangular duct. Only the aft end of the "Y" opens up to a 3.5" round aperture.

I haven't even seen a K&N cold air intake kit cause more than a ~10% change in my limited experience, so this 34% error gave me some concern.

crainholio

iTrader: (2)

Further thinking...

All the various stock MAF calibration tables I have in my bin library, as well as JimmyBlue's compiled Excel sheet had no values even approaching what I now have at 134%. Trucks, Monaro, Vettes, etc...the values were significantly lower than mine.

New working theory is that excessive air velocity from the relatively small IROC induction tract forward of the MAF may be the root cause of the MAF under-reporting. The legs of the "Y" are nearly 10" in length, and very narrow rectangular shape in order to fit over the radiator and under the hood...similar to the newer Corvette duct but only ~3/4" high.

A very long, narrow path for air to flow...my limited knowledge of Physics leads me to believe that would yield a higher velocity than a larger and/or shorter duct. Correct?

Assuming the above is correct, the higher velocity may explain the MAF under-reporting airflow. Need to gather up some ducting pieces and install a more typical large intact tract to test this theory...

BLK02WS6

iTrader: (2)

Personally, if the injector tables are correct for the installed injectors, I would put it in open loop, put a wideband in it and tune the VE tables in speed density... then tune the MAF table with the wideband and go with it... if it's 34%, so be it...